linux-kernel - Re: [PATCH v1 8/9] vmscan: memcg: sleep when flushing stats during reclaim

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Message-ID: <CALvZod7wJ-e-dHEhMynquiqQWFU2j+05wUyUe_yv_rBqJLu2rw@mail.gmail.com>
Date:   Tue, 28 Mar 2023 08:19:33 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Tejun Heo <tj@...nel.org>, Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Muchun Song <muchun.song@...ux.dev>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Koutný <mkoutny@...e.com>,
        Vasily Averin <vasily.averin@...ux.dev>,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH v1 8/9] vmscan: memcg: sleep when flushing stats during reclaim

On Mon, Mar 27, 2023 at 11:16 PM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> Memory reclaim is a sleepable context. Allow sleeping when flushing
> memcg stats to avoid unnecessarily performing a lot of work without
> sleeping. This can slow down reclaim code if flushing stats is taking
> too long, but there is already multiple cond_resched()'s in reclaim
> code.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

Acked-by: Shakeel Butt <shakeelb@...gle.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a9511ccb936f..9c1c5e8b24b8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -2845,7 +2845,7 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
>          * Flush the memory cgroup stats, so that we read accurate per-memcg
>          * lruvec stats for heuristics.
>          */
> -       mem_cgroup_flush_stats_atomic();
> +       mem_cgroup_flush_stats();

I wonder if we should just replace this with
mem_cgroup_flush_stats_ratelimited().