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Date:   Mon, 31 Jan 2022 12:15:19 -0500
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Subject: Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock
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From:   Waiman Long <longman@redhat.com>
To:     Roman Gushchin <guro@fb.com>
Cc:     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>, linux-kernel@vger.kernel.org,
        cgroups@vger.kernel.org, linux-mm@kvack.org,
        Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>
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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?

Thanks,
Longman