Re: [PATCH 00/24] Swapin path refactor for optimization and bugfix

[Kairui Song]

Chris Li <chrisl@xxxxxxxxxx> 于2023年11月21日周二 04:23写道：
>
> Hi Kairui,
>
> On Mon, Nov 20, 2023 at 11:10 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote:
> >
> > On Sun, Nov 19, 2023 at 11:48 AM Kairui Song <ryncsn@xxxxxxxxx> wrote:
> > >
> > > From: Kairui Song <kasong@xxxxxxxxxxx>
> > >
> > > 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?
> >
> > 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.
> >
>
> I was looking at this at patch 23 as well. Will ask more questions in
> the patch thread.
> I would suggest making these two behavior change patches separate out
> from the clean up series to give it more exposure and proper
> discussion.
> Patch 5 and patch 23.
>
> Chris
>

Hi Chris,

Thank you very much for reviewing these details, it's really helpful.

I'll send out new serieses after checking your suggestions on these patches.