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References: <20210402191638.3249835-1-schatzberg.dan@gmail.com> <20210402191638.3249835-3-schatzberg.dan@gmail.com>
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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Sat, 3 Apr 2021 13:47:05 +0800
Message-ID: <CAMZfGtVwxo-UMq8RD_2hpLAbhhYzSkDi_J7kQOJ3yzFz=-5USQ@mail.gmail.com>
Subject: Re: [External] [PATCH 2/3] mm: Charge active memcg when no mm is set
To:     Dan Schatzberg <schatzberg.dan@gmail.com>
Cc:     Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Hugh Dickins <hughd@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <guro@fb.com>, Yang Shi <shy828301@gmail.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        "open list:BLOCK LAYER" <linux-block@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>,
        Chris Down <chris@chrisdown.name>
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On Sat, Apr 3, 2021 at 3:17 AM Dan Schatzberg <schatzberg.dan@gmail.com> wrote:
>
> set_active_memcg() worked for kernel allocations but was silently
> ignored for user pages.
>
> This patch establishes a precedence order for who gets charged:
>
> 1. If there is a memcg associated with the page already, that memcg is
>    charged. This happens during swapin.
>
> 2. If an explicit mm is passed, mm->memcg is charged. This happens
>    during page faults, which can be triggered in remote VMs (eg gup).
>
> 3. Otherwise consult the current process context. If there is an
>    active_memcg, use that. Otherwise, current->mm->memcg.
>
> Previously, if a NULL mm was passed to mem_cgroup_charge (case 3) it
> would always charge the root cgroup. Now it looks up the active_memcg
> first (falling back to charging the root cgroup if not set).
>
> Signed-off-by: Dan Schatzberg <schatzberg.dan@gmail.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> Acked-by: Tejun Heo <tj@kernel.org>
> Acked-by: Chris Down <chris@chrisdown.name>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>

Reviewed-by: Muchun Song <songmuchun@bytedance.com>

Thanks.