Re: [PATCH -v4 1/4] mm/vmscan: fix anon-only reclaim evicting file pages when swappiness=max

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

On 7/27/2026 6:56 PM, Barry Song wrote:
> On Mon, Jul 27, 2026 at 4:19 PM Michal Hocko <mhocko@suse.com> wrote:
>>
>> On Fri 24-07-26 11:34:32, Ridong wrote:
>>> From: Ridong Chen <chenridong@xiaomi.com>
>>>
>>> As Qi mentioned [1], when swappiness=max (SWAPPINESS_ANON_ONLY) is set,
>>> the reclaim logic is expected to reclaim anonymous pages exclusively.
>>> However, due to the current ordering of checks in get_scan_count(),
>>> file pages may still be evicted if can_reclaim_anon_pages() returns
>>> false, which contradicts the semantics of SWAPPINESS_ANON_ONLY.
>>
>> But if can_reclaim_anon_pages tells us that anonymous pages are not
>> reclaimable then it makes no sense to try that, no? What do you expect
>> to see? An OOM killer?
> 
> This is proactive reclaim rather than direct reclaim, and
> SWAPPINESS_ANON_ONLY is only supported for proactive reclaim. It
> therefore cannot invoke the OOM killer.
> 
> If I understand correctly, this is exactly the issue this patch is
> trying to address. Instead of falling back to reclaiming file folios,
> it returns "bash: echo: write error: Resource temporarily unavailable".
> 
>   After (file cache is left intact):
>      # cat memory.stat
>      anon 200704
>      file 67178496
>      pgscan_proactive 0
>      # echo "64M swappiness=max" > memory.reclaim
>      -bash: echo: write error: Resource temporarily unavailable
>      # cat memory.stat
>      anon 208896
>      file 67178496             <- page cache untouched
>      pgsteal_proactive 0
>      pgscan_proactive 0
> 
> Ridong, please correct me if I am wrong.

Thank you, Barry, it's correct.

-- 
Best regards
Ridong