Re: [PATCH v2 2/2] mm: vmscan: fix node reclaim ignoring swappiness parameter

[Qi Zheng]

On 7/16/26 11:17 AM, Ridong wrote:
> From: Ridong Chen <chenridong@xxxxxxxxxx>
>
> 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
>
> Cc: stable@xxxxxxxxxxxxxxx # 6.17+
> Fixes: b980077899ea ("mm: introduce per-node proactive reclaim interface")
> Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
> Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
> ---
>   mm/vmscan.c | 19 +++++++------------
>   1 file changed, 7 insertions(+), 12 deletions(-)

Thanks for fixing this!

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