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

[Chen Ridong <chenridong@huaweicloud.com>]

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