Re: [PATCH v3 3/4] memcg: bail out proactive reclaim when memcg is dying

[Jiayuan Chen]

On 7/2/26 8:02 PM, Jiayuan Chen wrote:
> From: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
>
> Proactive reclaim via memory.reclaim can run for a long time - swap I/O
> or thrashing again dominating the latency - and delays cgroup removal in
> the same way.
>
> Mitigate this by stopping the reclaim once memcg_is_dying().
>
> Cc: Jiayuan Chen <jiayuan.chen@xxxxxxxxx>
> Reported-by: Zhou Yingfu <yingfu.zhou@xxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: Jiayuan Chen <jiayuan.chen@xxxxxxxxxx>
> ---
>   mm/vmscan.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 754c5f5d716a..6ae61be2fab8 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -7912,6 +7912,10 @@ int user_proactive_reclaim(char *buf,
>   		if (signal_pending(current))
>   			return -EINTR;
>   
> +		/* cgroup_rmdir() waits for us with cgroup_mutex held. */
> +		if (memcg && memcg_is_dying(memcg))
> +			return -EAGAIN;
> +
>   		/*
>   		 * This is the final attempt, drain percpu lru caches in the
>   		 * hope of introducing more evictable pages.



The issuse reported by Ai is benign:
https://sashiko.dev/#/patchset/20260702120235.376752-1-jiayuan.chen%40linux.dev

We have multiple break points to return in 
try_to_free_pages::do_try_to_free_pages
'''

    static unsigned long do_try_to_free_pages()
    {

        retry:
            do {

                shrink_zones(zonelist, sc);

                // break 1
                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
                    break;

            } while (--sc->priority >= 0); // at most 12 
times(DEF_PRIORITY)


            // break 2
            if (sc->nr_reclaimed)
                return sc->nr_reclaimed;

            // retry twice logic
            ...
    }
'''