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

[Ridong Chen]

On 7/13/2026 11:16 PM, Barry Song wrote:
> On Sat, Jul 11, 2026 at 5:12 PM Ridong Chen <ridong.chen@xxxxxxxxx> 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
> >
> > Fixes: 68cd9050d871 ("mm: add swappiness= arg to memory.reclaim")
> > Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
>
> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
>
> 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