From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Down <chris@chrisdown.name>
Subject: Re: [PATCH v3 2/3] mm: Charge active memcg when no mm is set
Date: Thu, 20 Feb 2020 13:35:52 -0500
Message-ID: <20200220183552.GA2181061@chrisdown.name>
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To: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>, Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, Vladimir Davydov <vdavydov.dev@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Hugh Dickins <hughd@google.com>, Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>, Yang Shi <yang.shi@linux.alibaba.com>, Thomas Gleixner <tglx@linutronix.de>, "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:CONTROL GROUP - MEMORY RESOURCE CONTROLLER (MEMCG)" <linux-mm@kvack.org>

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@gmail.com>
>Acked-by: Johannes Weiner <hannes@cmpxchg.org>
>Acked-by: Tejun Heo <tj@kernel.org>

Acked-by: Chris Down <chris@chrisdown.name>

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