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709 Commits

Author SHA1 Message Date
Eric Kim
f52b3b89fa mm/rmap: synchronize lock and unlock target in anon_vma_clone 
Currently, in anon_vma_clone(), src vma's anon_vma is assigned to
active_anon_vma and is used when unlocking anon_vma after linking new
AVCs.  However, the anon_vma is locked using src->anon_vma, instead of
active_anon_vma, making the lock and unlock target inconsistent.

Use active_anon_vma for both locking and unlocking.

Link: https://lore.kernel.org/OS7PR01MB139142FE16EC63B892559D40496DA2@OS7PR01MB13914.jpnprd01.prod.outlook.com
Signed-off-by: Eric Kim <seohyun.kim@outlook.kr>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-24 18:43:25 -07:00
Baolin Wang
3bf07ce805 mm: vmscan: convert folio_referenced() to use vma_flags_t 
Patch series "promote mapped executable folios after first usage for
MGLRU", v4.

Now MGLRU's protection of mapped executable file folios is less reliable. 
Follow the classical LRU's logic, promoting mapped executable file folios
after their first usage to give executable code a better chance to stay in
memory and improve workload performance (See patch 2 for more details).


This patch (of 3):

Replace use of the legacy vm_flags_t flags with vma_flags_t values for
folio_referenced() and related logic.  This is also a preparation for the
following changes.

No functional changes.

Link: https://lore.kernel.org/cover.1784509721.git.baolin.wang@linux.alibaba.com
Link: https://lore.kernel.org/2bd39e16ec19e3e3c4716aa9a1a25775c26cac57.1784509721.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-24 18:42:54 -07:00
Lorenzo Stoakes (ARM)
93c0c8dc87 mm/rmap: use anon pgoff to track MAP_PRIVATE file-backed anon folios 
Currently anonymous folios belonging to CoW'd MAP_PRIVATE file-backed
mappings are indexed by their page offset within the file in which they
were originally mapped.

This differs from anonymous folios belonging to pure anon mappings which
are indexed by their anonymous page offset (the address at which they'd
belong in the VMA when first faulted).

This change fixes this inconsistency, always indexing anonymous folios by
their anonymous page offset regardless of the VMA to which they belong.

The foundations have been laid such that we need only switch this
functionality on such by:

* Using linear_anon_page_index() in __folio_set_anon() to assign the
  folio's index to the anonymous linear index rather than the file-backed
  one.

* Otherwise using linear_anon_page_index() in all instances where
  anonymous folios are being referenced or manipulated.

* Replacing vma_address() with vma_filebacked_address() or
  vma_anon_address() as appropriate.

* Updating the merging logic to check that anonymous page offsets are
  aligned as well as filebacked ones for MAP_PRIVATE file-backed VMAs,
  introducing needs_adjacent_anon_pgoff() to figure out when this is
  required.

* Updating linear_folio_page_index() to invoke linear_anon_page_index()
  if the folio is anonymous.

* Updating vma_address_end() to use the VMA's anonymous page offset when
  pvmw->pgoff is anonymous.

* Correcting folio_within_range() to use anonymous page offset for
  anonymous folios.

This will have no impact on merging of anonymous VMAs, whose page offset
and anonymous page offset are identical, nor will it impact shared
file-backed VMAs, which will continue to be merged based on the
file-backed page offset.

However, MAP_PRIVATE file-backed mappings must now be aligned on anonymous
page offset as well.

In most instances this should have no impact on merging of file-backed
mappings, which are usually not merged all that often, let alone
MAP_PRIVATE mapped ones, and rarely remapped and faulted before being
moved back in place (the case in which a merge may now fail).

One subtle impact of this change is in NUMA interleaving - since commit
88c91dc585 ("mempolicy: migration attempt to match interleave nodes"),
migration heuristically tries to maintain interleaving behaviour matching
the policy using folio indices.

When doing migration of CoW'd MAP_PRIVATE-file backed ranges, the 'base'
upon which the interleaving behaviour is performed will vary for these
ranges.  However the commit notes that ranges spanning multiple VMAs will
already cause varying bases, and that this is an acceptable approximation.

It is very unlikely real world use-cases will be impacted by this
(MAP_PRIVATE file-backed mappings are already an edge case), and all that
will happen is that such ranges will cause interleaving to be rotated over
the CoW'd range, with little to no impact.

This commit lays the foundations for future scalable CoW work which needs
to track some remaps, meaning that most remap tracking can be avoided, and
in nearly all cases the anonymous page offset will be able to be used to
quickly find the VMA in an mm.

Note that the need_rmap_locks check doesn't need to be updated, as any
remapping will offset both the anonymous and file-backed page offset, so
it suffices to check only one.

Link: https://lore.kernel.org/20260813-b4-scalable-cow-virt-pgoff-v5-14-c21581c0c3c8@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Deucher <alexander.deucher@amd.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christan König <christian.koenig@amd.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Gregory Price (Meta) <gourry@gourry.net>
Cc: Harry Yoo <harry@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ray <Ray.Huang@amd.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Namhyung kim <namhyung@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-24 18:42:53 -07:00
Lorenzo Stoakes (ARM)
50c5f35a64 mm/rmap: track whether the page VMA mapped pgoff is anonymous 
Update the page_vma_mapped_walk structure to track whether the pgoff being
tracked is an anonymous pgoff or not and update the comments to reflect
this.

This is necessary in order to determine the correct VMA page offset in
vma_address_end() when pvmw->nr_pages > 1.

Also document that pvmw->pgoff is meaningless for pvmw->nr_pages == 1 and
for KSM.

Do not set this field where pgoff is not specified.

This is laying the groundwork for eventually using anonymous page offsets
as the index for all anonymous folios.

No functional change intended.

Link: https://lore.kernel.org/20260813-b4-scalable-cow-virt-pgoff-v5-10-c21581c0c3c8@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Deucher <alexander.deucher@amd.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christan König <christian.koenig@amd.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Gregory Price (Meta) <gourry@gourry.net>
Cc: Harry Yoo <harry@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ray <Ray.Huang@amd.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Namhyung kim <namhyung@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-24 18:42:52 -07:00
Lorenzo Stoakes (ARM)
dba10745e9 mm: introduce and use vma_filebacked_address() 
In cases where we know that the VMA is file-backed, use
vma_filebacked_address() rather than vma_address().

This lays the foundation for using the anonymous page offset via
vma_anon_address().

Also add an assert to ensure that the VMA whose address is required is not
anonymous.

No functional change intended.

Link: https://lore.kernel.org/20260813-b4-scalable-cow-virt-pgoff-v5-6-c21581c0c3c8@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Tested-by: syzbot@syzkaller.appspotmail.com
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Deucher <alexander.deucher@amd.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christan König <christian.koenig@amd.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Gregory Price (Meta) <gourry@gourry.net>
Cc: Harry Yoo <harry@kernel.org>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Huang Ray <Ray.Huang@amd.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Namhyung kim <namhyung@kernel.org>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-24 18:42:51 -07:00
Dev Jain
4fe4ea4cbe mm/rmap: batch unmap file folios belonging to uffd-wp VMAs 
Commit a67fe41e21 ("mm: rmap: support batched unmapping for file large
folios") extended batched unmapping for file folios.  That also required
making pte_install_uffd_wp_if_needed() support batching, but that was left
out for the time being.  Correctness was maintained by stopping batching
if the VMA the folio belongs to is marked uffd-wp.

Now that cond_install_uffd_wp_ptes() supports batching, call it with the
full batch length and allow folio_unmap_pte_batch() to batch file folios
belonging to uffd-wp VMAs.

For file folios, if the uffd-wp bit is set, unmapping converts present
PTEs into uffd-wp markers.  We must ensure that the same PTE range is not
reprocessed by the try_to_unmap_one() loop.

The page_vma_mapped_walk API ensures this: check_pte() only returns true
if any PFN in [pvmw->pfn, pvmw->pfn + nr_pages) is mapped by the PTE. 
There is no PFN underlying a uffd-wp marker PTE, so check_pte() returns
false and the walk skips ahead until it reaches a present entry again.

Link: https://lore.kernel.org/20260720065508.2695106-4-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-06 18:57:21 -07:00
Dev Jain
4259767463 mm/memory: batch set uffd-wp markers during zapping 
Enable batch setting of uffd-wp PTE markers.

The code paths passing nr > 1 to zap_install_uffd_wp_if_needed() produce
that nr through either folio_pte_batch() or swap_pte_batch(), therefore
batching is correct:

1) All PTEs belong to the same type of VMA: anonymous or non-anonymous,
   wp-armed or non-wp-armed.

2) All PTEs are either marked with uffd-wp or not marked with uffd-wp;
   the same applies to the pte_swp_uffd_any() check.

3) uffd_supports_wp_marker() is independent of the function parameters.

Use set_pte_at() in a loop instead of set_ptes(), because set_ptes()
cannot handle nonpresent to nonpresent conversion for nr_pages > 1.

Rename the helper to cond_install_uffd_wp_ptes().

Link: https://lore.kernel.org/20260720065508.2695106-3-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-06 18:57:20 -07:00
Dev Jain
04b09ca57d mm/rmap: add anon folio unmap dispatcher 
Add ttu_anon_folio() as the common entry point for anonymous folio
unmapping.  It dispatches to the lazyfree or swapbacked helper as
appropriate.

Keep restoration of cleared PTEs in the caller, where the PTEs were
removed.

No functional change intended.

Link: https://lore.kernel.org/20260730094559.418003-6-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:19:07 -07:00
Dev Jain
0caf74274d mm/rmap: refactor anon folio unmap in try_to_unmap_one 
Refactor anonymous swapbacked folio unmap to ttu_anon_swapbacked_folio(). 
While at it, rename the remaining subpage variables to page; folios have
pages, not subpages.

No functional change intended.

Link: https://lore.kernel.org/20260730094559.418003-5-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:19:06 -07:00
Dev Jain
0955037b98 mm/rmap: refactor some code around lazyfree folio unmapping 
For lazyfree folio unmapping, after clearing the ptes we must abort the
operation if the folio got dirtied or it has unexpected references.

Refactor this logic into a function which will return whether we need
to abort or not.

If we abort, we restore the ptes and bail out of try_to_unmap_one.
Otherwise adjust the rss stats of the mm and jump to a label.

Also rename that label from "discard" to "finish_unmap"; the former
is appropriate in the lazyfree context, but the code following the label
is executed for other successful unmap code paths too, so 'discard' does
not sound correct for them.

No functional change intended.

Link: https://lore.kernel.org/20260730094559.418003-4-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:19:06 -07:00
Dev Jain
d4ec557282 mm/rmap: add try_to_unmap_poisoned_hugetlb_one 
Simplify try_to_unmap_one() by separating the hugetlb parts into
try_to_unmap_poisoned_hugetlb_one().

To understand the correctness of the refactoring, the following points
are noted:

1. try_to_unmap() is called for hugetlb folios only when they are
   hwpoisoned.

2. A hugetlb VMA cannot be mlocked.

3. page_vma_mapped_walk() returns at most one hugetlb mapping in a VMA,
   and that mapping points at the head PFN.

4. We won't ever process a softleaf entry that encodes a hugetlb folio;
   hugetlb folios are never swapped out, migration entries will be
   skipped (PVMW_MIGRATION not passed), and device-exclusive does not
   work for hugetlb.

5. The hwpoison entry is constructed from the poisoned folio, just as in
   the pre-refactor code. Any previous uffd-wp state is deliberately not
   preserved for the hwpoison entry.

6. TTU_HWPOISON is always present; for it to not be present, either the
   folio has to be in swapcache, or mapping_can_writeback() is true (see
   unmap_poisoned_folio), none of which is true for hugetlb folios.

7. Hugetlb uses separate counters from normal rss counters, therefore
   update_highwater_rss() need not be called.

While at it:

 - Change VM_BUG_* to VM_WARN_*.

 - Do not declare variables which are only used once.

 - Constify some variables.

 - Add some more VM_WARN_* to assert some invariants.

Except the above 4 points, no functional change intended.

Link: https://lore.kernel.org/20260730094559.418003-3-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:19:06 -07:00
Dev Jain
af56d6acf4 mm/rmap: convert page -> folio for hwpoison checks 
Patch series "mm/rmap: Refactor try_to_unmap_one", v4.

In preparation for batching anonymous large folio unmapping to optimize
it, refactor try_to_unmap_one.  This series refactors hugetlb,
anon-lazyfree and anon-swapbacked logic into their own functions,
significantly reducing the length of the huge try_to_unmap_one.


This patch (of 5):

try_to_unmap() receives hugetlb folios only from the hwpoison path. 
hugetlb_update_hwpoison() sets the hugetlb folio's head-page hwpoison bit,
and page_vma_mapped_walk() reports the hugetlb mapping at the head PFN, so
the previous PageHWPoison(subpage) check happened to work for hugetlb.

For non-hugetlb folios, unmap_poisoned_folio() currently rejects large
folios before calling try_to_unmap().  Hence it is always the case that if
try_to_unmap_one() handles an hwpoisoned folio, then the head page is
marked with the poison bit.

Therefore, convert the poisoned subpage checks to folio_test_hwpoison().

No functional change intended, except that, while at it,
convert VM_BUG_* to VM_WARN_*.

Link: https://lore.kernel.org/20260730094559.418003-1-dev.jain@arm.com
Link: https://lore.kernel.org/20260730094559.418003-2-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:19:06 -07:00
Lorenzo Stoakes
b1e71c05fa mm/rmap: rename anon_vma_interval_tree_*() to anon_rmap_tree_*() 
To be consistent with the newly renamed mapping_rmap_tree_*(), rename the
anon_vma_interval_tree_*() helpers to anon_rmap_tree_*().

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-11-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:58 -07:00
Lorenzo Stoakes
68364437ec mm/rmap: parameterise anon_vma_interval_tree_*() by anon_vma 
Similar to what we did with mapping_rmap_tree*(), let's declare
anon_vma_interval_tree*() in terms of anon_vma rather than rb_root_cached.

In each case the rb tree referenced is &anon_vma->rb_root, so just pass
anon_vma and the functions can figure this out themselves.

Also update the VMA userland tests to reflect the change.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-9-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:58 -07:00
Lorenzo Stoakes
4b7a90a48b mm/rmap: rename vma_interval_tree_*() to mapping_rmap_tree_*() 
The family of vma_interval_tree_() functions manipulate the
address_space (which, of course, is generally referred to as 'mapping')
reverse mapping, but are named the 'VMA' interval tree.

VMAs may be mapped by an anon_vma, an address_space, or both. Therefore
calling the mapping interval tree a 'VMA' interval tree is rather
confusing.

This is also inconsistent with the anon_vma_interval_tree_*() functions
which explicitly reference the rmap object to which they pertain.

Rename the vma_interval_tree_*() functions to mapping_rmap_tree_*() to
correct this.

We will rename the anon rmap functions similarly in a subsequent patch.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-8-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:58 -07:00
Lorenzo Stoakes
7a67b96af0 mm/rmap: parameterise vma_interval_tree_*() by address_space 
The file-backed mapping interval tree functions vma_interval_tree_*()
accept a raw rb_root_cached pointer to determine the tree in which they are
operating.

However, in each case, this is always associated with an address_space data
type.

So simply pass a pointer to that instead to simplify the code, and more
clearly differentiate between these operations and those concerning
anonymous mappings.

While we're here, make the generated interval tree functions static as they
do not need to be used externally (any previously existing external users
have now been removed).

We also rename VMA parameters from 'node' to 'vma' as calling this a node
is simply confusing, update the input index types to pgoff_t since they
reference page offsets and rename the parameters to pgoff_start and
pgoff_last.

No functional change intended.

Link: https://lore.kernel.org/20260710-b4-pre-scalable-cow-v2-6-2a5aa403d977@kernel.org
Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Gregory Price <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Kai Huang <kai.huang@intel.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: SJ Park <sj@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:57 -07:00
Kiryl Shutsemau (Meta)
7974c23853 mm: handle VM_UFFD_RWP in khugepaged, rmap, and GUP 
Three mm paths outside the fault handler gate on the uffd PTE bit today:
khugepaged (skip collapse on ranges carrying markers), rmap (cap unmap
batching), and GUP (force a fault through gup_can_follow_protnone). 
Extend each to treat VM_UFFD_RWP the same as VM_UFFD_WP; otherwise per-PTE
RWP state is silently destroyed or bypassed.

khugepaged: try_collapse_pte_mapped_thp() and
file_backed_vma_is_retractable() already refuse to collapse or retract
page tables on ranges carrying the uffd PTE bit.  Broaden the VMA
predicate from userfaultfd_wp() to userfaultfd_protected() so VM_UFFD_RWP
ranges get the same protection.  hpage_collapse_scan_pmd() needs no change
— its existing pte_uffd() check already catches an RWP PTE because it
carries the uffd bit.

rmap: folio_unmap_pte_batch() caps batching at 1 for VM_UFFD_RWP so the
restore path handles each PTE with its own marker.

GUP: gup_can_follow_protnone() forces a fault on VM_UFFD_RWP VMAs
regardless of FOLL_HONOR_NUMA_FAULT.  RWP uses protnone as an
access-tracking marker, not for NUMA hinting, so any GUP — read or write
— must go through the userfaultfd fault path.

Link: https://lore.kernel.org/20260708111417.173443-9-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam@infradead.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:38 -07:00
Kiryl Shutsemau (Meta)
c0ffe79eed mm: rename uffd-wp PTE accessors to uffd 
Userfaultfd RWP will reuse the uffd-wp PTE bit to mark access-tracking
PTEs, alongside the write-protected ones it already marks.  The bit's
meaning now depends on the VMA flag (WP or RWP), not on its name.

Rename the kernel-internal names that describe the bit:

  - pte/pmd/huge_pte accessors (and swap variants)
  - pgtable_supports_uffd() capability query
  - SCAN_PTE_UFFD khugepaged enum

The ftrace string emitted by mm_khugepaged_scan_pmd for this enum is
kept as "pte_uffd_wp" so existing trace-based tooling keeps matching.

Pure mechanical rename -- no behavior change.

Link: https://lore.kernel.org/20260708111417.173443-4-kirill@shutemov.name
Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
Assisted-by: Claude:claude-opus-4-6
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: James Houghton <jthoughton@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-08-04 19:18:36 -07:00
Dev Jain
9be12ffa78 mm/rmap: use huge_ptep_get() in try_to_migrate_one() 
try_to_migrate_one() is used by folio migration to replace a present
mapping with a migration entry. For hugetlb folios, page_vma_mapped_walk()
returns the pte pointer to the hugetlb folio in pvmw.pte, but the code
reads the huge pte entry with ptep_get().

On arches which provide their own huge_ptep_get() to dereference a huge
pte pointer, accessing via ptep_get() would cause pte_pfn(), pte_present()
etc to misbehave.

It is not clear whether this has a trivially visible effect to userspace.

Use huge_ptep_get() to dereference a huge pte pointer.

Commit a98a2f0c8c copied the bug from try_to_unmap_one into
try_to_migrate_one.

[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lore.kernel.org/20260703114202.365553-4-dev.jain@arm.com
Fixes: a98a2f0c8c ("mm/rmap: split migration into its own function")
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Harry Yoo <harry@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Jann Horn <jannh@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Jun'ichi "Nick" Nomura <j-nomura@ce.jp.nec.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-30 19:40:45 -07:00
Dev Jain
f5407e9b69 mm/rmap: use huge_ptep_get() in try_to_unmap_one() 
Patch series "Fix incorrect access of hugetlb pte entries", v3.

There are various places which use ptep_get() to get the pte entry
corresponding to a hugetlb folio.  Some arches (like s390) have special
handling to compute the pteval, so they provide huge_ptep_get().  Use this
helper consistently.

Additionally, some code paths may provide huge_ptep_get with an unaligned
address.  This is a problem on arm64 (I checked other arches and it looks
fine for them), which is fixed in patch 1.  The fix is made to be
backport-friendly: the cleaner fix would be to perhaps pass the hstate to
huge_ptep_get() - that is wider churn and we can do that later.


This patch (of 5):

try_to_unmap_one() handles hugetlb folios when memory failure needs to
replace a poisoned hugetlb mapping with a hwpoison entry.  In that case
page_vma_mapped_walk() returns the pte pointer to the hugetlb folio in
pvmw.pte, but the code reads it with ptep_get().

On arches which provide their own huge_ptep_get() to dereference a huge
pte pointer, accessing via ptep_get() would cause pte_pfn(), pte_present()
etc to misbehave.

It is not clear whether this has a trivially visible effect to userspace.

Just use huge_ptep_get() for dereferencing a huge pte pointer.

Link: https://lore.kernel.org/20260703114202.365553-1-dev.jain@arm.com
Link: https://lore.kernel.org/20260703114202.365553-3-dev.jain@arm.com
Fixes: c7ab0d2fdc ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()")
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reported-by: David Hildenbrand <david@kernel.org>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Harry Yoo <harry@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Jann Horn <jannh@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Jun'ichi "Nick" Nomura <j-nomura@ce.jp.nec.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-30 19:40:45 -07:00
Usama Arif
d547b10017 mm: rename ARCH_ENABLE_THP_MIGRATION to ARCH_HAS_PMD_SOFTLEAVES 
CONFIG_ARCH_ENABLE_THP_MIGRATION gates PMD-level migration entries. 
PMD-level device-private entries use the same migration mechanism and
therefore require the same architecture support.

Upcoming PMD-level swap entries can use the same PMD softleaf helpers
without depending on page migration, so rename the architecture gate to
CONFIG_ARCH_HAS_PMD_SOFTLEAVES.  This describes the PMD entry capability
rather than one current user of it.

This is a pure rename: the set of selecting architectures (x86, arm64,
s390, riscv, loongarch, and powerpc on PPC_BOOK3S_64) and the gating
semantics are unchanged.

No functional change intended.

Link: https://lore.kernel.org/20260706114320.1643046-7-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-30 19:40:25 -07:00
Usama Arif
b707057443 mm: extract mm_prepare_for_swap_entries() helper 
When a swap entry is installed in a page table, the mm must be added to
init_mm.mmlist so that swapoff can find and unuse its swap entries.  This
double-checked locking pattern is currently open-coded in
try_to_unmap_one() and copy_nonpresent_pte().

Move it into mm_prepare_for_swap_entries() in mm/internal.h and convert
both callers so it can be reused by upcoming PMD-level swap entry code
paths that also need to register the mm with swapoff.

copy_nonpresent_pte() previously inserted into &src_mm->mmlist rather than
&init_mm.mmlist, but the insertion point is irrelevant, mmlist is a
circular list and swapoff walks it entirely from init_mm.mmlist, so only
membership matters, not position.

Link: https://lore.kernel.org/20260706114320.1643046-3-usama.arif@linux.dev
Signed-off-by: Usama Arif <usama.arif@linux.dev>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alexandre Ghiti <alex@ghiti.fr>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Kiryl Shutsemau <kas@kernel.org>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-07-30 19:40:23 -07:00
David Hildenbrand (Arm)
90f01f5d6b mm: remove page_mapped() 
Let's replace the last user of page_mapped() by folio_mapped() so we can
get rid of page_mapped().

Replace the remaining occurrences of page_mapped() in rmap documentation
by folio_mapped().

Link: https://lore.kernel.org/20260427-page_mapped-v1-3-e89c3592c74c@kernel.org
Signed-off-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrii Nakryiko <andrii@kernel.org>
Cc: Eduard Zingerman <eddyz87@gmail.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rich Felker <dalias@libc.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Song Liu <song@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Yonghong Song <yonghong.song@linux.dev>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-28 21:04:57 -07:00
Dev Jain
3f8968e9cb mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one 
Initialize nr_pages to 1 at the start of each loop iteration, like
folio_referenced_one() does.

Without this, nr_pages computed by a previous folio_unmap_pte_batch() call
can be reused on a later iteration that does not run
folio_unmap_pte_batch() again.

mmap a 64K large folio with MAP_ANONYMOUS | MAP_DROPPABLE, then call
madvise(MADV_FREE), then make the last page device-exclusive via
HMM_DMIRROR_EXCLUSIVE.

Trigger node reclaim through sysfs.  Now, in try_to_unmap_one(), we will
first clear the first 15 out of 16 entries mapping the lazyfree folio. 
This will set nr_pages to 15.  In the next pvmw walk, this nr_pages gets
reused on a device-exclusive pte, thus potentially corrupting folio
refcount/mapcount.

At the moment, I have a userspace program which can make the kernel spit
out a trace, but the blow up is in folio_referenced_one(), because there
are existing bugs in the interaction between device-private and rmap
(which too I am investigating).  I did a one liner kernel change to avoid
going into folio_referenced_one(), and the kernel blows up at
folio_remove_rmap_ptes in try_to_unmap_one which is what I wanted.

Note that the bug is there not since file folio batching but lazyfree
folio batching, since device-exclusive only works for anonymous folios.

Userspace visible effect is simply kernel crashing somewhere due to
refcount/mapcount corruption.

Link: https://lore.kernel.org/20260518063656.3721056-1-dev.jain@arm.com
Fixes: 354dffd295 ("mm: support batched unmap for lazyfree large folios during reclamation")
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: Barry Song <baohua@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-05-21 19:06:12 -07:00
Leno Hou
a6a8c087dc mm/mglru: fix cgroup OOM during MGLRU state switching 
When the Multi-Gen LRU (MGLRU) state is toggled dynamically, a race
condition exists between the state switching and the memory reclaim path. 
This can lead to unexpected cgroup OOM kills, even when plenty of
reclaimable memory is available.

Problem Description
==================
The issue arises from a "reclaim vacuum" during the transition.

1. When disabling MGLRU, lru_gen_change_state() sets lrugen->enabled to
   false before the pages are drained from MGLRU lists back to traditional
   LRU lists.
2. Concurrent reclaimers in shrink_lruvec() see lrugen->enabled as false
   and skip the MGLRU path.
3. However, these pages might not have reached the traditional LRU lists
   yet, or the changes are not yet visible to all CPUs due to a lack
   of synchronization.
4. get_scan_count() subsequently finds traditional LRU lists empty,
   concludes there is no reclaimable memory, and triggers an OOM kill.

A similar race can occur during enablement, where the reclaimer sees the
new state but the MGLRU lists haven't been populated via fill_evictable()
yet.

Solution
========
Introduce a 'switching' state (`lru_switch`) to bridge the transition.
When transitioning, the system enters this intermediate state where
the reclaimer is forced to attempt both MGLRU and traditional reclaim
paths sequentially. This ensures that folios remain visible to at least
one reclaim mechanism until the transition is fully materialized across
all CPUs.

Race & Mitigation
================
A race window exists between checking the 'draining' state and performing
the actual list operations. For instance, a reclaimer might observe the
draining state as false just before it changes, leading to a suboptimal
reclaim path decision.

However, this impact is effectively mitigated by the kernel's reclaim
retry mechanism (e.g., in do_try_to_free_pages). If a reclaimer pass fails
to find eligible folios due to a state transition race, subsequent retries
in the loop will observe the updated state and correctly direct the scan
to the appropriate LRU lists. This ensures the transient inconsistency
does not escalate into a terminal OOM kill.

This effectively reduce the race window that previously triggered OOMs
under high memory pressure.

This fix has been verified on v7.0.0-rc1; dynamic toggling of MGLRU
functions correctly without triggering unexpected OOM kills.

Link: https://lkml.kernel.org/r/20260319-b4-switch-mglru-v2-v5-1-8898491e5f17@gmail.com
Signed-off-by: Leno Hou <lenohou@gmail.com>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Axel Rasmussen <axelrasmussen@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Jialing Wang <wjl.linux@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Bingfang Guo <bfguo@icloud.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:33 -07:00
Baolin Wang
56e5b60b21 mm: support batched checking of the young flag for MGLRU 
Use the batched helper test_and_clear_young_ptes_notify() to check and
clear the young flag to improve the performance during large folio
reclamation when MGLRU is enabled.

Meanwhile, we can also support batched checking the young and dirty flag
when MGLRU walks the mm's pagetable to update the folios' generation
counter.  Since MGLRU also checks the PTE dirty bit, use
folio_pte_batch_flags() with FPB_MERGE_YOUNG_DIRTY set to detect batches
of PTEs for a large folio.

Then we can remove the ptep_test_and_clear_young_notify() since it has no
users now.

Note that we also update the 'young' counter and 'mm_stats[MM_LEAF_YOUNG]'
counter with the batched count in the lru_gen_look_around() and
walk_pte_range().  However, the batched operations may inflate these two
counters, because in a large folio not all PTEs may have been accessed. 
(Additionally, tracking how many PTEs have been accessed within a large
folio is not very meaningful, since the mm core actually tracks
access/dirty on a per-folio basis, not per page).  The impact analysis is
as follows:

1. The 'mm_stats[MM_LEAF_YOUNG]' counter has no functional impact and
   is mainly for debugging.

2. The 'young' counter is used to decide whether to place the current
   PMD entry into the bloom filters by suitable_to_scan() (so that next
   time we can check whether it has been accessed again), which may set
   the hash bit in the bloom filters for a PMD entry that hasn't seen much
   access.  However, bloom filters inherently allow some error, so this
   effect appears negligible.

Link: https://lkml.kernel.org/r/378f4acf7d07410aa7c2e4b49d56bb165918eb34.1772778858.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:16 -07:00
Baolin Wang
83ec1286b1 mm: rmap: add a ZONE_DEVICE folio warning in folio_referenced() 
The folio_referenced() is used to test whether a folio was referenced
during reclaim.  Moreover, ZONE_DEVICE folios are controlled by their
device driver, have a lifetime tied to that driver, and are never placed
on the LRU list.  That means we should never try to reclaim ZONE_DEVICE
folios, so add a warning to catch this unexpected behavior in
folio_referenced() to avoid confusion, as discussed in the previous
thread[1].

[1] https://lore.kernel.org/all/16fb7985-ec0f-4b56-91e7-404c5114f899@kernel.org/
Link: https://lkml.kernel.org/r/64d6fb2a33f7101e1d4aca2c9052e0758b76d492.1772778858.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:15 -07:00
Vernon Yang
6cc153f90b mm: add folio_test_lazyfree helper 
Add folio_test_lazyfree() function to identify lazy-free folios to improve
code readability.

Link: https://lkml.kernel.org/r/20260221093918.1456187-4-vernon2gm@gmail.com
Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Liam Howlett <Liam.Howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-04-05 13:53:03 -07:00
Lorenzo Stoakes (Oracle)
3a206a8649 mm/rmap: clear vma->anon_vma on error 
Commit 542eda1a83 ("mm/rmap: improve anon_vma_clone(),
unlink_anon_vmas() comments, add asserts") alters the way errors are
handled, but overlooked one important aspect of clean up.

When a VMA encounters an error state in anon_vma_clone() (that is, on
attempted allocation of anon_vma_chain objects), it cleans up partially
established state in cleanup_partial_anon_vmas(), before returning an
error.

However, this occurs prior to anon_vma->num_active_vmas being incremented,
and it also fails to clear the VMA's vma->anon_vma field, which remains in
place.

This is immediately an inconsistent state, because
anon_vma->num_active_vmas is supposed to track the number of VMAs whose
vma->anon_vma field references that anon_vma, and now that count is
off-by-negative-1 for each VMA for which this error state has occurred.

When VMAs are unlinked from this anon_vma, unlink_anon_vmas() will
eventually underflow anon_vma->num_active_vmas, which will trigger a
warning.

This will always eventually happen, as we unlink anon_vma's at process
teardown.

It could also cause maybe_reuse_anon_vma() to incorrectly permit the reuse
of an anon_vma which has active VMAs attached, which will lead to a
persistently invalid state.

The solution is to clear the VMA's anon_vma field when we clean up partial
state, as the fact we are doing so indicates clearly that the VMA is not
correctly integrated into the anon_vma tree and thus this field is
invalid.

Link: https://lkml.kernel.org/r/20260318122632.63404-1-ljs@kernel.org
Fixes: 542eda1a83 ("mm/rmap: improve anon_vma_clone(), unlink_anon_vmas() comments, add asserts")
Signed-off-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Reported-by: Sasha Levin <sashal@kernel.org>
Closes: https://lore.kernel.org/linux-mm/20260302151547.2389070-1-sashal@kernel.org/
Reported-by: Jiakai Xu <jiakaipeanut@gmail.com>
Closes: https://lore.kernel.org/linux-mm/CAFb8wJvRhatRD-9DVmr5v5pixTMPEr3UKjYBJjCd09OfH55CKg@mail.gmail.com/
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Tested-by: Jiakai Xu <jiakaipeanut@gmail.com>
Acked-by: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Sasha Levin (Microsoft) <sashal@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-21 17:36:33 -07:00
Wei Yang
939080834f mm/huge_memory: fix early failure try_to_migrate() when split huge pmd for shared THP 
Commit 60fbb14396 ("mm/huge_memory: adjust try_to_migrate_one() and
split_huge_pmd_locked()") return false unconditionally after
split_huge_pmd_locked().  This may fail try_to_migrate() early when
TTU_SPLIT_HUGE_PMD is specified.

The reason is the above commit adjusted try_to_migrate_one() to, when a
PMD-mapped THP entry is found, and TTU_SPLIT_HUGE_PMD is specified (for
example, via unmap_folio()), return false unconditionally.  This breaks
the rmap walk and fail try_to_migrate() early, if this PMD-mapped THP is
mapped in multiple processes.

The user sensible impact of this bug could be:

  * On memory pressure, shrink_folio_list() may split partially mapped
    folio with split_folio_to_list(). Then free unmapped pages without IO.
    If failed, it may not be reclaimed.
  * On memory failure, memory_failure() would call try_to_split_thp_page()
    to split folio contains the bad page. If succeed, the PG_has_hwpoisoned
    bit is only set in the after-split folio contains @split_at. By doing
    so, we limit bad memory. If failed to split, the whole folios is not
    usable.

One way to reproduce:

    Create an anonymous THP range and fork 512 children, so we have a
    THP shared mapped in 513 processes. Then trigger folio split with
    /sys/kernel/debug/split_huge_pages debugfs to split the THP folio to
    order 0.

Without the above commit, we can successfully split to order 0.  With the
above commit, the folio is still a large folio.

And currently there are two core users of TTU_SPLIT_HUGE_PMD:

  * try_to_unmap_one()
  * try_to_migrate_one()

try_to_unmap_one() would restart the rmap walk, so only
try_to_migrate_one() is affected.

We can't simply revert commit 60fbb14396 ("mm/huge_memory: adjust
try_to_migrate_one() and split_huge_pmd_locked()"), since it removed some
duplicated check covered by page_vma_mapped_walk().

This patch fixes this by restart page_vma_mapped_walk() after
split_huge_pmd_locked().  Since we cannot simply return "true" to fix the
problem, as that would affect another case:

    When invoking folio_try_share_anon_rmap_pmd() from
    split_huge_pmd_locked(), the latter can fail and leave a large folio
    mapped through PTEs, in which case we ought to return true from
    try_to_migrate_one(). This might result in unnecessary walking of the
    rmap but is relatively harmless.

Link: https://lkml.kernel.org/r/20260305015006.27343-1-richard.weiyang@gmail.com
Fixes: 60fbb14396 ("mm/huge_memory: adjust try_to_migrate_one() and split_huge_pmd_locked()")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Tested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Gavin Guo <gavinguo@igalia.com>
Acked-by: David Hildenbrand (arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-10 16:01:49 -07:00
Dev Jain
29f40594a2 mm/rmap: fix incorrect pte restoration for lazyfree folios 
We batch unmap anonymous lazyfree folios by folio_unmap_pte_batch.  If the
batch has a mix of writable and non-writable bits, we may end up setting
the entire batch writable.  Fix this by respecting writable bit during
batching.

Although on a successful unmap of a lazyfree folio, the soft-dirty bit is
lost, preserve it on pte restoration by respecting the bit during
batching, to make the fix consistent w.r.t both writable bit and
soft-dirty bit.

I was able to write the below reproducer and crash the kernel. 
Explanation of reproducer (set 64K mTHP to always):

Fault in a 64K large folio.  Split the VMA at mid-point with
MADV_DONTFORK.  fork() - parent points to the folio with 8 writable ptes
and 8 non-writable ptes.  Merge the VMAs with MADV_DOFORK so that
folio_unmap_pte_batch() can determine all the 16 ptes as a batch.  Do
MADV_FREE on the range to mark the folio as lazyfree.  Write to the memory
to dirty the pte, eventually rmap will dirty the folio.  Then trigger
reclaim, we will hit the pte restoration path, and the kernel will crash
with the trace given below.

The BUG happens at:

	BUG_ON(atomic_inc_return(&ptc->anon_map_count) > 1 && rw);

The code path is asking for anonymous page to be mapped writable into the
pagetable.  The BUG_ON() firing implies that such a writable page has been
mapped into the pagetables of more than one process, which breaks
anonymous memory/CoW semantics.

[   21.134473] kernel BUG at mm/page_table_check.c:118!
[   21.134497] Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
[   21.135917] Modules linked in:
[   21.136085] CPU: 1 UID: 0 PID: 1735 Comm: dup-lazyfree Not tainted 7.0.0-rc1-00116-g018018a17770 #1028 PREEMPT
[   21.136858] Hardware name: linux,dummy-virt (DT)
[   21.137019] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
[   21.137308] pc : page_table_check_set+0x28c/0x2a8
[   21.137607] lr : page_table_check_set+0x134/0x2a8
[   21.137885] sp : ffff80008a3b3340
[   21.138124] x29: ffff80008a3b3340 x28: fffffdffc3d14400 x27: ffffd1a55e03d000
[   21.138623] x26: 0040000000000040 x25: ffffd1a55f7dd000 x24: 0000000000000001
[   21.139045] x23: 0000000000000001 x22: 0000000000000001 x21: ffffd1a55f217f30
[   21.139629] x20: 0000000000134521 x19: 0000000000134519 x18: 005c43e000040000
[   21.140027] x17: 0001400000000000 x16: 0001700000000000 x15: 000000000000ffff
[   21.140578] x14: 000000000000000c x13: 005c006000000000 x12: 0000000000000020
[   21.140828] x11: 0000000000000000 x10: 005c000000000000 x9 : ffffd1a55c079ee0
[   21.141077] x8 : 0000000000000001 x7 : 005c03e000040000 x6 : 000000004000ffff
[   21.141490] x5 : ffff00017fffce00 x4 : 0000000000000001 x3 : 0000000000000002
[   21.141741] x2 : 0000000000134510 x1 : 0000000000000000 x0 : ffff0000c08228c0
[   21.141991] Call trace:
[   21.142093]  page_table_check_set+0x28c/0x2a8 (P)
[   21.142265]  __page_table_check_ptes_set+0x144/0x1e8
[   21.142441]  __set_ptes_anysz.constprop.0+0x160/0x1a8
[   21.142766]  contpte_set_ptes+0xe8/0x140
[   21.142907]  try_to_unmap_one+0x10c4/0x10d0
[   21.143177]  rmap_walk_anon+0x100/0x250
[   21.143315]  try_to_unmap+0xa0/0xc8
[   21.143441]  shrink_folio_list+0x59c/0x18a8
[   21.143759]  shrink_lruvec+0x664/0xbf0
[   21.144043]  shrink_node+0x218/0x878
[   21.144285]  __node_reclaim.constprop.0+0x98/0x338
[   21.144763]  user_proactive_reclaim+0x2a4/0x340
[   21.145056]  reclaim_store+0x3c/0x60
[   21.145216]  dev_attr_store+0x20/0x40
[   21.145585]  sysfs_kf_write+0x84/0xa8
[   21.145835]  kernfs_fop_write_iter+0x130/0x1c8
[   21.145994]  vfs_write+0x2b8/0x368
[   21.146119]  ksys_write+0x70/0x110
[   21.146240]  __arm64_sys_write+0x24/0x38
[   21.146380]  invoke_syscall+0x50/0x120
[   21.146513]  el0_svc_common.constprop.0+0x48/0xf8
[   21.146679]  do_el0_svc+0x28/0x40
[   21.146798]  el0_svc+0x34/0x110
[   21.146926]  el0t_64_sync_handler+0xa0/0xe8
[   21.147074]  el0t_64_sync+0x198/0x1a0
[   21.147225] Code: f9400441 b4fff241 17ffff94 d4210000 (d4210000)
[   21.147440] ---[ end trace 0000000000000000 ]---

#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <string.h>
#include <sys/wait.h>
#include <sched.h>
#include <fcntl.h>

void write_to_reclaim() {
    const char *path = "/sys/devices/system/node/node0/reclaim";
    const char *value = "409600000000";
    int fd = open(path, O_WRONLY);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    if (write(fd, value, sizeof("409600000000") - 1) == -1) {
        perror("write");
        close(fd);
        exit(EXIT_FAILURE);
    }

    printf("Successfully wrote %s to %s\n", value, path);
    close(fd);
}

int main()
{
	char *ptr = mmap((void *)(1UL << 30), 1UL << 16, PROT_READ | PROT_WRITE,
			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if ((unsigned long)ptr != (1UL << 30)) {
		perror("mmap");
		return 1;
	}

	/* a 64K folio gets faulted in */
	memset(ptr, 0, 1UL << 16);

	/* 32K half will not be shared into child */
	if (madvise(ptr, 1UL << 15, MADV_DONTFORK)) {
		perror("madvise madv dontfork");
		return 1;
	}

	pid_t pid = fork();

	if (pid < 0) {
		perror("fork");
		return 1;
	} else if (pid == 0) {
		sleep(15);
	} else {
		/* merge VMAs. now first half of the 16 ptes are writable, the other half not. */
		if (madvise(ptr, 1UL << 15, MADV_DOFORK)) {
			perror("madvise madv fork");
			return 1;
		}
		if (madvise(ptr, (1UL << 16), MADV_FREE)) {
			perror("madvise madv free");
			return 1;
		}

		/* dirty the large folio */
		(*ptr) += 10;

		write_to_reclaim();
		// sleep(10);
		waitpid(pid, NULL, 0);

	}
}

Link: https://lkml.kernel.org/r/20260303061528.2429162-1-dev.jain@arm.com
Fixes: 354dffd295 ("mm: support batched unmap for lazyfree large folios during reclamation")
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Tested-by: Lance Yang <lance.yang@linux.dev>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-03-10 16:01:49 -07:00
Baolin Wang
a67fe41e21 mm: rmap: support batched unmapping for file large folios 
Similar to folio_referenced_one(), we can apply batched unmapping for file
large folios to optimize the performance of file folios reclamation.

Barry previously implemented batched unmapping for lazyfree anonymous
large folios[1] and did not further optimize anonymous large folios or
file-backed large folios at that stage.  As for file-backed large folios,
the batched unmapping support is relatively straightforward, as we only
need to clear the consecutive (present) PTE entries for file-backed large
folios.

Note that it's not ready to support batched unmapping for uffd case, so
let's still fallback to per-page unmapping for the uffd case.

Performance testing:
Allocate 10G clean file-backed folios by mmap() in a memory cgroup, and
try to reclaim 8G file-backed folios via the memory.reclaim interface.  I
can observe 75% performance improvement on my Arm64 32-core server (and
50%+ improvement on my X86 machine) with this patch.

W/o patch:
real    0m1.018s
user    0m0.000s
sys     0m1.018s

W/ patch:
real	0m0.249s
user	0m0.000s
sys	0m0.249s

[1] https://lore.kernel.org/all/20250214093015.51024-4-21cnbao@gmail.com/T/#u
Link: https://lkml.kernel.org/r/b53a16f67c93a3fe65e78092069ad135edf00eff.1770645603.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: Barry Song <baohua@kernel.org>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-02-12 15:43:01 -08:00
Baolin Wang
52e054f718 mm: rmap: support batched checks of the references for large folios 
Patch series "support batch checking of references and unmapping for large
folios", v6.


Currently, folio_referenced_one() always checks the young flag for each
PTE sequentially, which is inefficient for large folios.  This
inefficiency is especially noticeable when reclaiming clean file-backed
large folios, where folio_referenced() is observed as a significant
performance hotspot.

Moreover, on Arm architecture, which supports contiguous PTEs, there is
already an optimization to clear the young flags for PTEs within a
contiguous range.  However, this is not sufficient.  We can extend this to
perform batched operations for the entire large folio (which might exceed
the contiguous range: CONT_PTE_SIZE).

Similar to folio_referenced_one(), we can also apply batched unmapping for
large file folios to optimize the performance of file folio reclamation. 
By supporting batched checking of the young flags, flushing TLB entries,
and unmapping, I can observed a significant performance improvements in my
performance tests for file folios reclamation.  Please check the
performance data in the commit message of each patch.


This patch (of 5):

Currently, folio_referenced_one() always checks the young flag for each
PTE sequentially, which is inefficient for large folios.  This
inefficiency is especially noticeable when reclaiming clean file-backed
large folios, where folio_referenced() is observed as a significant
performance hotspot.

Moreover, on Arm64 architecture, which supports contiguous PTEs, there is
already an optimization to clear the young flags for PTEs within a
contiguous range.  However, this is not sufficient.  We can extend this to
perform batched operations for the entire large folio (which might exceed
the contiguous range: CONT_PTE_SIZE).

Introduce a new API: clear_flush_young_ptes() to facilitate batched
checking of the young flags and flushing TLB entries, thereby improving
performance during large folio reclamation.  And it will be overridden by
the architecture that implements a more efficient batch operation in the
following patches.

While we are at it, rename ptep_clear_flush_young_notify() to
clear_flush_young_ptes_notify() to indicate that this is a batch
operation.

Link: https://lkml.kernel.org/r/cover.1770645603.git.baolin.wang@linux.alibaba.com
Link: https://lkml.kernel.org/r/12132694536834262062d1fb304f8f8a064b6750.1770645603.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Cc: Barry Song <baohua@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-02-12 15:43:00 -08:00
Tim Bird
ef24e0aa07 mm: add SPDX id lines to some mm source files 
Some of the memory management source files are missing
SPDX-License-Identifier lines.  Add appropriate IDs
to these files (mostly GPL-2.0, but one LGPL-2.1).

Link: https://lkml.kernel.org/r/20260204213101.1754183-1-tim.bird@sony.com
Signed-off-by: Tim Bird <tim.bird@sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-02-06 15:47:16 -08:00
Kairui Song
3697615914 mm, swap: cleanup swap entry management workflow 
The current swap entry allocation/freeing workflow has never had a clear
definition.  This makes it hard to debug or add new optimizations.

This commit introduces a proper definition of how swap entries would be
allocated and freed.  Now, most operations are folio based, so they will
never exceed one swap cluster, and we now have a cleaner border between
swap and the rest of mm, making it much easier to follow and debug,
especially with new added sanity checks.  Also making more optimization
possible.

Swap entry will be mostly freed and free with a folio bound.  The folio
lock will be useful for resolving many swap related races.

Now swap allocation (except hibernation) always starts with a folio in the
swap cache, and gets duped/freed protected by the folio lock:

- folio_alloc_swap() - The only allocation entry point now.
  Context: The folio must be locked.
  This allocates one or a set of continuous swap slots for a folio and
  binds them to the folio by adding the folio to the swap cache. The
  swap slots' swap count start with zero value.

- folio_dup_swap() - Increase the swap count of one or more entries.
  Context: The folio must be locked and in the swap cache. For now, the
  caller still has to lock the new swap entry owner (e.g., PTL).
  This increases the ref count of swap entries allocated to a folio.
  Newly allocated swap slots' count has to be increased by this helper
  as the folio got unmapped (and swap entries got installed).

- folio_put_swap() - Decrease the swap count of one or more entries.
  Context: The folio must be locked and in the swap cache. For now, the
  caller still has to lock the new swap entry owner (e.g., PTL).
  This decreases the ref count of swap entries allocated to a folio.
  Typically, swapin will decrease the swap count as the folio got
  installed back and the swap entry got uninstalled

  This won't remove the folio from the swap cache and free the
  slot. Lazy freeing of swap cache is helpful for reducing IO.
  There is already a folio_free_swap() for immediate cache reclaim.
  This part could be further optimized later.

The above locking constraints could be further relaxed when the swap table
is fully implemented.  Currently dup still needs the caller to lock the
swap entry container (e.g.  PTL), or a concurrent zap may underflow the
swap count.

Some swap users need to interact with swap count without involving folio
(e.g.  forking/zapping the page table or mapping truncate without swapin).
In such cases, the caller has to ensure there is no race condition on
whatever owns the swap count and use the below helpers:

- swap_put_entries_direct() - Decrease the swap count directly.
  Context: The caller must lock whatever is referencing the slots to
  avoid a race.

  Typically the page table zapping or shmem mapping truncate will need
  to free swap slots directly. If a slot is cached (has a folio bound),
  this will also try to release the swap cache.

- swap_dup_entry_direct() - Increase the swap count directly.
  Context: The caller must lock whatever is referencing the entries to
  avoid race, and the entries must already have a swap count > 1.

  Typically, forking will need to copy the page table and hence needs to
  increase the swap count of the entries in the table. The page table is
  locked while referencing the swap entries, so the entries all have a
  swap count > 1 and can't be freed.

Hibernation subsystem is a bit different, so two special wrappers are here:

- swap_alloc_hibernation_slot() - Allocate one entry from one device.
- swap_free_hibernation_slot() - Free one entry allocated by the above
  helper.

All hibernation entries are exclusive to the hibernation subsystem and
should not interact with ordinary swap routines.

By separating the workflows, it will be possible to bind folio more
tightly with swap cache and get rid of the SWAP_HAS_CACHE as a temporary
pin.

This commit should not introduce any behavior change

[kasong@tencent.com: fix leak, per Chris Mason.  Remove WARN_ON, per Lai Yi]
  Link: https://lkml.kernel.org/r/CAMgjq7AUz10uETVm8ozDWcB3XohkOqf0i33KGrAquvEVvfp5cg@mail.gmail.com
[ryncsn@gmail.com: fix KSM copy pages for swapoff, per Chris]
  Link: https://lkml.kernel.org/r/aXxkANcET3l2Xu6J@KASONG-MC4
Link: https://lkml.kernel.org/r/20251220-swap-table-p2-v5-14-8862a265a033@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Signed-off-by: Kairui Song <ryncsn@gmail.com>
Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: Deepanshu Kartikey <kartikey406@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Chris Mason <clm@fb.com>
Cc: Chris Mason <clm@meta.com>
Cc: Lai Yi <yi1.lai@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-31 14:22:56 -08:00
Lorenzo Stoakes
d17f02417a mm/rmap: separate out fork-only logic on anon_vma_clone() 
Specify which operation is being performed to anon_vma_clone(), which
allows us to do checks specific to each operation type, as well as to
separate out and make clear that the anon_vma reuse logic is absolutely
specific to fork only.

This opens the door to further refactorings and refinements later as we
have more information to work with.

Link: https://lkml.kernel.org/r/cf7da7a2d973cdc72a1b80dd9a73260519e8fa9f.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:22 -08:00
Lorenzo Stoakes
bfc2b13b05 mm/rmap: allocate anon_vma_chain objects unlocked when possible 
There is no reason to allocate the anon_vma_chain under the anon_vma write
lock when cloning - we can in fact assign these to the destination VMA
safely as we hold the exclusive mmap lock and therefore preclude anybody
else accessing these fields.

We only need take the anon_vma write lock when we link rbtree edges from
the anon_vma to the newly established AVCs.

This also allows us to eliminate the weird GFP_NOWAIT, GFP_KERNEL dance
introduced in commit dd34739c03 ("mm: avoid anon_vma_chain allocation
under anon_vma lock"), further simplifying this logic.

This should reduce lock anon_vma contention, and clarifies exactly where
the anon_vma lock is required.

We cannot adjust __anon_vma_prepare() in the same way as this is only
protected by VMA read lock, so we have to perform the allocation here
under the anon_vma write lock and page_table_lock (to protect against
racing threads), and we wish to retain the lock ordering.

With this change we can simplify cleanup_partial_anon_vmas() even further
- since we allocate AVC's without any lock taken and do not insert
anything into the interval tree until after the allocations are tried, we
can remove all logic pertaining to this and just free up AVC's only.

Link: https://lkml.kernel.org/r/624bf1ac0bde4871fcfca2c8c8e294b6d8f7ae7b.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:22 -08:00
Lorenzo Stoakes
535f6b8df1 mm/rmap: remove unnecessary root lock dance in anon_vma clone, unmap 
The root anon_vma of all anon_vma's linked to a VMA must by definition be
the same - a VMA and all of its descendants/ancestors must exist in the
same CoW chain.

Commit bb4aa39676 ("mm: avoid repeated anon_vma lock/unlock sequences in
anon_vma_clone()") introduced paranoid checking of the root anon_vma
remaining the same throughout all AVC's in 2011.

I think 15 years later we can safely assume that this is always the case.

Additionally, since unfaulted VMAs being cloned from or unlinked are
no-op's, we can simply lock the anon_vma's associated with this rather
than doing any specific dance around this.

This removes unnecessary checks and makes it clear that the root anon_vma
is shared between all anon_vma's in a given VMA's anon_vma_chain.

Link: https://lkml.kernel.org/r/838030d2f0772b99fa99ff4b4fd571353f14a1a9.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:21 -08:00
Lorenzo Stoakes
69e9458455 mm/rmap: skip unfaulted VMAs on anon_vma clone, unlink 
For both anon_vma_clone() and unlink_anon_vmas(), if the source VMA or the
VMA to be linked are unfaulted (e.g.  !vma->anon_vma), then the functions
do nothing.  Simply exit early in these cases.

In the unlink_anon_vmas() case we can also remove a conditional that
checks whether vma->anon_vma is set.

Link: https://lkml.kernel.org/r/085a25f7528e1c8c687276e9b856e88dc8f105ca.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:21 -08:00
Lorenzo Stoakes
91901a441f mm/rmap: eliminate partial anon_vma tear-down in anon_vma_fork() 
We have spun a web of unnecessary headaches for ourselves in
anon_vma_fork() with the introduction of the anon_vma reuse logic, as
introduced by commit 7a3ef208e6 ("mm: prevent endless growth of anon_vma
hierarchy").

When we clone anon_vma's linked to a VMA via vma->anon_vma_chain, we check
each anon_vma for specific conditions, and if met we set vma->anon_vma to
this anon_vma to indicate we will reuse it rather than allocating a new
one.

It triggers upon the first ancestor anon_vma found that possesses at most
1 child, and no active VMAs.

This was implemented such that if you continually fork and free VMAs, you
would achieve anon_vma reuse rather than continually allocating
unnecessary new anon_vma's.

This however brings an unfortunate situation should a memory allocation
fail during this process.  anon_vma_fork():

1. Clones the anon_vma.
2. If no reuse (i.e. !vma->anon_vma), tries to allocate anon_vma, AVC.
3. If 2 fails, we are forced to unwind step 1 by invoking
   unlink_anon_vmas(vma).

This means that we send a partially set up (i.e.  invalid) VMA to
unlink_anon_vmas().

Doing this is dangerous and confusing - it is reasonable for kernel
developers to assume unlink_anon_vmas() is called on a correctly
established vma, and thus confusion arises if logic is implemented there
to account for invalid VMAs, and further development might introduce
subtle bugs.

It is especially problematic in the anon rmap implementation which is
essentially a broken abstraction.

The patch solves the issue by simply trying to allocate the anon_vma and
AVC ahead of time - i.e.  optimising for the usual case - and freeing them
should reuse occur or an error arise in anon_vma_clone().

This is not egregious performance-wise, as this function is called on the
fork path which already performs a great number of allocations, and thus
it is already a slow-path in this respect.

It is additionally not egregious in terms of memory usage - the
allocations are too-small-to-fail anyway unless, for instance, a fatal
signal may have arisen, and any OOM for such tiny allocations that may
arise would indicate the system is under so much memory pressure that the
associated process is not long for this world anyway.

We also update anon_vma->num_active_vmas to 1 directly rather than
incrementing the newly allocated anon_vma's active VMA count - this makes
it clear that this detached anon_vma can have only 1 num_active_vma at
this point.

Finally we eliminate the out_error and out_error_free_anon_vma labels
which makes the logic much easier to follow.  We also correct a small
comment typo.

Link: https://lkml.kernel.org/r/9923da5f8b095dd1e8d677692dcaf95859de0ef5.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:20 -08:00
Lorenzo Stoakes
542eda1a83 mm/rmap: improve anon_vma_clone(), unlink_anon_vmas() comments, add asserts 
Patch series "mm: clean up anon_vma implementation", v3.

The anon_vma logic is hugely confusing and, much like a bundle of wires
entangled with one another, pulling on one thread seems only to lead to
more entanglement elsewhere.

There is a mish-mash of the core implementation, how that implementation
is invoked, how helper functions are invoked and concepts such as adjacent
anon_vma merge and anon_vma object reuse.

This series tries to improve the situation somewhat.

It starts by establishing some invariants in the core anon_vma_clone() and
unlink_anon_vmas() functions, largely expressed via VM_WARN_ON_ONCE()
asserts.

These act as some form of self-documentation as to the conditions we find
ourselves in when invoking these functions.

We also add kdoc comments for anon_vma_clone() and unlink_anon_vmas().

We then update anon_vma_fork() to avoid passing a partially set up (and
thus invalid) VMA to unlink_anon_vmas() - functions which are used both
for partially set up and valid data types has historically been the source
of a lot of confusion and bugs.

We then makes use of the established known conditions to directly skip
unfaulted VMAs (rather than implicitly via an empty vma->anon_vma_chain
list).

We remove the confusing anon_vma_merge() function (we already have a
concept of anon_vma merge in that we merge anon_vma's that would otherwise
be compatible except for attributes that mprotect() could change - which
anon_vma_merge() has nothing to do with).

We make the anon_vma functions internal to mm as they do not need to be
used by any other part of the kernel, which allows for future abstraction
without concern about this.

We then reduce the time over which we hold the anon rmap lock in
anon_vma_clone(), as it turns out we can allocate anon_vma_chain objects
without holding this lock, since the objects are not yet accessible from
the rmap.

This should reduce anon_vma lock contention.

This additionally allows us to remove a confusing GFP_NOWAIT, GFP_KERNEL
allocation fallback strategy.

Finally, we explicitly indicate which operation is being performed upon
anon_vma_clone(), and separate out fork-only logic to make it very clear
that anon_vma reuse only occurs on fork.


This patch (of 9):

Add kdoc comments and describe exactly what these functions are used for
in detail, pointing out importantly that the anon_vma_clone()
!dst->anon_vma && src->anon_vma dance is ONLY for fork.

Both are confusing functions that will be refactored in a subsequent patch
but the first stage is establishing documentation and some invariants.

Add some basic CONFIG_DEBUG_VM asserts that help document expected state,
specifically:

anon_vma_clone()
- mmap write lock held.
- We do nothing if src VMA is not faulted.
- The destination VMA has no anon_vma_chain yet.
- We are always operating on the same active VMA (i.e. vma->anon_vma).
- If not forking, must operate on the same mm_struct.

unlink_anon_vmas()
- mmap lock held (write lock except when freeing page tables).
- That unfaulted VMAs are no-ops.

We are presented with a special case when anon_vma_clone() fails to
allocate memory, where we have a VMA with partially set up anon_vma state.
Since we hold the exclusive mmap write lock, and since we are cloning
from a source VMA which consequently can't also have its anon_vma state
modified, we know no anon_vma referenced can be empty.

This allows us to significantly simplify this case and just remove
anon_vma_chain objects associated with the VMA, so we add a specific
partial cleanup path for this scenario.

This also allows us to drop the hack of setting vma->anon_vma to NULL
before unlinking anon_vma state in this scenario.

Link: https://lkml.kernel.org/r/cover.1768746221.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/8644e89369be0cc89d7ac57443dff9e822803c91.1768746221.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chriscli@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-26 20:02:20 -08:00
David Hildenbrand (Red Hat)
8ce720d5bd mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather 
As reported, ever since commit 1013af4f58 ("mm/hugetlb: fix
huge_pmd_unshare() vs GUP-fast race") we can end up in some situations
where we perform so many IPI broadcasts when unsharing hugetlb PMD page
tables that it severely regresses some workloads.

In particular, when we fork()+exit(), or when we munmap() a large
area backed by many shared PMD tables, we perform one IPI broadcast per
unshared PMD table.

There are two optimizations to be had:

(1) When we process (unshare) multiple such PMD tables, such as during
    exit(), it is sufficient to send a single IPI broadcast (as long as
    we respect locking rules) instead of one per PMD table.

    Locking prevents that any of these PMD tables could get reused before
    we drop the lock.

(2) When we are not the last sharer (> 2 users including us), there is
    no need to send the IPI broadcast. The shared PMD tables cannot
    become exclusive (fully unshared) before an IPI will be broadcasted
    by the last sharer.

    Concurrent GUP-fast could walk into a PMD table just before we
    unshared it. It could then succeed in grabbing a page from the
    shared page table even after munmap() etc succeeded (and supressed
    an IPI). But there is not difference compared to GUP-fast just
    sleeping for a while after grabbing the page and re-enabling IRQs.

    Most importantly, GUP-fast will never walk into page tables that are
    no-longer shared, because the last sharer will issue an IPI
    broadcast.

    (if ever required, checking whether the PUD changed in GUP-fast
     after grabbing the page like we do in the PTE case could handle
     this)

So let's rework PMD sharing TLB flushing + IPI sync to use the mmu_gather
infrastructure so we can implement these optimizations and demystify the
code at least a bit. Extend the mmu_gather infrastructure to be able to
deal with our special hugetlb PMD table sharing implementation.

To make initialization of the mmu_gather easier when working on a single
VMA (in particular, when dealing with hugetlb), provide
tlb_gather_mmu_vma().

We'll consolidate the handling for (full) unsharing of PMD tables in
tlb_unshare_pmd_ptdesc() and tlb_flush_unshared_tables(), and track
in "struct mmu_gather" whether we had (full) unsharing of PMD tables.

Because locking is very special (concurrent unsharing+reuse must be
prevented), we disallow deferring flushing to tlb_finish_mmu() and instead
require an explicit earlier call to tlb_flush_unshared_tables().

From hugetlb code, we call huge_pmd_unshare_flush() where we make sure
that the expected lock protecting us from concurrent unsharing+reuse is
still held.

Check with a VM_WARN_ON_ONCE() in tlb_finish_mmu() that
tlb_flush_unshared_tables() was properly called earlier.

Document it all properly.

Notes about tlb_remove_table_sync_one() interaction with unsharing:

There are two fairly tricky things:

(1) tlb_remove_table_sync_one() is a NOP on architectures without
    CONFIG_MMU_GATHER_RCU_TABLE_FREE.

    Here, the assumption is that the previous TLB flush would send an
    IPI to all relevant CPUs. Careful: some architectures like x86 only
    send IPIs to all relevant CPUs when tlb->freed_tables is set.

    The relevant architectures should be selecting
    MMU_GATHER_RCU_TABLE_FREE, but x86 might not do that in stable
    kernels and it might have been problematic before this patch.

    Also, the arch flushing behavior (independent of IPIs) is different
    when tlb->freed_tables is set. Do we have to enlighten them to also
    take care of tlb->unshared_tables? So far we didn't care, so
    hopefully we are fine. Of course, we could be setting
    tlb->freed_tables as well, but that might then unnecessarily flush
    too much, because the semantics of tlb->freed_tables are a bit
    fuzzy.

    This patch changes nothing in this regard.

(2) tlb_remove_table_sync_one() is not a NOP on architectures with
    CONFIG_MMU_GATHER_RCU_TABLE_FREE that actually don't need a sync.

    Take x86 as an example: in the common case (!pv, !X86_FEATURE_INVLPGB)
    we still issue IPIs during TLB flushes and don't actually need the
    second tlb_remove_table_sync_one().

    This optimized can be implemented on top of this, by checking e.g., in
    tlb_remove_table_sync_one() whether we really need IPIs. But as
    described in (1), it really must honor tlb->freed_tables then to
    send IPIs to all relevant CPUs.

Notes on TLB flushing changes:

(1) Flushing for non-shared PMD tables

    We're converting from flush_hugetlb_tlb_range() to
    tlb_remove_huge_tlb_entry(). Given that we properly initialize the
    MMU gather in tlb_gather_mmu_vma() to be hugetlb aware, similar to
    __unmap_hugepage_range(), that should be fine.

(2) Flushing for shared PMD tables

    We're converting from various things (flush_hugetlb_tlb_range(),
    tlb_flush_pmd_range(), flush_tlb_range()) to tlb_flush_pmd_range().

    tlb_flush_pmd_range() achieves the same that
    tlb_remove_huge_tlb_entry() would achieve in these scenarios.
    Note that tlb_remove_huge_tlb_entry() also calls
    __tlb_remove_tlb_entry(), however that is only implemented on
    powerpc, which does not support PMD table sharing.

    Similar to (1), tlb_gather_mmu_vma() should make sure that TLB
    flushing keeps on working as expected.

Further, note that the ptdesc_pmd_pts_dec() in huge_pmd_share() is not a
concern, as we are holding the i_mmap_lock the whole time, preventing
concurrent unsharing. That ptdesc_pmd_pts_dec() usage will be removed
separately as a cleanup later.

There are plenty more cleanups to be had, but they have to wait until
this is fixed.

[david@kernel.org: fix kerneldoc]
  Link: https://lkml.kernel.org/r/f223dd74-331c-412d-93fc-69e360a5006c@kernel.org
Link: https://lkml.kernel.org/r/20251223214037.580860-5-david@kernel.org
Fixes: 1013af4f58 ("mm/hugetlb: fix huge_pmd_unshare() vs GUP-fast race")
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reported-by: Uschakow, Stanislav" <suschako@amazon.de>
Closes: https://lore.kernel.org/all/4d3878531c76479d9f8ca9789dc6485d@amazon.de/
Tested-by: Laurence Oberman <loberman@redhat.com>
Acked-by: Harry Yoo <harry.yoo@oracle.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-20 09:34:26 -08:00
David Hildenbrand (Red Hat)
a8682d500f mm/rmap: fix two comments related to huge_pmd_unshare() 
PMD page table unsharing no longer touches the refcount of a PMD page
table.  Also, it is not about dropping the refcount of a "PMD page" but
the "PMD page table".

Let's just simplify by saying that the PMD page table was unmapped,
consequently also unmapping the folio that was mapped into this page.

This code should be deduplicated in the future.

Link: https://lkml.kernel.org/r/20251223214037.580860-4-david@kernel.org
Fixes: 59d9094df3 ("mm: hugetlb: independent PMD page table shared count")
Signed-off-by: David Hildenbrand (Red Hat) <david@kernel.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Tested-by: Laurence Oberman <loberman@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Cc: Liu Shixin <liushixin2@huawei.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: "Uschakow, Stanislav" <suschako@amazon.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2026-01-20 09:34:26 -08:00
Shakeel Butt
c1bd09994c memcg: remove __lruvec_stat_mod_folio 
__lruvec_stat_mod_folio() is already safe against irqs, so there is no
need to have a separate interface (i.e.  lruvec_stat_mod_folio) which
wraps calls to it with irq disabling and reenabling.  Let's rename
__lruvec_stat_mod_folio() to lruvec_stat_mod_folio().

Link: https://lkml.kernel.org/r/20251110232008.1352063-5-shakeel.butt@linux.dev
Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Acked-by: Roman Gushchin <roman.gushchin@linux.dev>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:54 -08:00
Lorenzo Stoakes
a3a3e215c9 mm: replace remaining pte_to_swp_entry() with softleaf_from_pte() 
There are straggler invocations of pte_to_swp_entry() lying around,
replace all of these with the software leaf entry equivalent -
softleaf_from_pte().

With those removed, eliminate pte_to_swp_entry() altogether.

No functional change intended.

Link: https://lkml.kernel.org/r/d8ee5ccefe4c42d7c4fe1a2e46f285ac40421cd3.1762812360.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:52 -08:00
Lorenzo Stoakes
93976a2034 mm: eliminate further swapops predicates 
Having converted so much of the code base to software leaf entries, we can
mop up some remaining cases.

We replace is_pfn_swap_entry(), pfn_swap_entry_to_page(),
is_writable_device_private_entry(), is_device_exclusive_entry(),
is_migration_entry(), is_writable_migration_entry(),
is_readable_migration_entry(), swp_offset_pfn() and pfn_swap_entry_folio()
with softleaf equivalents.

No functional change intended.

Link: https://lkml.kernel.org/r/956bc9c031604811c0070d2f4bf2f1373f230213.1762812360.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Wei Xu <weixugc@google.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:52 -08:00
Lorenzo Stoakes
0ac881efe1 mm: replace pmd_to_swp_entry() with softleaf_from_pmd() 
Introduce softleaf_from_pmd() to do the equivalent operation for PMDs that
softleaf_from_pte() fulfils, and cascade changes through code base
accordingly, introducing helpers as necessary.

We are then able to eliminate pmd_to_swp_entry(),
is_pmd_migration_entry(), is_pmd_device_private_entry() and
is_pmd_non_present_folio_entry().

This further establishes the use of leaf operations throughout the code
base and further establishes the foundations for eliminating
is_swap_pmd().

No functional change intended.

[lorenzo.stoakes@oracle.com: check writable, not readable/writable, per Vlastimil]
  Link: https://lkml.kernel.org/r/cd97b6ec-00f9-45a4-9ae0-8f009c212a94@lucifer.local
Link: https://lkml.kernel.org/r/3fb431699639ded8fdc63d2210aa77a38c8891f1.1762812360.git.lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reviewed-by: SeongJae Park <sj@kernel.org>\
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Mathew Brost <matthew.brost@intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Wei Xu <weixugc@google.com>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Yuanchu Xie <yuanchu@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:51 -08:00
Balbir Singh
65edfda6f3 mm/rmap: extend rmap and migration support device-private entries 
Add device-private THP support to reverse mapping infrastructure, enabling
proper handling during migration and walk operations.

The key changes are:
- add_migration_pmd()/remove_migration_pmd(): Handle device-private
  entries during folio migration and splitting
- page_vma_mapped_walk(): Recognize device-private THP entries during
  VMA traversal operations

This change supports folio splitting and migration operations on
device-private entries.

[balbirs@nvidia.com: fix override of entry in remove_migration_pmd]
  Link: https://lkml.kernel.org/r/20251114012153.2634497-2-balbirs@nvidia.com
[balbirs@nvidia.com: follow pattern used in remove_migration_pte()]
  Link: https://lkml.kernel.org/r/20251115002835.3515194-1-balbirs@nvidia.com
Link: https://lkml.kernel.org/r/20251001065707.920170-5-balbirs@nvidia.com
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:48 -08:00
Balbir Singh
d245f9b4ab mm/zone_device: support large zone device private folios 
Patch series "mm: support device-private THP", v7.

This patch series introduces support for Transparent Huge Page (THP)
migration in zone device-private memory.  The implementation enables
efficient migration of large folios between system memory and
device-private memory

Background

Current zone device-private memory implementation only supports PAGE_SIZE
granularity, leading to:
- Increased TLB pressure
- Inefficient migration between CPU and device memory

This series extends the existing zone device-private infrastructure to
support THP, leading to:
- Reduced page table overhead
- Improved memory bandwidth utilization
- Seamless fallback to base pages when needed

In my local testing (using lib/test_hmm) and a throughput test, the series
shows a 350% improvement in data transfer throughput and a 80% improvement
in latency

These patches build on the earlier posts by Ralph Campbell [1]

Two new flags are added in vma_migration to select and mark compound
pages.  migrate_vma_setup(), migrate_vma_pages() and
migrate_vma_finalize() support migration of these pages when
MIGRATE_VMA_SELECT_COMPOUND is passed in as arguments.

The series also adds zone device awareness to (m)THP pages along with
fault handling of large zone device private pages.  page vma walk and the
rmap code is also zone device aware.  Support has also been added for
folios that might need to be split in the middle of migration (when the
src and dst do not agree on MIGRATE_PFN_COMPOUND), that occurs when src
side of the migration can migrate large pages, but the destination has not
been able to allocate large pages.  The code supported and used
folio_split() when migrating THP pages, this is used when
MIGRATE_VMA_SELECT_COMPOUND is not passed as an argument to
migrate_vma_setup().

The test infrastructure lib/test_hmm.c has been enhanced to support THP
migration.  A new ioctl to emulate failure of large page allocations has
been added to test the folio split code path.  hmm-tests.c has new test
cases for huge page migration and to test the folio split path.  A new
throughput test has been added as well.

The nouveau dmem code has been enhanced to use the new THP migration
capability.  

mTHP support:

The patches hard code, HPAGE_PMD_NR in a few places, but the code has been
kept generic to support various order sizes.  With additional refactoring
of the code support of different order sizes should be possible.

The future plan is to post enhancements to support mTHP with a rough
design as follows:

1. Add the notion of allowable thp orders to the HMM based test driver
2. For non PMD based THP paths in migrate_device.c, check to see if
   a suitable order is found and supported by the driver
3. Iterate across orders to check the highest supported order for migration
4. Migrate and finalize

The mTHP patches can be built on top of this series, the key design
elements that need to be worked out are infrastructure and driver support
for multiple ordered pages and their migration.

HMM support for large folios was added in 10b9feee2d ("mm/hmm:
populate PFNs from PMD swap entry").


This patch (of 16)

Add routines to support allocation of large order zone device folios and
helper functions for zone device folios, to check if a folio is device
private and helpers for setting zone device data.

When large folios are used, the existing page_free() callback in pgmap is
called when the folio is freed, this is true for both PAGE_SIZE and higher
order pages.

Zone device private large folios do not support deferred split and scan
like normal THP folios.

Link: https://lkml.kernel.org/r/20251001065707.920170-1-balbirs@nvidia.com
Link: https://lkml.kernel.org/r/20251001065707.920170-2-balbirs@nvidia.com
Link: https://lore.kernel.org/linux-mm/20201106005147.20113-1-rcampbell@nvidia.com/ [1]
Signed-off-by: Balbir Singh <balbirs@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Lyude Paul <lyude@redhat.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: David Airlie <airlied@gmail.com>
Cc: Simona Vetter <simona@ffwll.ch>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Mika Penttilä <mpenttil@redhat.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Francois Dugast <francois.dugast@intel.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-24 15:08:47 -08:00
Lokesh Gidra
95b34d6648 mm: always call rmap_walk() on locked folios 
Patch series "Improve UFFDIO_MOVE scalability by removing anon_vma lock", v2.

Userfaultfd has a scalability issue in its UFFDIO_MOVE ioctl, which is
heavily used in Android as its java garbage collector uses it for
concurrent heap compaction.

The issue arises because UFFDIO_MOVE updates folio->mapping to an anon_vma
with a different root, in order to move the folio from a src VMA to dst
VMA.  It performs the operation with the folio locked, but this is
insufficient, because rmap_walk() can be performed on non-KSM anonymous
folios without folio lock.

This means that UFFDIO_MOVE has to acquire the anon_vma write lock of the
root anon_vma belonging to the folio it wishes to move.

This causes scalability bottleneck when multiple threads perform
UFFDIO_MOVE simultanously on distinct pages of the same src VMA.  In field
traces of arm64 android devices, we have observed janky user interactions
due to long (sometimes over ~50ms) uninterruptible sleeps on main UI
thread caused by anon_vma lock contention in UFFDIO_MOVE.  This is
particularly severe during the beginning of GC's compaction phase when it
is likely to have multiple threads involved.

This patch resolves the issue by removing the exception in rmap_walk() for
non-KSM anon folios by ensuring that all folios are locked during rmap
walk.  This is less problematic than it might seem, as the only major
caller which utilises this mode is shrink_active_list(), which is covered
in detail in the first patch of this series.

As a result of changing our approach to locking, we can remove all the
code that took steps to acquire an anon_vma write lock instead of a folio
lock.  This results in a significant simplification and scalability
improvement of the code (currently only in UFFDIO_MOVE).  Furthermore, as
a side-effect, folio_lock_anon_vma_read() gets simpler as we don't need to
worry that folio->mapping may have changed under us.


This patch (of 2):

Guarantee that rmap_walk() is called on locked folios so that threads
changing folio->mapping and folio->index for non-KSM anon folios can
serialize on fine-grained folio lock rather than anon_vma lock.  Other
folio types are already always locked before rmap_walk().  With this, we
are going from 'not necessarily' locking the non-KSM anon folio to
'definitely' locking it during rmap walks.

This patch is in preparation for removing anon_vma write-lock from
UFFDIO_MOVE.

With this patch, three functions are now expected to be called with a
locked folio.  To be careful of not missing any case, here is the
exhaustive list of all their callers.

1) rmap_walk() is called from:

a) folio_referenced()
b) damon_folio_mkold()
c) damon_folio_young()
d) page_idle_clear_pte_refs()
e) try_to_unmap()
f) try_to_migrate()
g) folio_mkclean()
h) remove_migration_ptes()

In the above list, first 4 are changed in this patch to try-lock non-KSM
anon folios, similar to other types of folios.  The remaining functions in
the list already hold folio lock when calling rmap_walk().

2) folio_lock_anon_vma_read() is called from following functions:

a) collect_procs_anon()
b) page_idle_clear_pte_refs()
c) damon_folio_mkold()
d) damon_folio_young()
e) folio_referenced()
f) try_to_unmap()
g) try_to_migrate()

All the functions in above list, except collect_procs_anon(), are covered
by the rmap_walk() list above.  For collect_procs_anon(), with
kill_procs_now() changed to take folio lock in this patch ensures that all
callers of folio_lock_anon_vma_read() now hold the lock.

3) folio_get_anon_vma() is called from following functions, all of which
   already hold the folio lock:

a) move_pages_huge_pmd()
b) __folio_split()
c) move_pages_ptes()
d) migrate_folio_unmap()
e) unmap_and_move_huge_page()

Functionally, this patch doesn't break the logic because rmap walkers
generally do some other check to see if what is expected to mapped did
happen so it's fine, or otherwise treat things as best-effort.

Among the 4 functions changed in this patch, folio_referenced() is the
only core-mm function, and is also frequently accessed.  To assess the
impact of locking non-KSM anon folios in
shrink_active_list()->folio_referenced() path, we performed an app cycle
test on an arm64 android device.  During the whole duration of the test
there were over 140k invocations of shrink_active_list(), out of which
over 29k had at least one non-KSM anon folio on which folio_referenced()
was called.  In none of these invocations folio_trylock() failed.

Of course, we now take a lock where we wouldn't previously have.  In the
past it would have had a major impact in causing a CoW write fault to copy
a page in do_wp_page(), as commit 09854ba94c ("mm: do_wp_page()
simplification") caused a failure to obtain folio lock to result in a page
copy even if one wasn't necessary.

However, since commit 6c287605fd ("mm: remember exclusively mapped
anonymous pages with PG_anon_exclusive"), and the introduction of the
folio anon exclusive flag, this issue is significantly mitigated.

The only case remaining that we might worry about from this perspective is
that of read-only folios immediately after fork where the anon exclusive
bit will not have been set yet.

We note however in the case of read-only just-forked folios that
wp_can_reuse_anon_folio() will notice the raised reference count
established by shrink_active_list() via isolate_lru_folios() and refuse to
reuse in any case, so this will in fact have no impact - the folio lock is
ultimately immaterial here.

All-in-all it appears that there is little opportunity for meaningful
negative impact from this change.

Link: https://lkml.kernel.org/r/20250923071019.775806-1-lokeshgidra@google.com
Link: https://lkml.kernel.org/r/20250923071019.775806-2-lokeshgidra@google.com
Signed-off-by: Lokesh Gidra <lokeshgidra@google.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Harry Yoo <harry.yoo@oracle.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Barry Song <baohua@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kalesh Singh <kaleshsingh@google.com>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
 2025-11-16 17:28:00 -08:00