[PATCH v2] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock

[PATCH v2] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock

[Waiman Long]

When mod_objcg_state() is called with a pgdat that is different from
that in the obj_stock, the old lruvec data cached in obj_stock are
flushed out. Unfortunately, they were flushed to the new pgdat and
so the data go to the wrong node. This will screw up the slab data
reported in /sys/devices/system/node/node*/meminfo.

Fix that by flushing the data to the cached pgdat instead.

Fixes: 68ac5b3c8db2 ("mm/memcg: cache vmstat data in percpu memcg_stock_pcp")
Signed-off-by: Waiman Long <longman@redhat.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
 mm/memcontrol.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index ae1f5d0cb581..87c883227f90 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3106,13 +3106,15 @@ void mod_objcg_state(struct obj_cgroup *objcg, struct pglist_data *pgdat,
 		stock->cached_pgdat = pgdat;
 	} else if (stock->cached_pgdat != pgdat) {
 		/* Flush the existing cached vmstat data */
+		struct pglist_data *oldpg = stock->cached_pgdat;
+
 		if (stock->nr_slab_reclaimable_b) {
-			mod_objcg_mlstate(objcg, pgdat, NR_SLAB_RECLAIMABLE_B,
+			mod_objcg_mlstate(objcg, oldpg, NR_SLAB_RECLAIMABLE_B,
 					  stock->nr_slab_reclaimable_b);
 			stock->nr_slab_reclaimable_b = 0;
 		}
 		if (stock->nr_slab_unreclaimable_b) {
-			mod_objcg_mlstate(objcg, pgdat, NR_SLAB_UNRECLAIMABLE_B,
+			mod_objcg_mlstate(objcg, oldpg, NR_SLAB_UNRECLAIMABLE_B,
 					  stock->nr_slab_unreclaimable_b);
 			stock->nr_slab_unreclaimable_b = 0;
 		}
-- 
2.18.1

Re: [PATCH v2] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock

[Shakeel Butt]

On Mon, Aug 2, 2021 at 7:38 AM Waiman Long <longman@redhat.com> wrote:
>
> When mod_objcg_state() is called with a pgdat that is different from
> that in the obj_stock, the old lruvec data cached in obj_stock are
> flushed out. Unfortunately, they were flushed to the new pgdat and
> so the data go to the wrong node. This will screw up the slab data
> reported in /sys/devices/system/node/node*/meminfo.
>
> Fix that by flushing the data to the cached pgdat instead.
>
> Fixes: 68ac5b3c8db2 ("mm/memcg: cache vmstat data in percpu memcg_stock_pcp")
> Signed-off-by: Waiman Long <longman@redhat.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Reviewed-by: Shakeel Butt <shakeelb@google.com>

Re: [PATCH v2] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock

[Roman Gushchin]

On Mon, Aug 02, 2021 at 10:38:34AM -0400, Waiman Long wrote:
> When mod_objcg_state() is called with a pgdat that is different from
> that in the obj_stock, the old lruvec data cached in obj_stock are
> flushed out. Unfortunately, they were flushed to the new pgdat and
> so the data go to the wrong node. This will screw up the slab data
> reported in /sys/devices/system/node/node*/meminfo.
> 
> Fix that by flushing the data to the cached pgdat instead.
> 
> Fixes: 68ac5b3c8db2 ("mm/memcg: cache vmstat data in percpu memcg_stock_pcp")
> Signed-off-by: Waiman Long <longman@redhat.com>
> Acked-by: Michal Hocko <mhocko@suse.com>

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!