Re: [PATCH] mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED

From: Shakeel Butt
Date: Mon May 06 2024 - 15:25:40 EST


On Mon, May 06, 2024 at 05:00:24PM +0000, Yosry Ahmed wrote:
> Do not use __lruvec_stat_mod_folio() when updating NR_FILE_PMDMAPPED and
> NR_SHMEM_PMDMAPPED as these stats are not maintained per-memcg. Use
> __mod_node_page_state() instead, which updates the global per-node stats
> only.
>
> Reported-by: syzbot+9319a4268a640e26b72b@xxxxxxxxxxxxxxxxxxxxxxxxx
> Closes: https://lore.kernel.org/lkml/0000000000001b9d500617c8b23c@xxxxxxxxxx
> Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>

I think we can put Fixes either for 443c077dc2ec ("memcg: cleanup
__mod_memcg_lruvec_state") or ad86c0f0e089 ("memcg: warn for unexpected
events and stats").

> ---
> mm/rmap.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 12be4241474ab..c2cfb750d2535 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1435,13 +1435,14 @@ static __always_inline void __folio_add_file_rmap(struct folio *folio,
> struct page *page, int nr_pages, struct vm_area_struct *vma,
> enum rmap_level level)
> {
> + pg_data_t *pgdat = folio_pgdat(folio);
> int nr, nr_pmdmapped = 0;
>
> VM_WARN_ON_FOLIO(folio_test_anon(folio), folio);
>
> nr = __folio_add_rmap(folio, page, nr_pages, level, &nr_pmdmapped);
> if (nr_pmdmapped)
> - __lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
> + __mod_node_page_state(pgdat, folio_test_swapbacked(folio) ?
> NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
> if (nr)
> __lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr);
> @@ -1493,6 +1494,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
> enum rmap_level level)
> {
> atomic_t *mapped = &folio->_nr_pages_mapped;
> + pg_data_t *pgdat = folio_pgdat(folio);
> int last, nr = 0, nr_pmdmapped = 0;
> bool partially_mapped = false;
> enum node_stat_item idx;
> @@ -1540,13 +1542,14 @@ static __always_inline void __folio_remove_rmap(struct folio *folio,
> }
>
> if (nr_pmdmapped) {
> + /* NR_{FILE/SHMEM}_PMDMAPPED are not maintained per-memcg */
> if (folio_test_anon(folio))
> - idx = NR_ANON_THPS;
> - else if (folio_test_swapbacked(folio))
> - idx = NR_SHMEM_PMDMAPPED;
> + __lruvec_stat_mod_folio(folio, NR_ANON_THPS, -nr_pmdmapped);
> else
> - idx = NR_FILE_PMDMAPPED;
> - __lruvec_stat_mod_folio(folio, idx, -nr_pmdmapped);
> + __mod_node_page_state(pgdat,
> + folio_test_swapbacked(folio) ?
> + NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED,
> + nr_pmdmapped);

After the above fixed, you can add:

Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>