Messages in this thread | | | Date | Mon, 31 Jan 2022 12:25:05 -0500 | Subject | Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock | From | Waiman Long <> |
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On 1/31/22 12:19, Roman Gushchin wrote: > On Mon, Jan 31, 2022 at 12:15:19PM -0500, Waiman Long wrote: >> On 1/31/22 12:09, Waiman Long wrote: >>> On 1/31/22 12:01, Roman Gushchin wrote: >>>> On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote: >>>>> On 10/1/21 19:51, Roman Gushchin wrote: >>>>>> On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote: >>>>>>> When freeing a page associated with an offlined memcg, refill_stock() >>>>>>> will put it into local stock delaying its demise until another memcg >>>>>>> comes in to take its place in the stock. To avoid that, we now check >>>>>>> for offlined memcg and go directly in this case to the slowpath for >>>>>>> the uncharge via the repurposed cancel_charge() function. >>>>>> Hi Waiman! >>>>>> >>>>>> I'm afraid it can make a cleanup of a dying cgroup slower: for every >>>>>> released page we'll potentially traverse the whole cgroup tree and >>>>>> decrease atomic page counters. >>>>>> >>>>>> I'm not sure I understand the benefits we get from this change which >>>>>> do justify the slowdown on the cleanup path. >>>>>> >>>>>> Thanks! >>>>> I was notified of a lockdep splat that this patch may help to prevent. >>>> Would you mind to test this patch: >>>> https://www.spinics.net/lists/cgroups/msg31244.html ? >>>> >>>> It should address this dependency. >>> Thanks for the pointer. I believe that your patch should be able to >>> address this circular locking dependency. >>> >>> Feel free to add my >>> >>> Reviewed-by: Waiman Long <longman@redhat.com> >> BTW, have you posted it to lkml? If not, would you mind doing so? > Not yet. > > I was waiting for Alexander to confirm that it resolves the originally reported > issue. I just pinged him, will wait for tomorrow and post the patch in any case. > > Thanks!
I see. This is not a problem that is easily reproducible. You need to hit the right timing for the lockdep splat to appear.
Regards, Longman
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