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
