Re: [PATCH 1/7] mm/swap, workingset: make anon workingset nodes memcg aware

[Kairui Song <ryncsn@gmail.com>]

On Wed, Jul 17, 2024 at 11:25 AM Muchun Song <muchun.song@linux.dev> wrote:
> > On Jun 25, 2024, at 01:53, Kairui Song <ryncsn@gmail.com> wrote:
> >
> > From: Kairui Song <kasong@tencent.com>
> >
> > Currently, the (shadow) nodes of the swap cache are not accounted to
> > their corresponding memory cgroup, instead, they are all accounted
> > to the root cgroup. This leads to inaccurate accounting and
> > ineffective reclaiming.
> >
> > This issue is similar to commit 7b785645e8f1 ("mm: fix page cache
> > convergence regression"), where page cache shadow nodes were incorrectly
> > accounted. That was due to the accidental dropping of the accounting
> > flag during the XArray conversion in commit a28334862993
> > ("page cache: Finish XArray conversion").
> >
> > However, this fix has a different cause. Swap cache shadow nodes were
> > never accounted even before the XArray conversion, since they did not
> > exist until commit 3852f6768ede ("mm/swapcache: support to handle the
> > shadow entries"), which was years after the XArray conversion. Without
> > shadow nodes, swap cache nodes can only use a very small amount of memory
> > and so reclaiming is not very important.
> >
> > But now with shadow nodes, if a cgroup swaps out a large amount of
> > memory, it could take up a lot of memory.
> >
> > This can be easily fixed by adding proper flags and LRU setters.
> >
> > Signed-off-by: Kairui Song <kasong@tencent.com>
>
> I haven't looked at the details of this patch yet, but I think it is not
> related to this series, it could be as an individual patch (If it is a real
> problem, I think it will be quickly and easily merged).
>
> Thanks.
>

The gain of this patch is not as big as being part of the series, but
yes, it can be sent independently.