[Devel] [PATCH RHEL9 COMMIT] mm/memcontrol: fix non functioning swapin/out stats

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-427.77.1.vz9.86.x-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh9-5.14.0-427.77.1.vz9.86.5
------>
commit 3295297e295a218f2ea90c881a1365f6cee1c287
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Fri Aug 15 16:57:15 2025 +0800

    mm/memcontrol: fix non functioning swapin/out stats
    
    We count PSWPIN/OUT events via this code path:
    
      +-> count_memcg_page_event(folio, PSWPIN)
        +-> count_memcg_events(PSWPIN)
          +-> __count_memcg_events(PSWPIN)
            +-> index = memcg_events_index(idx=PSWPIN)
              +-> return mem_cgroup_events_index[idx] - 1
            +-> if (index >= 0)
              +-> __this_cpu_add(memcg->vmstats_percpu->events[i], count)
    
    And before that patch mem_cgroup_events_index[PSWPIN/OUT] was 0, which
    is "BAD" and leads to doing nothing.
    
    Fix that by adding PSWPIN/OUT to memcg_vm_event_stat.
    
    One more benefit from this change is that those stats are now also
    available in cgroup-v2 memory.stat file. Note though, that cgroup-v2
    event stats are printed via memcg_events and cgroup-v1 event stats are
    printed via memcg_events_local, so in v2 we have total sum of stats in
    all cgroup subdirectories, not just one cgroup.
    
    Fixes: 775cb9c41e708 ("mm: memcontrol: add swapin/out stats")
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    Feature: mm: statistic enhancements
---
 mm/memcontrol.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index cefb72234fda5..1b55b6d02d372 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -736,6 +736,8 @@ static const unsigned int memcg_vm_event_stat[] = {
 	THP_FAULT_ALLOC,
 	THP_COLLAPSE_ALLOC,
 #endif
+	PSWPIN,
+	PSWPOUT,
 };
 
 #define NR_MEMCG_EVENTS ARRAY_SIZE(memcg_vm_event_stat)