The memmap_init_zone_device() function only initializes the migratetype of
the first pageblock of a compound page. If the compound page size exceeds
pageblock_nr_pages (e.g., 1GB hugepages with 2MB pageblocks), subsequent
pageblocks in the compound page remain uninitialized.
Move the migratetype initialization out of __init_zone_device_page() and
into a separate pageblock_migratetype_init_range() function. This
iterates over the entire PFN range of the memory, ensuring that all
pageblocks are correctly initialized.
Also remove the stale confusing comment about MEMINIT_HOTPLUG above the
migratetype setting since it is an obsolete relic from commit 966cf44f63
("mm: defer ZONE_DEVICE page initialization to the point where we init
pgmap") and no longer makes sense here.
Link: https://lore.kernel.org/20260428081855.1249045-6-songmuchun@bytedance.com
Fixes: c4386bd8ee ("mm/memremap: add ZONE_DEVICE support for compound pages")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
When vmemmap optimization is enabled for DAX, the nr_memmap_pages counter
in /proc/vmstat is incorrect. The current code always accounts for the
full, non-optimized vmemmap size, but vmemmap optimization reduces the
actual number of vmemmap pages by reusing tail pages. This causes the
system to overcount vmemmap usage, leading to inaccurate page statistics
in /proc/vmstat.
Fix this by introducing section_nr_vmemmap_pages(), which returns the
exact vmemmap page count for a given pfn range based on whether
optimization is in effect.
Link: https://lore.kernel.org/20260428081855.1249045-5-songmuchun@bytedance.com
Fixes: 15995a3524 ("mm: report per-page metadata information")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Currently, the memory hot-remove call chain -- arch_remove_memory(),
__remove_pages(), sparse_remove_section() and section_deactivate() -- does
not carry the struct dev_pagemap pointer. This prevents the lower levels
from knowing whether the section was originally populated with vmemmap
optimizations (e.g., DAX with vmemmap optimization enabled).
Without this information, we cannot call vmemmap_can_optimize() to
determine if the vmemmap pages were optimized. As a result, the vmemmap
page accounting during teardown will mistakenly assume a non-optimized
allocation, leading to incorrect memmap statistics.
To lay the groundwork for fixing the vmemmap page accounting, we need to
pass the @pgmap pointer down to the deactivation location. Plumb the
@pgmap argument through the APIs of arch_remove_memory(), __remove_pages()
and sparse_remove_section(), mirroring the corresponding *_activate()
paths.
Link: https://lore.kernel.org/20260428081855.1249045-4-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
In create_altmaps_and_memory_blocks(), when arch_add_memory() succeeds
with memmap_on_memory enabled, the vmemmap pages are allocated from
params.altmap. If create_memory_block_devices() subsequently fails, the
error path calls arch_remove_memory() with a NULL altmap instead of
params.altmap.
This is a bug that could lead to memory corruption. Since altmap is NULL,
vmemmap_free() falls back to freeing the vmemmap pages into the system
buddy allocator via free_pages() instead of the altmap.
arch_remove_memory() then immediately destroys the physical linear mapping
for this memory. This injects unowned pages into the buddy allocator,
causing machine checks or memory corruption if the system later attempts
to allocate and use those freed pages.
Fix this by passing params.altmap to arch_remove_memory() in the error
path.
Link: https://lore.kernel.org/20260428081855.1249045-3-songmuchun@bytedance.com
Fixes: 6b8f0798b8 ("mm/memory_hotplug: split memmap_on_memory requests across memblocks")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Reviewed-by: Georgi Djakov <georgi.djakov@oss.qualcomm.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: Fix vmemmap optimization accounting and initialization",
v8.
The series fixes several bugs in vmemmap optimization, mainly around
incorrect page accounting and memmap initialization in DAX and memory
hotplug paths. It also fixes pageblock migratetype initialization and
struct page initialization for ZONE_DEVICE compound pages.
Patches 1-4 fix vmemmap accounting issues. Patch 1 fixes an accounting
underflow in the section activation failure path by moving vmemmap page
accounting into the lower-level allocation and freeing helpers. Patch 2
fixes incorrect altmap passing in the memory hotplug error path. Patch 3
passes pgmap through memory deactivation paths so the teardown side can
determine whether vmemmap optimization was in effect. Patch 4 uses that
information to account the optimized DAX vmemmap size correctly.
Patches 5-6 fix initialization issues in mm/mm_init. One makes sure all
pageblocks in ZONE_DEVICE compound pages get their migratetype
initialized. The other fixes a case where DAX memory hotplug reuses an
unoptimized early-section memmap while compound_nr_pages() still assumes
vmemmap optimization, leaving tail struct pages uninitialized.
This patch (of 6):
In section_activate(), if populate_section_memmap() fails, the error
handling path calls section_deactivate() to roll back the state. This
causes a vmemmap accounting imbalance.
Since commit c3576889d8 ("mm: fix accounting of memmap pages"), memmap
pages are accounted for only after populate_section_memmap() succeeds.
However, the failure path unconditionally calls section_deactivate(),
which decreases the vmemmap count. Consequently, a failure in
populate_section_memmap() leads to an accounting underflow, incorrectly
reducing the system's tracked vmemmap usage.
Fix this more thoroughly by moving all accounting calls into the lower
level functions that actually perform the vmemmap allocation and freeing:
- populate_section_memmap() accounts for newly allocated vmemmap pages -
depopulate_section_memmap() unaccounts when vmemmap is freed
This ensures proper accounting in all code paths, including error handling
and early section cases.
Link: https://lore.kernel.org/20260428081855.1249045-1-songmuchun@bytedance.com
Link: https://lore.kernel.org/20260428081855.1249045-2-songmuchun@bytedance.com
Fixes: c3576889d8 ("mm: fix accounting of memmap pages")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador <osalvador@suse.de>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Liam R. Howlett <liam@infradead.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Joao Martins <joao.m.martins@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The original version of mremap_test (7df666253f26: "kselftests: vm: add
mremap tests") validated remapped contents byte-by-byte and printed a
mismatch index in case the bytes streams didn't match. That was rather
inefficient, especially also if the test passed.
Later, commit 7033c6cc96 ("selftests/mm: mremap_test: optimize execution
time from minutes to seconds using chunkwise memcmp") used memcmp() on
bigger chunks, to fallback to byte-wise scanning to detect the problematic
index only if it discovered a problem.
However, the implementation is overly complicated (e.g., get_sqrt() is
currently not optimal) and we don't really have to report the exact index:
whoever debugs the failing test can figure that out.
Let's simplify by just comparing both byte streams with memcmp() and not
detecting the exact failed index.
Link: https://lore.kernel.org/20260415044509.579428-1-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Reported-by: Sarthak Sharma <sarthak.sharma@arm.com>
Tested-by: Sarthak Sharma <sarthak.sharma@arm.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
When dev_dax_kmem_probe() partially succeeds (at least one range is
mapped) but a subsequent range fails request_mem_region() or
add_memory_driver_managed(), the probe silently continues, ultimately
returning success, but with the corresponding range resource NULL'ed out.
dev_dax_kmem_remove() iterates over all dax_device ranges regardless of if
the underlying resource exists. When remove_memory() is called later, it
returns 0 because the memory was never added which causes
dev_dax_kmem_remove() to incorrectly assume the (nonexistent) resource can
be removed and attempts cleanup on a NULL pointer.
Fix this by skipping these ranges altogether, noting that these cases are
considered success, such that the cleanup is still reached when all
actually-added ranges are successfully removed.
Link: https://lore.kernel.org/20260223201516.1517657-1-dave@stgolabs.net
Fixes: 60e93dc097 ("device-dax: add dis-contiguous resource support")
Signed-off-by: Davidlohr Bueso <dave@stgolabs.net>
Reviewed-by: Ben Cheatham <benjamin.cheatham@amd.com>
Reviewed-by: Alison Schofield <alison.schofield@intel.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
%pGg produces nice readable output and decouples the format string from
the size of gfp_t.
Link: https://lore.kernel.org/20260326-gfp64-v2-4-d916021cecdf@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Acked-by: Allison Henderson <achender@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Allison Collins <allison.henderson@oracle.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislaw Gruszka <stf_xl@wp.pl>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
%pGg produces nice readable output and decouples the format string from
the size of gfp_t.
Link: https://lore.kernel.org/20260326-gfp64-v2-3-d916021cecdf@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Allison Collins <allison.henderson@oracle.com>
Cc: Allison Henderson <achender@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislaw Gruszka <stf_xl@wp.pl>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "treewide: fixup gfp_t printks", v2.
Use vprintf()'s special gfp_t conversion in a few places.
This patch (of 3):
%pGg produces nice readable output and decouples the format string from
the size of gfp_t.
Link: https://lore.kernel.org/20260326-gfp64-v2-0-d916021cecdf@google.com
Link: https://lore.kernel.org/20260326-gfp64-v2-1-d916021cecdf@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Allison Collins <allison.henderson@oracle.com>
Cc: Allison Henderson <achender@kernel.org>
Cc: Dave Airlie <airlied@gmail.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kacinski <kuba@kernel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Simon Horman <horms@kernel.org>
Cc: Stanislaw Gruszka <stf_xl@wp.pl>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
In alloc_hugetlb_folio(), a single h_cg pointer is used for both the rsvd
and non-rsvd hugetlb cgroup charges. When map_chg is set,
hugetlb_cgroup_charge_cgroup_rsvd() stores the charged cgroup in h_cg, but
the immediately following hugetlb_cgroup_charge_cgroup() overwrites h_cg
with the non-rsvd cgroup pointer.
As a result, hugetlb_cgroup_commit_charge_rsvd() stores the wrong
(non-rsvd) cgroup pointer into the folio's rsvd slot.
When the folio is later freed, free_huge_folio() unconditionally calls
both hugetlb_cgroup_uncharge_folio() and
hugetlb_cgroup_uncharge_folio_rsvd(). The rsvd uncharge reads back the
wrong cgroup from the folio and decrements a counter that was never
charged for that cgroup, causing a page_counter underflow:
page_counter underflow: -512 nr_pages=512
WARNING: mm/page_counter.c:61 at page_counter_cancel
Fix this by introducing a separate h_cg_rsvd pointer exclusively for the
rsvd charge path, keeping the rsvd and non-rsvd charges fully independent
through their charge, commit, and error uncharge paths.
Link: https://lore.kernel.org/20260328065534.346053-1-kartikey406@gmail.com
Fixes: 08cf9faf75 ("hugetlb_cgroup: support noreserve mappings")
Reported-by: syzbot+226c1f947186f8fef796@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=226c1f947186f8fef796
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Mina Almasry <almasrymina@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Of all observable lruvec lock contention in our fleet, we find that ~24%
occurs when dead folios are present in lru_add batches at drain time.
This is wasteful in the sense that the folio is added to the LRU just to
be immediately removed via folios_put_refs(), incurring two unnecessary
lock acquisitions.
Eliminate this overhead by preemptively cleaning up dead folios before
they make it into the LRU. Use folio_ref_freeze() to filter folios whose
only remaining refcount is the batch ref. When dead folios are found,
move them off the add batch and onto a temporary batch to be freed.
PG_active may be set on a batched folio as well as PG_unevictable (via
migration path). Since filtered folios bypass the normal lru_add()
cleanup, both flags must be cleared before freeing.
During A/B testing on one of our prod instagram workloads (high-frequency
short-lived requests), the patch intercepted almost all dead folios before
they entered the LRU. Data collected using the mm_lru_insertion
tracepoint shows the effectiveness of the patch:
Per-host LRU add averages at 95% CPU load
(60 hosts each side, 3 x 60s intervals)
dead folios/min total folios/min dead %
unpatched: 1,297,785 19,341,986 6.7097%
patched: 14 19,039,996 0.0001%
Within this workload, we save ~2.6M lock acquisitions per minute per host
as a result.
System-wide memory stats improved on the patched side also at 95% CPU load:
- direct reclaim scanning reduced 7%
- allocation stalls reduced 5.2%
- compaction stalls reduced 12.3%
- page frees reduced 4.9%
No regressions were observed in requests served per second or request tail
latency (p99). Both metrics showed directional improvement at higher CPU
utilization (comparing 85% to 95%).
Note that tests were performed using classic LRU.
Link: https://lore.kernel.org/20260425053417.351146-1-jp.kobryn@linux.dev
Signed-off-by: JP Kobryn (Meta) <jp.kobryn@linux.dev>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Previously, we had warnings when a single page allocation took longer than
reasonably expected. This was introduced in commit 63f53dea0c ("mm:
warn about allocations which stall for too long").
The warning was subsequently reverted in commit 400e22499d ("mm: don't
warn about allocations which stall for too long") because it was possible
to generate memory pressure that would effectively stall further progress
through printk execution.
Page allocation stalls in excess of 10 seconds are always useful to debug
because they can result in severe userspace unresponsiveness. Adding this
artifact can be used to correlate with userspace going out to lunch and to
understand the state of memory at the time.
There should be a reasonable expectation that this warning will never
trigger given it is very passive, it will only be emitted when a page
allocation takes longer than 10 seconds. If it does trigger, this reveals
an issue that should be fixed: a single page allocation should never loop
for more than 10 seconds without oom killing to make memory available.
Unlike the original implementation, this implementation only reports
stalls once for the system every 10 seconds. Otherwise, many concurrent
reclaimers could spam the kernel log unnecessarily. Stalls are only
reported when calling into direct reclaim.
Link: https://lore.kernel.org/371c86c8-1d47-bd70-b74c-769842718b1f@google.com
Signed-off-by: David Rientjes <rientjes@google.com>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Petr Mladek <pmladek@suse.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>
There is already an 'if TRANSPARENT_HUGEPAGE' condition wrapping several
config options e.g. 'READ_ONLY_THP_FOR_FS', making the 'depends on'
statement for each of these a duplicate dependency (dead code).
I propose leaving the outer 'if TRANSPARENT_HUGEPAGE...endif' and removing
the individual 'depends on TRANSPARENT_HUGEPAGE' statement from each
option.
This dead code was found by kconfirm, a static analysis tool for Kconfig.
Link: https://lore.kernel.org/20260331070730.33915-1-julianbraha@gmail.com
Signed-off-by: Julian Braha <julianbraha@gmail.com>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
These two variables are redundant, squash them to align
alloc_pages_bulk_noprof() with the style used in
alloc_frozen_pages_nolock_noprof().
Link: https://lore.kernel.org/20260331-b4-prepare_alloc_pages-flags-v1-1-ea2416def698@google.com
Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Vishal Moola <vishal.moola@gmail.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Replace the hardcoded magic number 3 in get_any_page() with the existing
GET_PAGE_MAX_RETRY_NUM macro for code consistency and maintainability.
This change has no functional impact, only improves code readability and
unifies the retry limit configuration.
Link: https://lore.kernel.org/20260402064946.1124250-1-18810879172@163.com
Signed-off-by: wangxuewen <wangxuewen@kylinos.cn>
Acked-by: SeongJae Park <sj@kernel.org>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
swap_iocb->pages tracks the number of bvec entries (folios), not base
pages. Rename the array from bvec to bvecs and the counter from pages to
nr_bvecs to accurately reflect their purpose.
Link: https://lore.kernel.org/20260402072650.48811-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: NeilBrown <neil@brown.name>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
When reclaim is triggered by high order allocations on a fragmented
system, vmpressure() can report poor reclaim efficiency even though the
system has plenty of free memory. This is because many pages are scanned,
but few are found to actually reclaim - the pages are actively in use and
don't need to be freed. The resulting scan:reclaim ratio causes
vmpressure() to assert socket pressure, throttling TCP throughput
unnecessarily.
Costly order allocations (above PAGE_ALLOC_COSTLY_ORDER) rely heavily on
compaction to succeed, so poor reclaim efficiency at these orders does not
necessarily indicate memory pressure. The kernel already treats this
order as the boundary where reclaim is no longer expected to succeed and
compaction may take over.
Make vmpressure() order-aware through an additional parameter sourced from
scan_control at existing call sites. Socket pressure is now only asserted
when order <= PAGE_ALLOC_COSTLY_ORDER.
Memcg reclaim is unaffected since try_to_free_mem_cgroup_pages() always
uses order 0, which passes the filter unconditionally. Similarly,
vmpressure_prio() now passes order 0 internally when calling vmpressure(),
ensuring critical pressure from low reclaim priority is not suppressed by
the order filter.
The patch was motivated by a case of impacted net throughput in
production. On one affected host, the memory state at the time showed
~15GB available, zero cgroup pressure, and the following buddyinfo state:
Order FreePages
0: 133,970
1: 29,230
2: 17,351
3: 18,984
7+: 0
Using bpf, it was found that 94% of vmpressure calls on this host were
from order-7 kswapd reclaim.
TCP minimum recv window is rcv_ssthresh:19712.
Before patch:
723 out of 3,843 (19%) TCP connections stuck at minimum recv window
After live-patching and ~30min elapsed:
0 out of 3,470 TCP connections stuck at minimum recv window
Link: https://lore.kernel.org/20260406195014.112521-1-jp.kobryn@linux.dev
Signed-off-by: JP Kobryn (Meta) <jp.kobryn@linux.dev>
Reviewed-by: Rik van Riel <riel@surriel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Barry Song <baohua@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <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 <qi.zheng@linux.dev>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Wei Xu <weixugc@google.com>
Cc: Yuanchu Xie <yuanchu@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Replace the hardcoded if/else chain of test_bit() calls and string
literals in defrag_show() with a loop over defrag_flags[] and
defrag_mode_strings[] arrays introduced in the previous commit.
This makes defrag_show() consistent with defrag_store() and eliminates the
duplicated mode name strings.
Link: https://lore.kernel.org/20260408-thp_defrag-v2-2-bc544c1bde4e@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm: huge_memory: clean up defrag sysfs with shared", v2.
Refactor defrag_store() and defrag_show() to use shared data tables
instead of duplicated if/else chains.
Patch 1 introduces an enum defrag_mode, a defrag_mode_strings[] table, and
a defrag_flags[] mapping array, then rewrites defrag_store() to use
sysfs_match_string() with a loop over defrag_flags[].
Patch 2 refactors defrag_show() to use the same arrays, replacing its
hardcoded if/else chain of test_bit() calls and string literals.
This follows the same pattern applied to anon_enabled_store() in commit
522dfb4ba71f ("mm: huge_memory: refactor anon_enabled_store() with
change_anon_orders()").
This patch (of 2):
Replace the if/else chain of sysfs_streq() calls in defrag_store() with
sysfs_match_string() and a defrag_mode_strings[] table.
Introduce enum defrag_mode and defrag_flags[] array mapping each mode to
its corresponding transparent_hugepage_flag. The store function now loops
over defrag_flags[], setting the bit for the selected mode and clearing
the others. When mode is DEFRAG_NEVER (index 4), no index in the
4-element defrag_flags[] matches, so all flags are cleared.
Note that the enum ordering (always, defer, defer+madvise, madvise, never)
differs from the original if/else chain order in defrag_store() (always,
defer+madvise, defer, madvise, never). This is intentional to match the
display order used by defrag_show().
This is a follow-up cleanup to commit 522dfb4ba71f ("mm: huge_memory:
refactor anon_enabled_store() with change_anon_orders()") which applied
the same sysfs_match_string() pattern to anon_enabled_store().
Link: https://lore.kernel.org/20260408-thp_defrag-v2-0-bc544c1bde4e@debian.org
Link: https://lore.kernel.org/20260408-thp_defrag-v2-1-bc544c1bde4e@debian.org
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Tested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Tested-by: Zi Yan <ziy@nvidia.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
PMD alignment in khugepaged is currently implemented using a mix of
rounding helpers and open-coded bitmask operations.
Use ALIGN() and ALIGN_DOWN() consistently for PMD-sized address range
alignment, matching the preferred style for address and size handling.
No functional change intended.
Link: https://lore.kernel.org/20260409014323.2385982-1-ye.liu@linux.dev
Signed-off-by: Ye Liu <liuye@kylinos.cn>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam@infradead.org>
Cc: Liu Ye <liuye@kylinos.cn>
Cc: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
'forcekill' is used as a boolean flag to control whether processes should
be forcibly killed. It is only assigned from boolean expressions and
never used in arithmetic or bitmask operations.
Convert it from int to bool.
No functional change intended.
Link: https://lore.kernel.org/20260410074740.2524718-1-ye.liu@linux.dev
Signed-off-by: Ye Liu <liuye@kylinos.cn>
Reviewed-by: SeongJae Park <sj@kernel.org>
Acked-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Liu Ye <liuye@kylinos.cn>
Cc: Naoya Horiguchi <nao.horiguchi@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Commit 9bdac91424 ("sparsemem: Put mem map for one node together.")
introduced a mechanism to pre-allocate a large memory block to hold all
memmaps for a NUMA node upfront.
However, the original commit message did not clearly state the actual
benefits or the necessity of explicitly pre-allocating a single chunk for
all memmap areas of a given node.
One of the concerns about removing this pre-allocation is that the
subsequent per-section memmap allocations could become scattered around,
and might turn too many memory blocks/sections into an "un-offlinable"
state. However, tests show that even without the explicit node-wide
pre-allocation, memblock still allocates memory closely and back-to-back.
When tracing vmemmap_set_pmd allocations, the physical chunks allocated by
memblock are strictly adjacent to each other in a single contiguous
physical range (mapped top-down). Because they are packed tightly
together naturally, they will at most consume or pollute the exact same
number of memory blocks as the explicit pre-allocation did.
Another concern is the boot performance impact of calling memmap_alloc()
multiple times compared to one large node-wide allocation. Tests on a
256GB VM showed that memmap allocation time increased from 199,555 ns to
741,292 ns. Even though it is 3.7x slower, on a 1TB machine, the entire
memory allocation time would only take a few milliseconds. This boot
performance difference is completely negligible.
Since no negative impact on memory offlining behavior or noticeable boot
performance regression was found, this patch proposes removing the
explicit node-wide memmap pre-allocation mechanism to reduce the
maintenance burden.
Link: https://lore.kernel.org/20260410092419.2446420-1-songmuchun@bytedance.com
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
DAMON is opted-in for DAMON patches scanning [1] and email delivery [2].
Clarify how that could be used on DAMON maintainer profile.
Link: https://lore.kernel.org/20260412211932.89038-1-sj@kernel.org
Link: https://github.com/sashiko-dev/sashiko/commit/ad9f4a98f958 [1]
Link: https://github.com/sashiko-dev/sashiko/commit/b554c7b6e733 [2]
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The %pGp format specifier expects an argument of type 'unsigned long *',
but page->flags is now of type 'memdesc_flags_t' (a struct containing an
unsigned long member 'f') after the introduction of memdesc_flags_t.
Fix the type mismatch by passing &page->flags.f instead of &page->flags,
which matches the expected type.
Link: https://lore.kernel.org/20260414075813.3425968-1-zhen.ni@easystack.cn
Fixes: 53fbef56e0 ("mm: introduce memdesc_flags_t")
Signed-off-by: Zhen Ni <zhen.ni@easystack.cn>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The test was not being run by the selftest framework so it was never
noticed that it would fail with an assertion failure on configs without
support for MAP_DROPPABLE. Update the test so that it is skipped instead
when MAP_DROPPABLE is not supported, and add it to the mmap category so
that the test is run by the framework.
Link: https://lore.kernel.org/20260416033939.49981-4-anthony.yznaga@oracle.com
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
For configs that support MAP_DROPPABLE verify that a mapping created with
MAP_DROPPABLE cannot be locked via mlock(), and that it will not be locked
if it's created after mlockall(MCL_FUTURE).
Link: https://lore.kernel.org/20260416033939.49981-3-anthony.yznaga@oracle.com
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "fix MAP_DROPPABLE not supported errno", v4.
Mark Brown reported seeing a regression in -next on 32 bit arm with the
mlock selftests. Before exiting and marking the tests failed, the
following message was logged after an attempt to create a MAP_DROPPABLE
mapping:
Bail out! mmap error: Unknown error 524
It turns out error 524 is ENOTSUPP which is an error that userspace is not
supposed to see, but it indicates in this instance that MAP_DROPPABLE is
not supported.
The first patch changes the errno returned to EOPNOTSUPP. The second
patch is a second version of a prior patch to introduce selftests to
verify locking behavior with droppable mappings with the additional change
to skip the tests when MAP_DROPPABLE is not supported. The third patch
fixes the MAP_DROPPABLE selftest so that it is run by the framework and
skips if MAP_DROPPABLE is not supported.
This patch (of 3):
On configs where MAP_DROPPABLE is not supported (currently any 32-bit
config except for PPC32), mmap fails with errno set to ENOTSUPP. However,
ENOTSUPP is not a standard error value that userspace knows about. The
acceptable userspace-visible errno to use is EOPNOTSUPP. checkpatch.pl
has a warning to this effect.
Link: https://lore.kernel.org/20260416033939.49981-1-anthony.yznaga@oracle.com
Link: https://lore.kernel.org/20260416033939.49981-2-anthony.yznaga@oracle.com
Fixes: 9651fcedf7 ("mm: add MAP_DROPPABLE for designating always lazily freeable mappings")
Signed-off-by: Anthony Yznaga <anthony.yznaga@oracle.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Reported-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Pedro Falcato <pfalcato@suse.de>
Reviewed-by: Lorenzo Stoakes (Oracle) <ljs@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jason A. Donenfeld <jason@zx2c4.com>
Cc: Liam Howlett <liam@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Fix three typos in comments:
- Line 112: "zome_reclaim_mode" -> "zone_reclaim_mode"
- Line 6208: "prioities" -> "priorities"
- Line 7067: "that that high" -> "that the high" (duplicated word)
Link: https://lore.kernel.org/20260416062302.727468-1-gxxa03070307@gmail.com
Signed-off-by: Xiang Gao <gaoxiang17@xiaomi.com>
Reviewed-by: Barry Song <baohua@kernel.org>
Reviewed-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Commit 850ed20539 ("mm: move array mem_section init code out of
memory_present()") moved mem_section allocation logic into
memblocks_present().
Before that move, memory_present() could be called multiple times, so
unlikely() matched the common case, where most calls found mem_section
already allocated.
After that move, memblocks_present() is called exactly once from
sparse_init(). Under CONFIG_SPARSEMEM_EXTREME, mem_section is always NULL
when it is called.
So remove unnecessary NULL check before allocating mem_section. No
functional change.
Link: https://lore.kernel.org/20260419144225.2875654-1-ekffu200098@gmail.com
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed by: Donet Tom <donettom@linux.ibm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Liam Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Remove the odd VM_WARN_ON_FOLIO(!folio, folio) usage and replace it with a
simpler VM_WARN_ON_ONCE(!folio) check.
Drop the redundant VM_WARN_ON_ONCE(!pmd_none(*pmdp) &&
!is_huge_zero_pmd(*pmdp)).
Refactor the PMD checks, making the control flow clearer and avoiding
duplicate condition checks.
Link: https://lore.kernel.org/20260419174747.10701-1-nueralspacetech@gmail.com
Signed-off-by: Sunny Patel <nueralspacetech@gmail.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Huang Ying <ying.huang@linux.alibaba.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Gregory Price <gourry@gourry.net>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
zswap writeback is asynchronous, but test_zswap.c checks writeback
counters immediately after reclaim/trigger paths. On some platforms (e.g.
ppc64le), this can race with background writeback and cause spurious
failures even when behavior is correct.
Add wait_for_writeback() to poll get_cg_wb_count() with a bounded
timeout, and use it in:
test_zswap_writeback_one() when writeback is expected
test_no_invasive_cgroup_shrink() for the wb_group check
This keeps the original before/after assertion style while making the
tests robust against writeback completion latency.
No test behavior change, selftest stability improvement only.
Link: https://lore.kernel.org/20260424040059.12940-9-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
In attempt_writeback(), a memsize of 4M only covers 64 pages on 64K page
size systems. When memory.reclaim is called, the kernel prefers
reclaiming clean file pages (binary, libc, linker, etc.) over swapping
anonymous pages. With only 64 pages of anonymous memory, the reclaim
target can be largely or entirely satisfied by dropping file pages,
resulting in very few or zero anonymous pages being pushed into zswap.
This causes zswap_usage to be extremely small or zero, making
zswap_usage/4 insufficient to create meaningful writeback pressure. The
test then fails because no writeback is triggered.
On 4K page size systems this is not an issue because 4M covers 1024
pages, and file pages are a small fraction of the reclaim target.
Fix this by:
- Always allocating 1024 pages regardless of page size. This ensures
enough anonymous pages to reliably populate zswap and trigger
writeback, while keeping the original 4M allocation on 4K systems.
- Setting zswap.max to zswap_usage/4 instead of zswap_usage/2 to
create stronger writeback pressure, ensuring reclaim reliably
triggers writeback even on large page size systems.
=== Error Log ===
# uname -rm
6.12.0-211.el10.ppc64le ppc64le
# getconf PAGESIZE
65536
# ./test_zswap
TAP version 13
1..7
ok 1 test_zswap_usage
ok 2 test_swapin_nozswap
ok 3 test_zswapin
not ok 4 test_zswap_writeback_enabled
...
Link: https://lore.kernel.org/20260424040059.12940-8-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Yosry Ahmed <yosry@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
test_no_invasive_cgroup_shrink sets up two cgroups: wb_group, which is
expected to trigger zswap writeback, and a control group (renamed to
zw_group), which should only have pages sitting in zswap without any
writeback.
There are two problems with the current test:
1) The data patterns are reversed. wb_group uses allocate_bytes(), which
writes only a single byte per page — trivially compressible,
especially by zstd — so compressed pages fit within zswap.max and
writeback is never triggered. Meanwhile, the control group uses
getrandom() to produce hard-to-compress data, but it is the group
that does *not* need writeback.
2) The test uses fixed sizes (10K zswap.max, 10MB allocation) that are
too small on systems with large PAGE_SIZE (e.g. 64K), failing to
build enough memory pressure to trigger writeback reliably.
Fix both issues by:
- Swapping the data patterns: fill wb_group pages with partially
random data (getrandom for page_size/4 bytes) to resist compression
and trigger writeback, and fill zw_group pages with simple repeated
data to stay compressed in zswap.
- Making all size parameters PAGE_SIZE-aware: set allocation size to
PAGE_SIZE * 1024, memory.zswap.max to PAGE_SIZE, and memory.max to
allocation_size / 2 for both cgroups.
- Allocating memory inline instead of via cg_run() so the pages
remain resident throughout the test.
=== Error Log ===
# getconf PAGESIZE
65536
# ./test_zswap
TAP version 13
...
ok 5 test_zswap_writeback_disabled
ok 6 # SKIP test_no_kmem_bypass
not ok 7 test_no_invasive_cgroup_shrink
Link: https://lore.kernel.org/20260424040059.12940-7-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
test_zswap uses hardcoded values of 4095 and 4096 throughout as page
stride and page size, which are only correct on systems with a 4K page
size. On architectures with larger pages (e.g., 64K on arm64 or ppc64),
these constants cause memory to be touched at sub-page granularity,
leading to inefficient access patterns and incorrect page count
calculations, which can cause test failures.
Replace all hardcoded 4095 and 4096 values with a global pagesize variable
initialized from sysconf(_SC_PAGESIZE) at startup, and remove the
redundant local sysconf() calls scattered across individual functions. No
functional change on 4K page size systems.
Link: https://lore.kernel.org/20260424040059.12940-6-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Yosry Ahmed <yosry@kernel.org>
Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
The cgroup utility code defines a local PAGE_SIZE macro hardcoded to 4096,
which is used primarily as a generic buffer size for reading cgroup and
proc files. This naming is misleading because the value has nothing to do
with the actual page size of the system. On architectures with larger
pages (e.g., 64K on arm64 or ppc64), the name suggests a relationship that
does not exist. Additionally, the name can shadow or conflict with
PAGE_SIZE definitions from system headers, leading to confusion or subtle
bugs.
To resolve this, rename the macro to BUF_SIZE to accurately reflect its
purpose as a general I/O buffer size.
Furthermore, test_memcontrol currently relies on this hardcoded 4K value
to stride through memory and trigger page faults. Update this logic to
use the actual system page size dynamically. This micro-optimizes the
memory faulting process by ensuring it iterates correctly and efficiently
based on the underlying architecture's true page size. (This part from
Waiman)
Link: https://lore.kernel.org/20260424040059.12940-5-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Yosry Ahmed <yosryahmed@google.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
test_zswapin compares memory.stat:zswpin (counted in pages) against a byte
threshold converted with PAGE_SIZE. In cgroup selftests, PAGE_SIZE is
hardcoded to 4096, which makes the conversion wrong on systems with non-4K
base pages (e.g. 64K).
As a result, the test requires too many pages to pass and fails spuriously
even when zswap is working.
Use sysconf(_SC_PAGESIZE) for the zswpin threshold conversion so the check
matches the actual system page size.
Link: https://lore.kernel.org/20260424040059.12940-4-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Reviewed-by: Yosry Ahmed <yosry@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "selftests/cgroup: improve zswap tests robustness and support
large page sizes", v7.
This patchset aims to fix various spurious failures and improve the
overall robustness of the cgroup zswap selftests.
The primary motivation is to make the tests compatible with architectures
that use non-4K page sizes (such as 64K on ppc64le and arm64). Currently,
the tests rely heavily on hardcoded 4K page sizes and fixed memory limits.
On 64K page size systems, these hardcoded values lead to sub-page
granularity accesses, incorrect page count calculations, and insufficient
memory pressure to trigger zswap writeback, ultimately causing the tests
to fail.
Additionally, this series addresses OOM kills occurring in
test_swapin_nozswap by dynamically scaling memory limits, and prevents
spurious test failures when zswap is built into the kernel but globally
disabled.
This patch (of 8):
test_zswap currently only checks whether zswap is present by testing
/sys/module/zswap. This misses the runtime global state exposed in
/sys/module/zswap/parameters/enabled.
When zswap is built/loaded but globally disabled, the zswap cgroup
selftests run in an invalid environment and may fail spuriously.
Check the runtime enabled state before running the tests:
- skip if zswap is not configured,
- fail if the enabled knob cannot be read,
- skip if zswap is globally disabled.
Also print a hint in the skip message on how to enable zswap.
Link: https://lore.kernel.org/20260424040059.12940-1-li.wang@linux.dev
Link: https://lore.kernel.org/20260424040059.12940-2-li.wang@linux.dev
Signed-off-by: Li Wang <li.wang@linux.dev>
Acked-by: Yosry Ahmed <yosry@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Tejun Heo <tj@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Jiayuan Chen <jiayuan.chen@linux.dev>
Cc: Waiman Long <longman@redhat.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Extend sysfs.py DAMON selftest to setup DAMOS action failed region quota
charge ratio and assert the setup is made into DAMON internal state.
Link: https://lore.kernel.org/20260428013402.115171-12-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Extend drgn_dump_damon_status.py to dump DAMON internal state for DAMOS
action failed regions quota charge ratio, to be able to show if the
internal state for the feature is working, with future DAMON selftests.
Link: https://lore.kernel.org/20260428013402.115171-11-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Extend _damon_sysfs.py for DAMOS action failed regions quota charge ratio
setup, so that we can add kselftest for the new feature.
Link: https://lore.kernel.org/20260428013402.115171-10-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Update DAMON ABI document for the DAMOS action failed regions quota charge
ratio control sysfs files.
Link: https://lore.kernel.org/20260428013402.115171-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Implement the user-space ABI for the DAMOS action failed region
quota-charge ratio setup. For this, add two new sysfs files under the
DAMON sysfs interface for DAMOS quotas. Names of the files are
fail_charge_num and fail_charge_denom, and work for reading and setting
the numerator and denominator of the failed regions charge ratio.
Link: https://lore.kernel.org/20260428013402.115171-5-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
DAMOS quota is charged to all DAMOS action application attempted memory,
regardless of how much of the memory the action was successful and failed.
This makes understanding quota behavior without DAMOS stat but only with
end level metrics (e.g., increased amount of free memory for DAMOS_PAGEOUT
action) difficult. Also, charging action-failed memory same as
action-successful memory is somewhat unfair, as successful action
application will induce more overhead in most cases.
Introduce DAMON core API for setting the charge ratio for such
action-failed memory. It allows API callers to specify the ratio in a
flexible way, by setting the numerator and the denominator.
Link: https://lore.kernel.org/20260428013402.115171-4-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
damos_apply_scheme() could split the given region if applying the scheme's
action to the entire region can result in violating the quota-set upper
limit. Keeping regions that are created by such split operations is
unnecessary overhead.
The overhead would be negligible in the common case because such split
operations could happen only up to the number of installed schemes per
scheme apply interval. The following commit could make the impact larger,
though. The following commit will allow the action-failed region to be
charged in a different ratio. If both the ratio and the remaining quota
is quite small while the region to apply the scheme is quite large and the
action is nearly always failing, a high number of split operations could
happen.
Remove the unnecessary overhead by merging regions after applying schemes
is done for each region. The merge operation is made only if it will not
lose monitoring information and keep min_nr_regions constraint. In the
worst case, the max_nr_regions could still be violated until the next
per-aggregation interval merge operation is made.
Link: https://lore.kernel.org/20260428013402.115171-3-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "mm/damon: introduce DAMOS failed region quota charge ratio".
Let users set different DAMOS quota charge ratios for DAMOS action failed
regions, for deterministic and consistent DAMOS action progress.
Common Reports: Unexpectedly Slow DAMOS
=======================================
One common issue report that we get from DAMON users is that DAMOS action
applying progress speed is sometimes much slower than expected. And one
common root cause is that the DAMOS quota is exceeded by the action
applying failed memory regions.
For example, a group of users tried to run DAMOS-based proactive memory
reclamation (DAMON_RECLAIM) with 100 MiB per second DAMOS quota. They ran
it on a system having no active workload which means all memory of the
system is cold. The expectation was that the system will show 100 MiB per
second reclamation until (nearly) all memory is reclaimed. But what they
found is that the speed is quite inconsistent and sometimes it becomes
very slower than the expectation, sometimes even no reclamation at all for
about tens of seconds. The upper limit of the speed (100 MiB per second)
was being kept as expected, though.
By monitoring the qt_exceeds (number of DAMOS quota exceed events) DAMOS
stat, we found DAMOS quota is always exceeded when the speed is slow. By
monitoring sz_tried and sz_applied (the total amount of DAMOS action tried
memory and succeeded memory) DAMOS stats together, we found the
reclamation attempts nearly always failed when the speed is slow.
DAMOS quota charges DAMOS action tried regions regardless of the
successfulness of the try. Hence in the example reported case, there was
unreclaimable memory spread around the system memory. Sometimes nearly
100 MiB of memory that DAMOS tried to reclaim in the given quota interval
was reclaimable, and therefore showed nearly 100 MiB per second speed.
Sometimes nearly 99 MiB of memory that DAMOS was trying to reclaim in the
given quota interval was unreclaimable, and therefore showing only about 1
MiB per second reclaim speed.
We explained it is an expected behavior of the feature rather than a bug,
as DAMOS quota is there for only the upper-limit of the speed. The users
agreed and later reported a huge win from the adoption of DAMON_RECLAIM on
their products.
It is Not a Bug but a Feature; But...
=====================================
So nothing is broken. DAMOS quota is working as intended, as the upper
limit of the speed. It also provides its behavior observability via DAMOS
stat. In the real world production environment that runs long term active
workloads and matters stability, the speed sometimes being slow is not a
real problem.
But, the non-deterministic behavior is sometimes annoying, especially in
lab environments. Even in a realistic production environment, when there
is a huge amount of DAMOS action unapplicable memory, the speed could be
problematically slow. Let's suppose a virtual machines provider that
setup 99% of the host memory as hugetlb pages that cannot be reclaimed, to
give it to virtual machines. Also, when aim-oriented DAMOS auto-tuning is
applied, this could also make the internal feedback loop confused.
The intention of the current behavior was that trying DAMOS action to
regions would anyway impose some overhead, and therefore somehow be
charged. But in the real world, the overhead for failed action is much
lighter than successful action. Charging those at the same ratio may be
unfair, or at least suboptimum in some environments.
DAMOS Action Failed Region Quota Charge Ratio
=============================================
Let users set the charge ratio for the action-failed memory, for more
optimal and deterministic use of DAMOS. It allows users to specify the
numerator and the denominator of the ratio for flexible setup. For
example, let's suppose the numerator and the denominator are set to 1 and
4,096, respectively. The ratio is 1 / 4,096. A DAMOS scheme action is
applied to 5 GiB memory. For 1 GiB of the memory, the action is
succeeded. For the rest (4 GiB), the action is failed. Then, only 1 GiB
and 1 MiB quota is charged.
The optimal charge ratio will depend on the use case and system/workload.
I'd recommend starting from setting the nominator as 1 and the denominator
as PAGE_SIZE and tune based on the results, because many DAMOS actions are
applied at page level.
Tests
=====
I tested this feature in the steps below.
1. Allocate 50% of system memory and mlock() it using a test program.
2. Fill up the page cache to exhaust nearly all free memory.
3. Start DAMON-based proactive reclamation with 100 MiB/second DAMOS
hard-quota. Auto-tune the DAMOS soft-quota under the hard-quota for
achieving 40% free memory of the system with 'temporal' tuner.
For step 1, I run a simple C program that is written by Gemini. It is
quite straightforward, so I'm not sharing the code here.
For step 2, I use dd command like below:
dd if=/dev/zero of=foo bs=1M count=$50_percent_of_system_memory
For step 3, I use the latest version of DAMON user-space tool (damo) like
below.
sudo damo start --damos_action pageout \
` # Do the pageout only up to 100 MiB per second ` \
--damos_quota_space 100M --damos_quota_interval 1s \
` # Auto-tune the quota below the hard quota aiming` \
` # 40% free memory of the node 0 ` \
` # (entire node of the test system)` \
--damos_quota_goal node_mem_free_bp 40% 0 \
` # use temporal tuner, which is easy to understnd ` \
--damos_quota_goal_tuner temporal
As expected, the progress of the reclamation is not consistent, because
the quota is exceeded for the failed reclamation of the unreclaimable
memory.
I do this again, but with the failed region charge ratio feature. For
this, the above 'damo' command is used, after appending command line
option for setup of the charge ratio like below. Note that the option was
added to 'damo' after v3.1.9.
sudo ./damo start --damos_action pageout \
[...]
` # quota-charge only 1/4096 for pageout-failed regions ` \
--damos_quota_fail_charge_ratio 1 4096
The progress of the reclamation was nearly 100 MiB per second until the
goal was achieved, meeting the expectation.
Patches Sequence
================
The first two patches make preparational changes. Patch 1 updates fully
charged quota check to handle <min_region_sz remaining quota, which will
be able to exist after this series is applied. Patch 2 merges regions
after applying schemes is done as long as it is ok to do, since regions
split operations for quota could happen much more frequently under a
corner case that this series will make available.
Patch 3 implements the feature and exposes it via DAMON core API. Patch 4
implements DAMON sysfs ABI for the feature. Three following patches (5-7)
document the feature and ABI on design, usage, and ABI documents,
respectively. Four patches for testing of the new feature follow. Patch
8 implements a kunit test for the feature. Patches 9 and 10 extend DAMON
selftest helpers for DAMON sysfs control and internal state dumping for
adding a new selftest for the feature. Patch 11 extends existing DAMON
sysfs interface selftest to test the new feature using the extended helper
scripts.
This patch (of 11):
Less than min_region_sz remaining quota effectively means the quota is
fully charged. In other words, no remaining quota. This is because DAMOS
actions are applied in the region granularity, and each region should have
min_region_sz or larger size. However the existing fully charged quota
check, which is also used for setting charge_target_from and
charge_addr_from of the quota, is not aware of the case. For the reason,
charge_target_from and charge_addr_from of the quota will not be updated
in the case. This can result in DAMOS action being applied more
frequently to a specific area of the memory.
The case is unreal because quota charging is also made in the region
granularity. It could be changed in future, though. Actually, the
following commit will make the change, by allowing users to set arbitrary
quota charging ratio for action-failed regions. To be prepared for the
change, update the fully charged quota checks to treat having less than
min_region_sz remaining quota as fully charged.
Link: https://lore.kernel.org/20260428013402.115171-1-sj@kernel.org
Link: https://lore.kernel.org/20260428013402.115171-2-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
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: Shuah Khan <shuah@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
