linux-kernel - Re: [PATCH -next 0/5] mm/mglru: remove memcg lru

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Message-ID: <oa62a226nagmrqbc23kys3yw3ouxkn5spcizyqqevsuhkurbsv@tvvwqlgu5yum>
Date: Mon, 15 Dec 2025 17:18:49 +0100
From: Michal Koutný <mkoutny@...e.com>
To: Chen Ridong <chenridong@...weicloud.com>
Cc: akpm@...ux-foundation.org, axelrasmussen@...gle.com, 
	yuanchu@...gle.com, weixugc@...gle.com, david@...nel.org, lorenzo.stoakes@...cle.com, 
	Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com, 
	mhocko@...e.com, corbet@....net, hannes@...xchg.org, roman.gushchin@...ux.dev, 
	shakeel.butt@...ux.dev, muchun.song@...ux.dev, zhengqi.arch@...edance.com, 
	linux-mm@...ck.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, lujialin4@...wei.com, zhongjinji@...or.com
Subject: Re: [PATCH -next 0/5] mm/mglru: remove memcg lru

Hi.

On Tue, Dec 09, 2025 at 01:25:52AM +0000, Chen Ridong <chenridong@...weicloud.com> wrote:
> From: Chen Ridong <chenridong@...wei.com>
> 
> The memcg LRU was introduced to improve scalability in global reclaim,
> but its implementation has grown complex and can cause performance
> regressions when creating many memory cgroups [1].
> 
> This series implements mem_cgroup_iter with a reclaim cookie in
> shrink_many() for global reclaim, following the pattern already used in
> shrink_node_memcgs(), an approach suggested by Johannes [1]. The new
> design maintains good fairness across cgroups by preserving iteration
> state between reclaim passes.
> 
> Testing was performed using the original stress test from Yu Zhao [2] on a
> 1 TB, 4-node NUMA system. The results show:

(I think the cover letter somehow lost the targets of [1],[2]. I assume
I could retrieve those from patch 1/5.)


> 
>     pgsteal:
>                                         memcg LRU    memcg iter
>     stddev(pgsteal) / mean(pgsteal)     106.03%       93.20%
>     sum(pgsteal) / sum(requested)        98.10%       99.28%
>     
>     workingset_refault_anon:
>                                         memcg LRU    memcg iter
>     stddev(refault) / mean(refault)     193.97%      134.67%
>     sum(refault)                       1,963,229    2,027,567
> 
> The new implementation shows clear fairness improvements, reducing the
> standard deviation relative to the mean by 12.8 percentage points for
> pgsteal and bringing the pgsteal ratio closer to 100%. Refault counts
> increased by 3.2% (from 1,963,229 to 2,027,567).

Just as a quick clarification -- this isn't supposed to affect regular
(CONFIG_LRU_GEN_ENABLED=n) reclaim, correct?

Thanks,
Michal

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