mm: do not update memcg stats for NR_{FILE/SHMEM}_PMDMAPPED

Previously, all NR_VM_EVENT_ITEMS stats were maintained per-memcg,
although some of those fields are not exposed anywhere. Commit
14e0f6c957e39 ("memcg: reduce memory for the lruvec and memcg stats")
changed this such that we only maintain the stats we actually expose
per-memcg via a translation table.

Additionally, commit 514462bbe927b ("memcg: warn for unexpected events
and stats") added a warning if a per-memcg stat update is attempted for
a stat that is not in the translation table. The warning started firing
for the NR_{FILE/SHMEM}_PMDMAPPED stat updates in the rmap code. These
stats are not maintained per-memcg, and hence are not in the translation
table.

Do not use __lruvec_stat_mod_folio() when updating NR_FILE_PMDMAPPED and
NR_SHMEM_PMDMAPPED. Use __mod_node_page_state() instead, which updates
the global per-node stats only.

Link: https://lkml.kernel.org/r/20240506192924.271999-1-yosryahmed@google.com
Fixes: 514462bbe927 ("memcg: warn for unexpected events and stats")
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Reported-by: syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/0000000000001b9d500617c8b23c@google.com
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index fd021efe02a1285ce249707a8cae60a3f3efe982..e8fc5ecb59b2f5ecdd9144786a17afd442273df9 100644 (file)
--- 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);
        }
        if (nr) {
                idx = folio_test_anon(folio) ? NR_ANON_MAPPED : NR_FILE_MAPPED;