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

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Message-ID: <CABdmKX3iqmPnmSDi=KCy+0QSws+PjLR1jLs8HL-JjorCARM02A@mail.gmail.com>
Date: Wed, 16 Oct 2024 10:17:22 -0700
From: "T.J. Mercier" <tjmercier@...gle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Johannes Weiner <hannes@...xchg.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 2:37 PM Shakeel Butt <shakeel.butt@...ux.dev> 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>

Reviewed-by: T.J. Mercier <tjmercier@...gle.com>