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Tue, 04 Apr 2023 08:09:26 -0700 (PDT) Date: Tue, 4 Apr 2023 11:09:24 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Tejun Heo , Josef Bacik , Jens Axboe , Zefan Li , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Michal =?iso-8859-1?Q?Koutn=FD?= , Vasily Averin , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, Michal Hocko Subject: Re: [PATCH v3 5/8] memcg: sleep during flushing stats in safe contexts Message-ID: <20230404150924.GA11156@cmpxchg.org> References: <20230330191801.1967435-1-yosryahmed@google.com> <20230330191801.1967435-6-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230330191801.1967435-6-yosryahmed@google.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6B0552001E X-Stat-Signature: 781rt8cj458qij9m4qym8e6md7dq6drz X-Rspam-User: X-HE-Tag: 1680620967-84071 X-HE-Meta: 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 h6sSMewB 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Mar 30, 2023 at 07:17:58PM +0000, Yosry Ahmed 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. > Flushing is an expensive operation that scales with the number of cpus > and the number of cgroups in the system, so avoid doing it atomically > where possible. > > 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(), > change it to mem_cgroup_flush_stats_atomic_ratelimited(). Reclaim and > refault code paths are modified to do non-atomic flushing in separate > later patches -- so it will eventually be changed back to > mem_cgroup_flush_stats_ratelimited(). > > Signed-off-by: Yosry Ahmed > Acked-by: Shakeel Butt > Acked-by: Michal Hocko Acked-by: Johannes Weiner