Re: [PATCH] mm/memcg: Fix incorrect flushing of lruvec data in obj_stock
flat view
From: Michal Hocko <hidden>
Date: 2021-08-02 06:28:24
Also in:
linux-mm, lkml
On Sun 01-08-21 22:28:27, 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 hence the wrong node, not the one cached in obj_stock.
It would be great to explicitly mention user observable problems here. I do assume this will make slab stats skewed but the effect wouldn't be very big, right?
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 <redacted>Acked-by: Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org>
quoted hunk ↗ jump to hunk
--- mm/memcontrol.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ae1f5d0cb581..881ec4ddddcd 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -3106,17 +3106,19 @@ 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; + + stock->cached_pgdat = 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; } - stock->cached_pgdat = pgdat;
Minor nit. Is there any reason to move the cached_pgdat? TBH I found the original way better from the readability POV.
} bytes = (idx == NR_SLAB_RECLAIMABLE_B) ? &stock->nr_slab_reclaimable_b -- 2.18.1
-- Michal Hocko SUSE Labs