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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9c5a5020-107c-4521-9402-41e614bd2803@huaweicloud.com>
Date: Tue, 16 Dec 2025 08:45:57 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Michal Koutný <mkoutny@...e.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



On 2025/12/16 0:18, Michal Koutný wrote:
> 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.)
> 

Hi Michal,

Thanks for the reminder—I appreciate you pointing that out.

Apologies for missing the links in the cover letter. You can find them in 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

That's correct. To be precise, it only affects root reclaim when lru_gen_enabled() returns true.

Note that the generation LRU can still be enabled via /sys/kernel/mm/lru_gen/enabled even when
CONFIG_LRU_GEN_ENABLED=n.

-- 
Best regards,
Ridong