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

Chen Ridong
2025-12-16T00:46:02Z

On 2025/12/16 0:18, Michal Koutný wrote:
> Hi.
>
> On Tue, Dec 09, 2025 at 01:25:52AM +0000, Chen Ridong <chenridong@huaweicloud.com> wrote:
>> From: Chen Ridong <chenridong@huawei.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