linux-kernel - Re: [PATCH mm-new v2] mm/memcontrol: Flush stats when write stat file

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Message-ID: <6kh6hle2xp75hrtikasequ7qvfyginz7pyttltx6pkli26iir5@oqjmglatjg22>
Date: Wed, 5 Nov 2025 17:19:02 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Leon Huang Fu <leon.huangfu@...pee.com>
Cc: linux-mm@...ck.org, hannes@...xchg.org, mhocko@...nel.org, 
	roman.gushchin@...ux.dev, muchun.song@...ux.dev, akpm@...ux-foundation.org, 
	joel.granados@...nel.org, jack@...e.cz, laoar.shao@...il.com, mclapinski@...gle.com, 
	kyle.meyer@....com, corbet@....net, lance.yang@...ux.dev, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, Yosry Ahmed <yosry.ahmed@...ux.dev>, 
	JP Kobryn <inwardvessel@...il.com>
Subject: Re: [PATCH mm-new v2] mm/memcontrol: Flush stats when write stat file

+Yosry, JP

On Wed, Nov 05, 2025 at 03:49:16PM +0800, Leon Huang Fu wrote:
> On high-core count systems, memory cgroup statistics can become stale
> due to per-CPU caching and deferred aggregation. Monitoring tools and
> management applications sometimes need guaranteed up-to-date statistics
> at specific points in time to make accurate decisions.

Can you explain a bit more on your environment where you are seeing
stale stats? More specifically, how often the management applications
are reading the memcg stats and if these applications are reading memcg
stats for each nodes of the cgroup tree.

We force flush all the memcg stats at root level every 2 seconds but it
seems like that is not enough for your case. I am fine with an explicit
way for users to flush the memcg stats. In that way only users who want
to has to pay for the flush cost.