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From:   Shakeel Butt <shakeelb@google.com>
Date:   Tue, 28 Mar 2023 08:09:43 -0700
Message-ID: <CALvZod7ekQD-ygrv2M-QZzDFVTj7O-v7iCYOHKp3iqG6c-Rt1g@mail.gmail.com>
Subject: Re: [PATCH v1 6/9] memcg: sleep during flushing stats in safe contexts
To:     Yosry Ahmed <yosryahmed@google.com>
Cc:     Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
        Jens Axboe <axboe@kernel.dk>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>,
        Andrew Morton <akpm@linux-foundation.org>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Vasily Averin <vasily.averin@linux.dev>,
        cgroups@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        bpf@vger.kernel.org
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On Mon, Mar 27, 2023 at 11:16=E2=80=AFPM Yosry Ahmed <yosryahmed@google.com=
> wrote:
>
> Currently, all contexts that flush memcg stats do so with sleeping not
> allowed. Some of these contexts are perfectly safe to sleep in, such as
> reading cgroup files from userspace or the background periodic flusher.
>
> Refactor the code to make mem_cgroup_flush_stats() non-atomic (aka
> sleepable), and provide a separate atomic version. The atomic version is
> used in reclaim, refault, writeback, and in mem_cgroup_usage(). All
> other code paths are left to use the non-atomic version. This includes
> callbacks for userspace reads and the periodic flusher.
>
> Since refault is the only caller of mem_cgroup_flush_stats_ratelimited(),
> this function is changed to call the atomic version of
> mem_cgroup_flush_stats(). Reclaim and refault code paths are modified
> to do non-atomic flushing in separate later patches -- so
> mem_cgroup_flush_stats_ratelimited() will eventually become non-atomic.
>
> Signed-off-by: Yosry Ahmed <yosryahmed@google.com>

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