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Thu, 30 Mar 2023 12:30:18 -0700 (PDT) Received: from localhost ([107.116.82.97]) by smtp.gmail.com with ESMTPSA id 2-20020a4a0302000000b005251f71250dsm13103ooi.37.2023.03.30.12.30.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 30 Mar 2023 12:30:17 -0700 (PDT) Date: Thu, 30 Mar 2023 15:30:13 -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: 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-Stat-Signature: kj5cptux8neu18bpyhs5gqjrj71dew74 X-Rspam-User: X-Rspamd-Queue-Id: 55B3C4000B X-Rspamd-Server: rspam06 X-HE-Tag: 1680204619-760494 X-HE-Meta: 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 aEAADKld 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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