linux-kernel - Re: [PATCH v3 2/3] mm: Charge active memcg when no mm is set

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Message-ID: <20200220183552.GA2181061@chrisdown.name>
Date:   Thu, 20 Feb 2020 13:35:52 -0500
From:   Chris Down <chris@...isdown.name>
To:     Dan Schatzberg <schatzberg.dan@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>, Roman Gushchin <guro@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "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:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" 
        <linux-mm@...ck.org>
Subject: Re: [PATCH v3 2/3] mm: Charge active memcg when no mm is set

Dan Schatzberg writes:
>memalloc_use_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 it has configured
>   a current->active_memcg, use that. Otherwise, current->mm->memcg.
>
>Previously, if a NULL mm was passed to mem_cgroup_try_charge (case 3) it
>would always charge the root cgroup. Now it looks up the current
>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>

Thanks! The clarification the v2 thread for this made things clear to me.