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

[Qi Zheng]

On 7/18/26 9:43 PM, Barry Song wrote:
> On Sat, Jul 18, 2026 at 5:54 PM Ridong Chen <ridong.chen@xxxxxxxxx> wrote:
> > From: Ridong Chen <chenridong@xxxxxxxxxx>
> >
> > 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@xxxxxxxxx
> >
> > Fixes: 68a1436bde00 ("mm: add swappiness=max arg to memory.reclaim for only anon reclaim")
> > Signed-off-by: Ridong Chen <chenridong@xxxxxxxxxx>
> > ---
> >   mm/vmscan.c | 14 +++++++++++++-
> >   1 file changed, 13 insertions(+), 1 deletion(-)

Overall, this looks good to me.

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

Thanks,
Qi