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From: Richard Palethorpe <rpalethorpe@suse.de>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Roman Gushchin <guro@fb.com>,
	ltp@lists.linux.it, Johannes Weiner <hannes@cmpxchg.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shakeel Butt <shakeelb@google.com>,
	Christoph Lameter <cl@linux.com>,
	Michal Hocko <mhocko@kernel.org>, Tejun Heo <tj@kernel.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from charging root
Date: Fri, 16 Oct 2020 11:41:43 +0100
Message-ID: <87sgaesba0.fsf@suse.de> (raw)
In-Reply-To: <20201016094702.GA95052@blackbook>

Hello Michal,

Michal Koutný <mkoutny@suse.com> writes:

> Hello.
>
> On Wed, Oct 14, 2020 at 08:07:49PM +0100, Richard Palethorpe <rpalethorpe@suse.com> wrote:
>> SLAB objects which outlive their memcg are moved to their parent
>> memcg where they may be uncharged. However if they are moved to the
>> root memcg, uncharging will result in negative page counter values as
>> root has no page counters.
> Why do you think those are reparented objects? If those are originally
> charged in a non-root cgroup, then the charge value should be propagated up the
> hierarchy, including root memcg, so if they're later uncharged in root
> after reparenting, it should still break even. (Or did I miss some stock
> imbalance?)

I traced it and can see they are reparented objects and that the root
groups counters are zero (or negative if I run madvise06 multiple times)
before a drain takes place. I'm guessing this is because the root group
has 'use_hierachy' set to false so that the childs page_counter parents
are set to NULL. However I will check, because I'm not sure about
either.

>
> (But the patch seems justifiable to me as objects (not)charged directly to
> root memcg may be incorrectly uncharged.)
>
> Thanks,
> Michal


-- 
Thank you,
Richard.


  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-14 19:07 Richard Palethorpe
2020-10-14 20:08 ` Roman Gushchin
2020-10-16  5:40   ` Richard Palethorpe
2020-10-16  9:47 ` Michal Koutný
2020-10-16 10:41   ` Richard Palethorpe [this message]
2020-10-16 15:05     ` Richard Palethorpe
2020-10-16 17:26       ` Michal Koutný
2020-10-16 14:53   ` Johannes Weiner
2020-10-16 17:02     ` Roman Gushchin
2020-10-16 17:15     ` Michal Koutný
2020-10-19  8:45       ` Richard Palethorpe
2020-10-19  9:58         ` [PATCH v3] " Richard Palethorpe
2020-10-19 16:58           ` Shakeel Butt
2020-10-20  5:52             ` Richard Palethorpe
2020-10-20 13:49               ` Richard Palethorpe
2020-10-20 16:56                 ` Shakeel Butt
2020-10-21 20:32                   ` Roman Gushchin
2020-10-20 17:24               ` Michal Koutný
2020-10-22  7:04                 ` Richard Palethorpe
2020-10-22 12:28                   ` [PATCH v4] " Richard Palethorpe
2020-10-22 16:37                     ` Shakeel Butt
2020-10-22 17:25                       ` Roman Gushchin
2020-10-22 23:59                         ` Shakeel Butt
2020-10-23  0:40                           ` Roman Gushchin
2020-10-23 15:44                             ` Johannes Weiner
2020-10-23 16:41                             ` Shakeel Butt
2020-10-26  7:32                             ` Richard Palethorpe
2020-10-26 23:14                               ` Roman Gushchin
2020-10-19 22:28       ` [RFC PATCH] " Roman Gushchin
2020-10-20  6:04         ` Richard Palethorpe
2020-10-20 12:02           ` Richard Palethorpe
2020-10-20 14:48         ` Richard Palethorpe
2020-10-20 16:27         ` Michal Koutný
2020-10-20 17:07           ` Roman Gushchin
2020-10-20 18:18             ` Johannes Weiner
2020-10-21 19:33               ` Roman Gushchin
2020-10-23 16:30                 ` Johannes Weiner
2020-11-10  1:27                   ` Roman Gushchin
2020-11-10 15:11                     ` Shakeel Butt
2020-11-10 19:13                       ` Roman Gushchin
2020-11-20 17:46                       ` Michal Koutný
2020-11-03 13:22                 ` Michal Hocko
2020-11-03 21:30                   ` Roman Gushchin
2020-10-20 16:55         ` Shakeel Butt
2020-10-20 17:17           ` Roman Gushchin

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