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Mercier" Date: Wed, 16 Oct 2024 10:17:22 -0700 Message-ID: Subject: Re: [PATCH v2] memcg: add tracing for memcg stat updates To: Shakeel Butt Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Steven Rostedt , JP Kobryn , Yosry Ahmed , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team , Michal Hocko , Muchun Song Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E054214000A X-Stat-Signature: iqfxkf77as58z9q8t1g95zo1icyfi1wq X-Rspam-User: X-HE-Tag: 1729099050-302806 X-HE-Meta: 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 tFOmhr+U 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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: List-Subscribe: List-Unsubscribe: On Tue, Oct 15, 2024 at 2:37=E2=80=AFPM Shakeel Butt wrote: > > The memcg stats are maintained in rstat infrastructure which provides ver= y > fast updates side and reasonable read side. However memcg added plethora > of stats and made the read side, which is cgroup rstat flush, very slow. > To solve that, threshold was added in the memcg stats read side i.e. no > need to flush the stats if updates are within the threshold. > > This threshold based improvement worked for sometime but more stats were > added to memcg and also the read codepath was getting triggered in the > performance sensitive paths which made threshold based ratelimiting > ineffective. We need more visibility into the hot and cold stats i.e. > stats with a lot of updates. Let's add trace to get that visibility. > > Signed-off-by: Shakeel Butt > Acked-by: Roman Gushchin > Reviewed-by: Yosry Ahmed > Cc: Michal Hocko > Cc: Johannes Weiner > Cc: Muchun Song > Cc: JP Kobryn > Cc: Steven Rostedt (Google) > Cc: Andrew Morton Reviewed-by: T.J. Mercier