linux-kernel - Re: [PATCH v1 3/3] cgroup/rstat: introduce ratelimited rstat flushing

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Date: Thu, 18 Apr 2024 11:15:31 -1000
From: Tejun Heo <tj@...nel.org>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: Jesper Dangaard Brouer <hawk@...nel.org>, hannes@...xchg.org,
	lizefan.x@...edance.com, cgroups@...r.kernel.org,
	longman@...hat.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, shakeel.butt@...ux.dev,
	kernel-team@...udflare.com,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	mhocko@...nel.org, Wei Xu <weixugc@...gle.com>
Subject: Re: [PATCH v1 3/3] cgroup/rstat: introduce ratelimited rstat flushing

Hello, Yosry.

On Thu, Apr 18, 2024 at 02:00:28PM -0700, Yosry Ahmed wrote:
..
> I think this is an artifact of different subsystems sharing the same
> rstat tree for no specific reason. I think almost all flushing calls
> really need the stats from one subsystem after all.
>
> If we have separate trees, lock contention gets slightly better as
> different subsystems do not compete. We can also have different
> subsystems "customize" their trees, for e.g. by setting different
> time-based or magnitude-based rate-limiting thresholds.
> 
> I know this is a bigger lift, just thinking out loud :)

I have no objection to separating out rstat trees so that it has
per-controller tracking. However, the high frequency source of updates are
cpu and memory, which tend to fire together, and the only really high
frequency consumer seems to be memory, so I'm not too sure how much benefit
separating the trees out would bring.

Thanks.

-- 
tejun