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ipc/shm: fix RSS accounting for hugetlb shared memory

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Commit a08c7193e4 ("mm/filemap: remove hugetlb special casing in
filemap.c") changed mapping->nrpages to count base pages for hugetlb
folios.  However, shm_add_rss_swap() still multiplies it by
pages_per_huge_page(), overcounting RSS in both SHM_INFO and
/proc/sysvipc/shm.

Use mapping->nrpages for RSS accounting across all backing types, and
account swap only for non-hugetlb shmem.  Use READ_ONCE() for both
counters instead of info->lock, which does not protect nrpages and cannot
provide a consistent snapshot.

Link: https://lore.kernel.org/20261014082218.2236088-1-tongweilin@linux.alibaba.com
Fixes: a08c7193e4 ("mm/filemap: remove hugetlb special casing in filemap.c")
Signed-off-by: Weilin Tong <tongweilin@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested-by: Muchun Song <muchun.song@linux.dev>
Acked-by: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: David Hildenbrand <david@kernel.org>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
This commit is contained in:
Weilin Tong 2026-10-14 16:22:18 +08:00 committed by Andrew Morton
parent 00a51d0991
commit e387ebe5cd
1 changed files with 4 additions and 19 deletions
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23
ipc/shm.c
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@ -936,26 +936,11 @@ static inline unsigned long copy_shminfo_to_user(void __user *buf, struct shminf
static void shm_add_rss_swap(struct shmid_kernel *shp,
unsigned long *rss_add, unsigned long *swp_add)
{
struct inode *inode;
struct inode *inode = file_inode(shp->shm_file);
inode = file_inode(shp->shm_file);
if (is_file_hugepages(shp->shm_file)) {
struct address_space *mapping = inode->i_mapping;
struct hstate *h = hstate_file(shp->shm_file);
*rss_add += pages_per_huge_page(h) * mapping->nrpages;
} else {
#ifdef CONFIG_SHMEM
struct shmem_inode_info *info = SHMEM_I(inode);
spin_lock_irq(&info->lock);
*rss_add += inode->i_mapping->nrpages;
*swp_add += info->swapped;
spin_unlock_irq(&info->lock);
#else
*rss_add += inode->i_mapping->nrpages;
#endif
}
*rss_add += READ_ONCE(inode->i_mapping->nrpages);
if (IS_ENABLED(CONFIG_SHMEM) && !is_file_hugepages(shp->shm_file))
*swp_add += READ_ONCE(SHMEM_I(inode)->swapped);
}
/*