Re: [PATCH v2 4/4] mm/mglru: fix anon-only reclaim evicting file pages when swappiness=max

[Qi Zheng <qi.zheng@linux.dev>]

On 7/18/26 9:43 PM, Barry Song wrote:
> On Sat, Jul 18, 2026 at 5:54 PM Ridong Chen <ridong.chen@linux.dev> wrote:
>>
>> From: Ridong Chen <chenridong@xiaomi.com>
>>
>> The previous patch fixes this issue for the traditional LRU, which also
>> exists in MGLRU [1]. Fix this by checking whether swappiness is
>> SWAPPINESS_ANON_ONLY in get_swappiness() first, and returning 0 from
>> get_nr_to_scan() when swappiness is SWAPPINESS_ANON_ONLY and anon pages
>> cannot be reclaimed, to avoid useless work.
> 
> Is this intended to avoid unnecessary work, or to prevent file folios
> from being reclaimed incorrectly?

Based on the test results below, it seems primarily intended to prevent
file pages from being mistakenly reclaimed. Also, bailing out early in
the SWAPPINESS_ANON_ONLY + !can_reclaim_anon_pages case is to avoid
unnecessary work.

Hi Ridong, perhaps the commit message could be clearer. ;)

> 
>>
>> The test result:
>> Before fix:
>>
>>    # cat /sys/kernel/mm/lru_gen/enabled
>>    0x0007
>>    # cat memory.stat
>>    anon 204800
>>    file 67108864
>>    ...
>>    pgsteal_proactive 0
>>    pgscan_proactive 0
>>
>>    # echo "64M swappiness=max" > memory.reclaim
>>    # cat memory.stat
>>    anon 208896
>>    file 0
>>    ...
>>    pgsteal_proactive 16384
>>    pgscan_proactive 16384
>>
>> After fix:
>>
>>    # cat memory.stat
>>    anon 188416
>>    file 67215360
>>    kernel 1970176
>>    ...
>>    pgsteal_proactive 0
>>    pgscan_proactive 0
>>
>>    # echo "64M swappiness=max" > memory.reclaim
>>    -bash: echo: write error: Resource temporarily unavailable
>>    # cat memory.stat
>>    anon 204800
>>    file 67215360
>>    ...
>>    pgsteal_proactive 0
>>    pgscan_proactive 0
>>
>> [1] https://sashiko.dev/#/patchset/20260717113300.214717-1-ridong.chen@linux.dev
>>
>> Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")
>> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
>> ---
>>   mm/vmscan.c | 14 +++++++++++++-
>>   1 file changed, 13 insertions(+), 1 deletion(-)
>>

Overall, this looks good to me.

Acked-by: Qi Zheng <qi.zheng@linux.dev>

Thanks,
Qi