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Date:   Tue, 20 Oct 2020 19:24:02 +0200
From:   Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>
To:     Richard Palethorpe <rpalethorpe@suse.de>
Cc:     Shakeel Butt <shakeelb@google.com>, Linux MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        LTP List <ltp@lists.linux.it>, Roman Gushchin <guro@fb.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>
Subject: Re: [PATCH v3] mm: memcg/slab: Stop reparented obj_cgroups from
 charging root
Message-ID: <20201020172402.GD46039@blackbook>
References: <87lfg2ob83.fsf@suse.de>
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 <CALvZod6FNH3cZfZxLSFXtQR5bV_2Tese0793Ve9rd1YNW22MKg@mail.gmail.com>
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Hi.

On Tue, Oct 20, 2020 at 06:52:08AM +0100, Richard Palethorpe <rpalethorpe@suse.de> wrote:
> I don't think that is relevant as we get the memcg from objcg->memcg
> which is set during reparenting. I suppose however, we can determine if
> the objcg was reparented by inspecting memcg->objcg.
+1

> If we just check use_hierarchy then objects directly charged to the
> memcg where use_hierarchy=0 will not be uncharged. However, maybe it is
> better to check if it was reparented and if use_hierarchy=0.
I think (I had to make a table) the yielded condition would be:

if ((memcg->use_hierarchy && reparented) || (!mem_cgroup_is_root(memcg) && !reparented))
	 __memcg_kmem_uncharge(memcg, nr_pages);

(I admit it's not very readable.)


Michal

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