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

[Muchun Song <muchun.song@linux.dev>]

> 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.