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From: Shakeel Butt To: Roman Gushchin Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Muchun Song , Steven Rostedt , JP Kobryn , Yosry Ahmed , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team Subject: Re: [PATCH] memcg: add tracing for memcg stat updates Message-ID: References: <20241010003550.3695245-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: A8238180008 X-Rspamd-Server: rspam01 X-Stat-Signature: 9pwtdoqzbry644ctu6nqjs9x9j4rygdg X-HE-Tag: 1728581248-339268 X-HE-Meta: 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 O5e1bcWm DiFH3kyRIsWsvqN7hA3qkLR/5d/MexdyFAy44jy1lNJT0rrS+g0s2E5KsvPc6RnRHVExQ/eQJ2SC7EUL4VTSkBB1P96CIlxa8KGF24yJ1sDUudvtMOlqVT+Z8lPtHS5/8bl3+iaNQ+GjRY3eJg8+zlom9Qg== 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 Thu, Oct 10, 2024 at 12:46:29AM GMT, Roman Gushchin wrote: > On Wed, Oct 09, 2024 at 05:35:50PM -0700, Shakeel Butt wrote: > > The memcg stats are maintained in rstat infrastructure which provides > > very 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 Thanks for the review.