Commit dad2dc9c authored by Hugh Dickins's avatar Hugh Dickins Committed by Andrew Morton
Browse files

mm: shmem: fix ShmemHugePages at swapout 

/proc/meminfo ShmemHugePages has been showing overlarge amounts (more than
Shmem) after swapping out THPs: we forgot to update NR_SHMEM_THPS.

Add shmem_update_stats(), to avoid repetition, and risk of making that
mistake again: the call from shmem_delete_from_page_cache() is the bugfix;
the call from shmem_replace_folio() is reassuring, but not really a bugfix
(replace corrects misplaced swapin readahead, but huge swapin readahead
would be a mistake).

Link: https://lkml.kernel.org/r/5ba477c8-a569-70b5-923e-09ab221af45b@google.com


Fixes: 809bc865 ("mm: shmem: support large folio swap out")
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Reviewed-by: default avatarShakeel Butt <shakeel.butt@linux.dev>
Reviewed-by: default avatarYosry Ahmed <yosryahmed@google.com>
Reviewed-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Tested-by: default avatarBaolin Wang <baolin.wang@linux.alibaba.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7782e3b3

mm/shmem.c

+12 −10
Original line number Diff line number Diff line
@@ -787,6 +787,14 @@ static bool shmem_huge_global_enabled(struct inode *inode, pgoff_t index, 
}

#endif /* CONFIG_TRANSPARENT_HUGEPAGE */



static void shmem_update_stats(struct folio *folio, int nr_pages)

{

	if (folio_test_pmd_mappable(folio))

		__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, nr_pages);

	__lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr_pages);

	__lruvec_stat_mod_folio(folio, NR_SHMEM, nr_pages);

}



/*

 * Somewhat like filemap_add_folio, but error if expected item has gone.

 */
@@ -821,10 +829,7 @@ static int shmem_add_to_page_cache(struct folio *folio, 
		xas_store(&xas, folio);

		if (xas_error(&xas))

			goto unlock;

		if (folio_test_pmd_mappable(folio))

			__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, nr);

		__lruvec_stat_mod_folio(folio, NR_FILE_PAGES, nr);

		__lruvec_stat_mod_folio(folio, NR_SHMEM, nr);

		shmem_update_stats(folio, nr);

		mapping->nrpages += nr;

unlock:

		xas_unlock_irq(&xas);
@@ -852,8 +857,7 @@ static void shmem_delete_from_page_cache(struct folio *folio, void *radswap) 
	error = shmem_replace_entry(mapping, folio->index, folio, radswap);

	folio->mapping = NULL;

	mapping->nrpages -= nr;

	__lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);

	__lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);

	shmem_update_stats(folio, -nr);

	xa_unlock_irq(&mapping->i_pages);

	folio_put_refs(folio, nr);

	BUG_ON(error);
@@ -1969,10 +1973,8 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp, 
	}

	if (!error) {

		mem_cgroup_replace_folio(old, new);

		__lruvec_stat_mod_folio(new, NR_FILE_PAGES, nr_pages);

		__lruvec_stat_mod_folio(new, NR_SHMEM, nr_pages);

		__lruvec_stat_mod_folio(old, NR_FILE_PAGES, -nr_pages);

		__lruvec_stat_mod_folio(old, NR_SHMEM, -nr_pages);

		shmem_update_stats(new, nr_pages);

		shmem_update_stats(old, -nr_pages);

	}

	xa_unlock_irq(&swap_mapping->i_pages);