Re: [PATCH 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

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

On 7/13/2026 11:16 PM, Barry Song wrote:
> On Sat, Jul 11, 2026 at 5:12 PM Ridong Chen <ridong.chen@linux.dev> wrote:
>>
>> From: Ridong Chen <chenridong@xiaomi.com>
>>
>> sc_swappiness() had two separate definitions depending on
>> CONFIG_MEMCG. The !CONFIG_MEMCG variant simply returned
>> vm_swappiness, ignoring the proactive_swappiness value passed
>> through scan_control. This caused the swappiness parameter
>> written to /sys/devices/system/node/nodeX/reclaim to have no
>> effect when CONFIG_MEMCG is disabled.
>>
>> Fix this by consolidating sc_swappiness() into a single definition
>> that checks sc->proactive_swappiness first, then falls back to
>> mem_cgroup_swappiness() which already handles both CONFIG_MEMCG
>> and !CONFIG_MEMCG.
>>
>> Before fix (swappiness=max ignored, mostly file pages reclaimed):
>>
>>      # cat /proc/sys/vm/swappiness
>>      60
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 1840
>>      pgsteal_anon 25
>>      pgsteal_file 1815
>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 18013
>>      pgsteal_anon 337
>>      pgsteal_file 17676
>>
>> After fix (swappiness=max honored, anon pages reclaimed as expected):
>>
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 0
>>      pgsteal_anon 0
>>      pgsteal_file 0
>>      # echo "64M swappiness=max" > /sys/devices/system/node/node0/reclaim
>>      # cat /proc/vmstat | grep pgsteal
>>      pgsteal_kswapd 0
>>      pgsteal_direct 0
>>      pgsteal_khugepaged 0
>>      pgsteal_proactive 16283
>>      pgsteal_anon 16283
>>      pgsteal_file 0
>>
>> Fixes: 68cd9050d871 ("mm: add swappiness= arg to memory.reclaim")
>> Signed-off-by: Ridong Chen <chenridong@xiaomi.com>
> 
> Reviewed-by: Barry Song <baohua@kernel.org>
> 
> As pointed out by Johannes, the Fixes tag should be
> b980077899ea.

Hi Johannes and Barry,

Thank you for your review. You are right, will update it.

-- 
Best regards
Ridong