linux-kernel - Re: [PATCH 2/3] mm: Charge active memcg when no mm is set

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Date:   Thu, 3 Jun 2021 09:53:16 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Dan Schatzberg <schatzberg.dan@...il.com>,
        Muchun Song <songmuchun@...edance.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Chris Down <chris@...isdown.name>
Subject: Re: [PATCH 2/3] mm: Charge active memcg when no mm is set

On Thu, Jun 3, 2021 at 7:57 AM Dan Schatzberg <schatzberg.dan@...il.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@...il.com>
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Acked-by: Tejun Heo <tj@...nel.org>
> Acked-by: Chris Down <chris@...isdown.name>
> Acked-by: Jens Axboe <axboe@...nel.dk>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>

Can you please rebase over the latest mm tree? Specifically over
Muchun's patch "mm: memcontrol: bail out early when !mm in
get_mem_cgroup_from_mm".