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

[Nhat Pham]

On Mon, May 11, 2026 at 3:52 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                              | 11 +++++++++--
>  5 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> index 05b664b3b3e8..29a189b18efc 100644
> --- a/Documentation/admin-guide/cgroup-v2.rst
> +++ b/Documentation/admin-guide/cgroup-v2.rst
> @@ -1734,6 +1734,10 @@ 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.
> +
>           zswap_incomp
>                 Number of incompressible pages currently stored in zswap
>                 without compression. These pages could not be compressed to

nit: once we have reached consensus on an interface, can you add
documentation for the new knob in cgroup v2 doc and zswap doc too, and
how it interacts with the other interface (memory.zswap.writeback,
shrinker_enabled sysfs knob).

A kselftest would be very much appreciated too :)