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

[Chen Ridong <chenridong@huaweicloud.com>]

On 2025/12/9 9:25, Chen Ridong 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:
> 
>     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).
> 
> To simplify review:
> 1. Patch 1 uses mem_cgroup_iter with reclaim cookie in shrink_many()
> 2. Patch 2 removes the now-unused memcg LRU code
> 3. Patches 3–5 combine shrink_many and shrink_node_memcgs
>    (This reorganization is clearer after switching to mem_cgroup_iter)
> 
> ---
> 
> Changes from RFC series:
> 1. Updated the test result data.
> 2. Added patches 3–5 to combine shrink_many and shrink_node_memcgs.
> 
> RFC: https://lore.kernel.org/all/20251204123124.1822965-1-chenridong@huaweicloud.com/
> 
> Chen Ridong (5):
>   mm/mglru: use mem_cgroup_iter for global reclaim
>   mm/mglru: remove memcg lru
>   mm/mglru: extend shrink_one for both lrugen and non-lrugen
>   mm/mglru: combine shrink_many into shrink_node_memcgs
>   mm/mglru: factor lrugen state out of shrink_lruvec
> 
>  Documentation/mm/multigen_lru.rst |  30 ---
>  include/linux/mmzone.h            |  89 --------
>  mm/memcontrol-v1.c                |   6 -
>  mm/memcontrol.c                   |   4 -
>  mm/mm_init.c                      |   1 -
>  mm/vmscan.c                       | 332 ++++--------------------------
>  6 files changed, 44 insertions(+), 418 deletions(-)
> 

Hello all,

There's a warning from the kernel test robot, and I would like to update the series to fix it along
with any feedback from your reviews.

I'd appreciate it if you could take a look at this patch series when convenient.

Hi Shakeel, I would be very grateful if you could review patches 3-5. They combine shrink_many and
shrink_node_memcgs as you suggested — does that look good to you?

-- 
Best regards,
Ridong