From: Richard Palethorpe <rpalethorpe@suse.de>
To: Shakeel Butt <shakeelb@google.com>
Cc: 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
Date: Tue, 20 Oct 2020 14:49:47 +0100 [thread overview]
Message-ID: <87eeltvwg4.fsf@suse.de> (raw)
In-Reply-To: <87mu0hwik7.fsf@suse.de>
Hello,
Richard Palethorpe <rpalethorpe@suse.de> writes:
> Hello Shakeel,
>
> Shakeel Butt <shakeelb@google.com> writes:
>>>
>>> V3: Handle common case where use_hierarchy=1 and update description.
>>>
>>> mm/memcontrol.c | 7 +++++--
>>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>>> index 6877c765b8d0..34b8c4a66853 100644
>>> --- a/mm/memcontrol.c
>>> +++ b/mm/memcontrol.c
>>> @@ -291,7 +291,7 @@ static void obj_cgroup_release(struct percpu_ref *ref)
>>>
>>> spin_lock_irqsave(&css_set_lock, flags);
>>> memcg = obj_cgroup_memcg(objcg);
>>> - if (nr_pages)
>>> + if (nr_pages && (!mem_cgroup_is_root(memcg) || memcg->use_hierarchy))
>>
>> If we have non-root memcg with use_hierarchy as 0 and this objcg was
>> reparented then this __memcg_kmem_uncharge() can potentially underflow
>> the page counter and give the same warning.
>
> Yes, although the kernel considers such a config to be broken, and
> prints a warning to the log, it does allow it.
Actually this can not happen because if use_hierarchy=0 then the objcg
will be reparented to root.
>
>>
>> We never set root_mem_cgroup->objcg, so, no need to check for root
>
> 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.
>
>> here. I think checking just memcg->use_hierarchy should be sufficient.
>
> 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.
--
Thank you,
Richard.
next prev parent reply other threads:[~2020-10-20 13:49 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-14 19:07 [RFC PATCH] mm: memcg/slab: Stop reparented obj_cgroups from charging root 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
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 [this message]
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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