From: Andrew Morton <akpm@linux-foundation.org>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Michal Hocko <mhocko@kernel.org>,
Johannes Weiner <hannes@cmpxchg.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Shakeel Butt <shakeelb@google.com>
Subject: Re: [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes
Date: Thu, 11 Jan 2018 16:21:34 -0800 [thread overview]
Message-ID: <20180111162134.53aa5a44c59689ec0399db57@linux-foundation.org> (raw)
In-Reply-To: <47856d2b-1534-6198-c2e2-6d2356973bef@virtuozzo.com>
On Thu, 11 Jan 2018 14:59:23 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
> On 01/11/2018 01:31 AM, Andrew Morton wrote:
> > On Wed, 10 Jan 2018 15:43:17 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
> >
> >> mem_cgroup_resize_[memsw]_limit() tries to free only 32 (SWAP_CLUSTER_MAX)
> >> pages on each iteration. This makes practically impossible to decrease
> >> limit of memory cgroup. Tasks could easily allocate back 32 pages,
> >> so we can't reduce memory usage, and once retry_count reaches zero we return
> >> -EBUSY.
> >>
> >> Easy to reproduce the problem by running the following commands:
> >>
> >> mkdir /sys/fs/cgroup/memory/test
> >> echo $$ >> /sys/fs/cgroup/memory/test/tasks
> >> cat big_file > /dev/null &
> >> sleep 1 && echo $((100*1024*1024)) > /sys/fs/cgroup/memory/test/memory.limit_in_bytes
> >> -bash: echo: write error: Device or resource busy
> >>
> >> Instead of relying on retry_count, keep retrying the reclaim until
> >> the desired limit is reached or fail if the reclaim doesn't make
> >> any progress or a signal is pending.
> >>
> >
> > Is there any situation under which that mem_cgroup_resize_limit() can
> > get stuck semi-indefinitely in a livelockish state? It isn't very
> > obvious that we're protected from this, so perhaps it would help to
> > have a comment which describes how loop termination is assured?
> >
>
> We are not protected from this. If tasks in cgroup *indefinitely* generate reclaimable memory at high rate
> and user asks to set unreachable limit, like 'echo 4096 > memory.limit_in_bytes', than
> try_to_free_mem_cgroup_pages() will return non-zero indefinitely.
>
> Is that a big deal? At least loop can be interrupted by a signal, and we don't hold any locks here.
It may be better to detect this condition, give up and return an error?
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next prev parent reply other threads:[~2018-01-12 0:21 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-20 10:24 [PATCH 1/2] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes Andrey Ryabinin
2017-12-20 10:24 ` [PATCH 2/2] mm/memcg: Consolidate mem_cgroup_resize_[memsw]_limit() functions Andrey Ryabinin
2017-12-20 10:33 ` [PATCH 1/2] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes Michal Hocko
2017-12-20 11:32 ` Andrey Ryabinin
2017-12-20 11:34 ` Michal Hocko
2017-12-20 18:15 ` Shakeel Butt
2017-12-21 10:00 ` Andrey Ryabinin
2017-12-20 13:21 ` [PATCH v2 " Andrey Ryabinin
2017-12-20 13:21 ` [PATCH v2 2/2] mm/memcg: Consolidate mem_cgroup_resize_[memsw]_limit() functions Andrey Ryabinin
2017-12-20 13:53 ` [PATCH v2 1/2] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes Michal Hocko
2018-01-09 16:58 ` [PATCH v3 " Andrey Ryabinin
2018-01-09 16:58 ` [PATCH v3 2/2] mm/memcg: Consolidate mem_cgroup_resize_[memsw]_limit() functions Andrey Ryabinin
2018-01-09 17:10 ` Shakeel Butt
2018-01-09 17:26 ` Andrey Ryabinin
2018-01-09 23:26 ` Andrew Morton
2018-01-10 12:43 ` [PATCH v4] mm/memcg: try harder to decrease [memory,memsw].limit_in_bytes Andrey Ryabinin
2018-01-10 22:31 ` Andrew Morton
2018-01-11 11:59 ` Andrey Ryabinin
2018-01-12 0:21 ` Andrew Morton [this message]
2018-01-12 9:08 ` Andrey Ryabinin
2018-01-11 10:42 ` Michal Hocko
2018-01-11 12:21 ` Andrey Ryabinin
2018-01-11 12:46 ` Michal Hocko
2018-01-11 15:23 ` Andrey Ryabinin
2018-01-11 16:29 ` Michal Hocko
2018-01-11 21:59 ` Andrey Ryabinin
2018-01-12 12:24 ` Michal Hocko
2018-01-12 22:57 ` Shakeel Butt
2018-01-15 12:29 ` Andrey Ryabinin
2018-01-15 17:04 ` Shakeel Butt
2018-01-15 12:30 ` Andrey Ryabinin
2018-01-15 12:46 ` Michal Hocko
2018-01-15 12:53 ` Andrey Ryabinin
2018-01-15 12:58 ` Michal Hocko
2018-01-09 17:08 ` [PATCH v3 1/2] " Andrey Ryabinin
2018-01-09 17:22 ` Shakeel Butt
2018-01-19 13:25 ` [PATCH v5 1/2] mm/memcontrol.c: " Andrey Ryabinin
2018-01-19 13:25 ` [PATCH v5 2/2] mm/memcontrol.c: Reduce reclaim retries in mem_cgroup_resize_limit() Andrey Ryabinin
2018-01-19 13:35 ` Michal Hocko
2018-01-19 14:49 ` Shakeel Butt
2018-01-19 15:11 ` Michal Hocko
2018-01-19 15:24 ` Shakeel Butt
2018-01-19 15:31 ` Michal Hocko
2018-02-21 20:17 ` Andrew Morton
2018-02-22 13:50 ` Andrey Ryabinin
2018-02-22 14:09 ` Michal Hocko
2018-02-22 15:13 ` Andrey Ryabinin
2018-02-22 15:33 ` Michal Hocko
2018-02-22 15:38 ` Andrey Ryabinin
2018-02-22 15:44 ` Michal Hocko
2018-02-22 16:01 ` Andrey Ryabinin
2018-02-22 16:30 ` Michal Hocko
2018-01-19 13:32 ` [PATCH v5 1/2] mm/memcontrol.c: try harder to decrease [memory,memsw].limit_in_bytes Michal Hocko
2018-01-25 19:44 ` Andrey Ryabinin
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