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mm: fs: remove filemap_nr_thps*() functions and their users

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They are used by READ_ONLY_THP_FOR_FS to handle writes to FSes without
large folio support, so that read-only THPs created in these FSes are not
seen by the FSes when the underlying fd becomes writable.  Now read-only
PMD THPs only appear in a FS with large folio support and the supported
orders include PMD_ORDER.

READ_ONLY_THP_FOR_FS was using mapping->nr_thps, inode->i_writecount, and
smp_mb() to prevent writes to a read-only THP and collapsing writable
folios into a THP.  In collapse_file(), mapping->nr_thps is increased,
then smp_mb(), and if inode->i_writecount > 0, collapse is stopped, while
do_dentry_open() first increases inode->i_writecount, then a full memory
fence, and if mapping->nr_thps > 0, all read-only THPs are truncated.

Now this mechanism can be removed along with READ_ONLY_THP_FOR_FS code,
since a dirty folio check has been added after try_to_unmap() in
collapse_file() to prevent dirty folios from being collapsed as clean.

Link: https://lore.kernel.org/20260517135416.1434539-7-ziy@nvidia.com
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Mason <clm@fb.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Sterba <dsterba@suse.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Jan Kara <jack@suse.cz>
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: Nico Pache <npache@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Zi Yan 2026-05-17 09:54:08 -04:00 committed by Andrew Morton
parent e4df0f37bd
commit 044925f9b5
5 changed files with 0 additions and 86 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

27
fs/open.c
View File

@ -968,33 +968,6 @@ static int do_dentry_open(struct file *f,
if ((f->f_flags & O_DIRECT) && !(f->f_mode & FMODE_CAN_ODIRECT))
return -EINVAL;
/*
* XXX: Huge page cache doesn't support writing yet. Drop all page
* cache for this file before processing writes.
*/
if (f->f_mode & FMODE_WRITE) {
/*
* Depends on full fence from get_write_access() to synchronize
* against collapse_file() regarding i_writecount and nr_thps
* updates. Ensures subsequent insertion of THPs into the page
* cache will fail.
*/
if (filemap_nr_thps(inode->i_mapping)) {
struct address_space *mapping = inode->i_mapping;
filemap_invalidate_lock(inode->i_mapping);
/*
* unmap_mapping_range just need to be called once
* here, because the private pages is not need to be
* unmapped mapping (e.g. data segment of dynamic
* shared libraries here).
*/
unmap_mapping_range(mapping, 0, 0, 0);
truncate_inode_pages(mapping, 0);
filemap_invalidate_unlock(inode->i_mapping);
}
}
return 0;
cleanup_all:

29
include/linux/pagemap.h
View File

@ -546,35 +546,6 @@ static inline size_t mapping_max_folio_size(const struct address_space *mapping)
return PAGE_SIZE << mapping_max_folio_order(mapping);
}
static inline int filemap_nr_thps(const struct address_space *mapping)
{
#ifdef CONFIG_READ_ONLY_THP_FOR_FS
return atomic_read(&mapping->nr_thps);
#else
return 0;
#endif
}
static inline void filemap_nr_thps_inc(struct address_space *mapping)
{
#ifdef CONFIG_READ_ONLY_THP_FOR_FS
if (!mapping_large_folio_support(mapping))
atomic_inc(&mapping->nr_thps);
#else
WARN_ON_ONCE(mapping_large_folio_support(mapping) == 0);
#endif
}
static inline void filemap_nr_thps_dec(struct address_space *mapping)
{
#ifdef CONFIG_READ_ONLY_THP_FOR_FS
if (!mapping_large_folio_support(mapping))
atomic_dec(&mapping->nr_thps);
#else
WARN_ON_ONCE(mapping_large_folio_support(mapping) == 0);
#endif
}
struct address_space *folio_mapping(const struct folio *folio);
/**

1
mm/filemap.c
View File

@ -189,7 +189,6 @@ static void filemap_unaccount_folio(struct address_space *mapping,
lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
} else if (folio_test_pmd_mappable(folio)) {
lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
filemap_nr_thps_dec(mapping);
}
if (test_bit(AS_KERNEL_FILE, &folio->mapping->flags))
mod_node_page_state(folio_pgdat(folio),

1
mm/huge_memory.c
View File

@ -3877,7 +3877,6 @@ static int __folio_freeze_and_split_unmapped(struct folio *folio, unsigned int n
} else {
lruvec_stat_mod_folio(folio,
NR_FILE_THPS, -nr);
filemap_nr_thps_dec(mapping);
}
}
}

28
mm/khugepaged.c
View File

@ -2480,21 +2480,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
goto xa_unlocked;
}
if (!is_shmem) {
filemap_nr_thps_inc(mapping);
/*
* Paired with the fence in do_dentry_open() -> get_write_access()
* to ensure i_writecount is up to date and the update to nr_thps
* is visible. Ensures the page cache will be truncated if the
* file is opened writable.
*/
smp_mb();
if (inode_is_open_for_write(mapping->host)) {
result = SCAN_FAIL;
filemap_nr_thps_dec(mapping);
}
}
xa_locked:
xas_unlock_irq(&xas);
xa_unlocked:
@ -2672,19 +2657,6 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
folio_putback_lru(folio);
folio_put(folio);
}
/*
* Undo the updates of filemap_nr_thps_inc for non-SHMEM
* file only. This undo is not needed unless failure is
* due to SCAN_COPY_MC.
*/
if (!is_shmem && result == SCAN_COPY_MC) {
filemap_nr_thps_dec(mapping);
/*
* Paired with the fence in do_dentry_open() -> get_write_access()
* to ensure the update to nr_thps is visible.
*/
smp_mb();
}
new_folio->mapping = NULL;