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Message-ID: <CAMgjq7DgHvcU6gTWhzPY8By8DCx5TzYViKaiuSSxh-zofuV1HQ@mail.gmail.com>
Date: Wed, 22 Nov 2023 14:43:02 +0800
From: Kairui Song <ryncsn@...il.com>
To: Yosry Ahmed <yosryahmed@...gle.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
"Huang, Ying" <ying.huang@...el.com>,
David Hildenbrand <david@...hat.com>,
Hugh Dickins <hughd@...gle.com>,
Johannes Weiner <hannes@...xchg.org>,
Matthew Wilcox <willy@...radead.org>,
Michal Hocko <mhocko@...e.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/24] Swapin path refactor for optimization and bugfix
Yosry Ahmed <yosryahmed@...gle.com> 于2023年11月21日周二 03:18写道:
>
> On Sun, Nov 19, 2023 at 11:48 AM Kairui Song <ryncsn@...il.com> wrote:
> >
> > From: Kairui Song <kasong@...cent.com>
> >
> > This series tries to unify and clean up the swapin path, fixing a few
> > issues with optimizations:
> >
> > 1. Memcg leak issue: when a process that previously swapped out some
> > migrated to another cgroup, and the origianl cgroup is dead. If we
> > do a swapoff, swapped in pages will be accounted into the process
> > doing swapoff instead of the new cgroup. This will allow the process
> > to use more memory than expect easily.
> >
> > This can be easily reproduced by:
> > - Setup a swap.
> > - Create memory cgroup A, B and C.
> > - Spawn process P1 in cgroup A and make it swap out some pages.
> > - Move process P1 to memory cgroup B.
> > - Destroy cgroup A.
> > - Do a swapoff in cgroup C
> > - Swapped in pages is accounted into cgroup C.
> >
> > This patch will fix it make the swapped in pages accounted in cgroup B.
> >
>
> I guess this only works for anonymous memory and not shmem, right?
Hi Yosry,
Yes, this patch only changed the charge target for anon page.
>
> I think tying memcg charges to a process is not something we usually
> do. Charging the pages to the memcg of the faulting process if the
> previous owner is dead makes sense, it's essentially recharging the
> memory to the new owner. Swapoff is indeed a special case, since the
> faulting process is not the new owner, but an admin process or so. I
> am guessing charging to the new memcg of the previous owner might make
> sense in this case, but it is a change of behavior.
After discuss with others I also found this is a controversial issue,
will send separate series for this, I think it needs more discuss.
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