linux-kernel - Re: [PATCH v1 3/9] memcg: do not flush stats in irq context

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Message-ID: <ZCMnS8LWXQ4I6vYD@cmpxchg.org>
Date:   Tue, 28 Mar 2023 13:43:39 -0400
From:   Johannes Weiner <hannes@...xchg.org>
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>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Shakeel Butt <shakeelb@...gle.com>,
        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 3/9] memcg: do not flush stats in irq context

On Tue, Mar 28, 2023 at 06:16:32AM +0000, Yosry Ahmed wrote:
> Currently, the only context in which we can invoke an rstat flush from
> irq context is through mem_cgroup_usage() on the root memcg when called
> from memcg_check_events(). An rstat flush is an expensive operation that
> should not be done in irq context, so do not flush stats and use the
> stale stats in this case.
> 
> Arguably, usage threshold events are not reliable on the root memcg
> anyway since its usage is ill-defined.
> 
> Suggested-by: Johannes Weiner <hannes@...xchg.org>
> Suggested-by: Shakeel Butt <shakeelb@...gle.com>
> Signed-off-by: Yosry Ahmed <yosryahmed@...gle.com>

Excellent, thanks!

Acked-by: Johannes Weiner <hannes@...xchg.org>