Re: [PATCH v3 3/4] mm/zswap: Add per-memcg stat for proactive writeback

[Hao Jia]

On 2026/5/30 04:01, Nhat Pham wrote:
> On Tue, May 26, 2026 at 4:46 AM Hao Jia <jiahao.kernel@xxxxxxxxx> wrote:
> > From: Hao Jia <jiahao1@xxxxxxxxxxx>
> >
> > Currently, zswap writeback can be triggered by either the pool limit
> > being hit or by the proactive writeback mechanism. However, the
> > existing 'zswpwb' metric in memory.stat and /proc/vmstat counts all
> > written back pages, making it difficult to distinguish between pages
> > written back due to the pool limit and those written back proactively.
> >
> > Add a new statistic 'zswpwb_proactive' to memory.stat and /proc/vmstat.
> > This counter tracks the number of pages written back due to proactive
> > writeback. This allows users to better monitor and tune the proactive
> > writeback mechanism.
> >
> > Signed-off-by: Hao Jia <jiahao1@xxxxxxxxxxx>
> > ---
> >   Documentation/admin-guide/cgroup-v2.rst |  4 +++
> >   include/linux/vm_event_item.h           |  1 +
> >   mm/memcontrol.c                         |  1 +
> >   mm/vmstat.c                             |  1 +
> >   mm/zswap.c                              | 41 ++++++++++++++++++-------
> >   5 files changed, 37 insertions(+), 11 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index 6564abf0dec5..7d65aef83f7b 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1748,6 +1748,10 @@ The following nested keys are defined.
> >            zswpwb
> >                  Number of pages written from zswap to swap.
> >
> > +         zswpwb_proactive
> > +               Number of pages written from zswap to swap by proactive
> > +               writeback. This is a subset of zswpwb.
> > +
>
> nit: I think this is specifically the zswap_writeback_only mode right?
>
> Technically, normal proactive reclaim (memory.reclaim) can also hit zswap :)
>
> Maybe some clarification here?

Thanks for the review. I will clarify this further in the next version.

Thanks,
Hao