Re: [PATCH v2] mm: vmscan: don't count per-node proactive reclaim as memory pressure

[Ridong Chen <ridong.chen@linux.dev>]

On 10/12/2026 10:29 AM, Vernon Yang wrote:
> From: Vernon Yang <yanglincheng@kylinos.cn>
> 
> When the cgroup has no memory pressure at all, writing to
> /sys/devices/system/nodeX/reclaim triggers proactive reclaim on
> NUMA node, causing increase in the writer cgroup's memory PSI.
> 
> Due to this reclaim is performed in the context of the write(),
> accounted as memory pressure on the writer, like
> commit e22c6ed90aa9 ("mm: memcontrol: don't count limit-setting reclaim
> as memory pressure"). This is unexpected, the similar scenarios (e.g.
> senpai) will continue to occur, only this time it is for the
> /sys/devices/system/nodeX/reclaim knob.
> 
> The Documentation/ABI/stable/sysfs-devices-node documentation also
> notes that "This interface is equivalent to the memcg variant."
> 
> This patch unifies the semantics of the memcg and node interfaces:
> per-node proactive reclaim is no longer counted as memory pressure,
> and the per-node proactive reclaim interface no longer produces
> phantom pressure.
> 
> I ran demo[1] that performs per-node proactive reclaim 10000 times
> in qemu, writer cgroup memory.pressure as follows:
> 
> without patch:
> 
> some avg10=31.53 avg60=13.42 avg300=3.31 total=10602985
> full avg10=31.53 avg60=13.42 avg300=3.31 total=10602985
> 
> with patch:
> 
> some avg10=9.59 avg60=3.41 avg300=0.81 total=2686221
> full avg10=9.59 avg60=3.41 avg300=0.81 total=2686221
> 
> [1] https://github.com/vernon2gh/app_and_module/tree/main/reclaim_node_psi
> 
> Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
> Cc: stable@vger.kernel.org
> Signed-off-by: Vernon Yang <yanglincheng@kylinos.cn>
> ---
> V1 -> V2:
> - Check `sc->proactive` to differentiate between proactive reclaim or
>    page allocation. (Thanks Barry)
> 
> V1 : https://lore.kernel.org/linux-mm/20261005062236.564210-1-vernon2gm@gmail.com/
> ---
>   mm/vmscan.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 91295070ca33..2e9ca5e4c741 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -7994,7 +7994,8 @@ static unsigned long __node_reclaim(struct pglist_data *pgdat,
>   					   sc->gfp_mask);
>   
>   	cond_resched();
> -	psi_memstall_enter(&pflags);
> +	if (!sc->proactive)
> +		psi_memstall_enter(&pflags);
>   	delayacct_freepages_start();
>   	fs_reclaim_acquire(sc->gfp_mask);
>   	/*
> @@ -8011,7 +8012,8 @@ static unsigned long __node_reclaim(struct pglist_data *pgdat,
>   	memalloc_noreclaim_restore(noreclaim_flag);
>   	fs_reclaim_release(sc->gfp_mask);
>   	delayacct_freepages_end();
> -	psi_memstall_leave(&pflags);
> +	if (!sc->proactive)
> +		psi_memstall_leave(&pflags);
>   
>   	trace_mm_vmscan_node_reclaim_end(sc->nr_reclaimed, NULL);
>   

LGTM.

Reviewed-by: Ridong Chen <ridong.chen@linux.dev>
Thanks.

-- 
Best regards
Ridong