linux-kernel - Re: [PATCH v2] memcg: add tracing for memcg stat updates

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Message-ID: <20241015215236.GA1052@cmpxchg.org>
Date: Tue, 15 Oct 2024 17:52:36 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Steven Rostedt <rostedt@...dmis.org>,
	JP Kobryn <inwardvessel@...il.com>,
	Yosry Ahmed <yosryahmed@...gle.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>,
	Michal Hocko <mhocko@...e.com>,
	Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v2] memcg: add tracing for memcg stat updates

On Tue, Oct 15, 2024 at 02:37:21PM -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 <shakeel.butt@...ux.dev>
> Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>
> Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Muchun Song <songmuchun@...edance.com>
> Cc: JP Kobryn <inwardvessel@...il.com>
> Cc: Steven Rostedt (Google) <rostedt@...dmis.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: Johannes Weiner <hannes@...xchg.org>