Re: [PATCH] memcg: cleanup racy sum avoidance code

David Hildenbrand
2021-07-28T08:21:18Z

On 28.07.21 03:22, Shakeel Butt wrote:
> We used to have per-cpu memcg and lruvec stats and the readers have to
> traverse and sum the stats from each cpu. This summing was racy and may
> expose transient negative values. So, an explicit check was added to
> avoid such scenarios. Now these stats are moved to rstat infrastructure
> and are no more per-cpu, so we can remove the fixup for transient
> negative values.
>
> Signed-off-by: Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> ---
> include/linux/memcontrol.h | 15 ++-------------
> 1 file changed, 2 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 7028d8e4a3d7..5f2a39a43d47 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -991,30 +991,19 @@ static inline void mod_memcg_state(struct mem_cgroup *memcg,
>
> static inline unsigned long memcg_page_state(struct mem_cgroup *memcg, int idx)
> {
> - long x = READ_ONCE(memcg->vmstats.state[idx]);
> -#ifdef CONFIG_SMP
> - if (x < 0)
> - x = 0;
> -#endif
> - return x;
> + return READ_ONCE(memcg->vmstats.state[idx]);
> }
>
> static inline unsigned long lruvec_page_state(struct lruvec *lruvec,
> enum node_stat_item idx)
> {
> struct mem_cgroup_per_node *pn;
> - long x;
>
> if (mem_cgroup_disabled())
> return node_page_state(lruvec_pgdat(lruvec), idx);
>
> pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec);
> - x = READ_ONCE(pn->lruvec_stats.state[idx]);
> -#ifdef CONFIG_SMP
> - if (x < 0)
> - x = 0;
> -#endif
> - return x;
> + return READ_ONCE(pn->lruvec_stats.state[idx]);
> }
>
> static inline unsigned long lruvec_page_state_local(struct lruvec *lruvec,
>

Reviewed-by: David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>

--
Thanks,

David / dhildenb