Re: [PATCH] mm/mglru: Update MG-LRU proactive reclaim statistics only to memcg

[Yuanchu Xie]

Hi Hao,

On Thu, Jul 17, 2025 at 1:29 AM Hao Jia <jiahao.kernel@xxxxxxxxx> wrote:
>
> From: Hao Jia <jiahao1@xxxxxxxxxxx>
>
> Users can use /sys/kernel/debug/lru_gen to trigger proactive memory reclaim
> of a specified memcg. Currently, statistics such as pgrefill, pgscan and
> pgsteal will be updated to the /proc/vmstat system memory statistics.

This is a debugfs interface and it's not meant for use in production
or provide a stable ABI. Does memory.reclaim not work for your needs?

I'm not against the change; I just hope you don't depend on it
continuing to exist/behave a certain way.

Shakeel's comment is accurate. The lru_gen interface uses the internal
memcg id which is not usually used to interface with the userspace.
Reading this file does show the cgroup path and memcg id association.

>
> This will confuse some system memory pressure monitoring tools, making
> it difficult to determine whether pgscan and pgsteal are caused by
> system-level pressure or by proactive memory reclaim of some specific
> memory cgroup.
>
> Therefore, make this interface behave similarly to memory.reclaim.
> Update proactive memory reclaim statistics only to its memory cgroup.
>
> Signed-off-by: Hao Jia <jiahao1@xxxxxxxxxxx>

The patch looks okay to me too.

Thanks,
Yuanchu