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 <longman@xxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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
