From: Shakeel Butt <shakeelb@google.com>
To: Waiman Long <longman@redhat.com>
Cc: Roman Gushchin <guro@fb.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@suse.cz>,
LKML <linux-kernel@vger.kernel.org>,
Cgroups <cgroups@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
Muchun Song <songmuchun@bytedance.com>
Subject: Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock
Date: Mon, 31 Jan 2022 10:00:24 -0800 [thread overview]
Message-ID: <CALvZod6_L1Q1xnjx26cgNgXHhpH=Mvdkk98f2=AAo=euwYY62Q@mail.gmail.com> (raw)
In-Reply-To: <9abc9cb8-8734-90b0-c495-8df89c7bb579@redhat.com>
On Mon, Jan 31, 2022 at 9:25 AM Waiman Long <longman@redhat.com> wrote:
>
> 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.
I agree here. The patch on its own has merits as it is reducing
dependency on an unrelated lock.
next prev parent reply other threads:[~2022-01-31 18:00 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-01 19:09 [PATCH 0/3] mm, memcg: Miscellaneous cleanups Waiman Long
2021-10-01 19:09 ` [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock Waiman Long
2021-10-01 21:17 ` kernel test robot
2021-10-01 23:06 ` kernel test robot
2021-10-01 23:51 ` Roman Gushchin
2021-10-02 1:54 ` Waiman Long
2022-01-31 3:55 ` Waiman Long
2022-01-31 17:01 ` Roman Gushchin
2022-01-31 17:09 ` Waiman Long
2022-01-31 17:15 ` Waiman Long
2022-01-31 17:19 ` Roman Gushchin
2022-01-31 17:25 ` Waiman Long
2022-01-31 18:00 ` Shakeel Butt [this message]
2022-01-31 17:15 ` Roman Gushchin
2021-10-01 19:09 ` [PATCH 2/3] mm, memcg: Remove obsolete memcg_free_kmem() Waiman Long
2021-10-02 0:01 ` Roman Gushchin
2021-10-02 2:03 ` Waiman Long
2021-10-01 19:09 ` [PATCH 3/3] mm, memcg: Ensure valid memcg from objcg within a RCU critical section Waiman Long
2021-10-01 20:24 ` Shakeel Butt
2021-10-01 20:34 ` Waiman Long
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