From: Michal Hocko <mhocko@kernel.org>
To: roy.qing.li@gmail.com
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, hannes@cmpxchg.org,
vdavydov@virtuozzo.com
Subject: Re: [PATCH][V2] mm: memcontrol: fix the margin computation in mem_cgroup_margin
Date: Wed, 25 May 2016 17:51:22 +0200 [thread overview]
Message-ID: <20160525155122.GK20132@dhcp22.suse.cz> (raw)
In-Reply-To: <1464068266-27736-1-git-send-email-roy.qing.li@gmail.com>
On Tue 24-05-16 13:37:46, roy.qing.li@gmail.com wrote:
> From: Li RongQing <roy.qing.li@gmail.com>
>
> The margin may be set to the difference value between memory limit and
> memory count firstly. which maybe returned wrongly if memsw.count excess
> memsw.limit, because try_charge forces charging __GFP_NOFAIL allocations,
> which may result in memsw.limit excess. If we are below memory.limit
> and there's nothing to reclaim to reduce memsw.usage, might end up
> looping in try_charge forever.
This is quite hard for me to grasp. What would you say about the
following:
"
mem_cgroup_margin might return memory.limit - memory_count when
the memsw.limit is in excess. This
doesn't happen usually because we do not allow excess on hard limits and
memory.limit <= memsw.limit but __GFP_NOFAIL charges can force the charge
and cause the excess when no memory is really swapable (swap is full or
no anonymous memory is left).
"
>
> Signed-off-by: Li RongQing <roy.qing.li@gmail.com>
> Acked-by: Vladimir Davydov <vdavydov@virtuozzo.com>
> Cc: Michal Hocko <mhocko@suse.com>
Acked-by: Michal Hocko <mhocko@suse.com>
> ---
> mm/memcontrol.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 00981d2..12aaadd 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1090,6 +1090,8 @@ static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
> limit = READ_ONCE(memcg->memsw.limit);
> if (count <= limit)
> margin = min(margin, limit - count);
> + else
> + margin = 0;
> }
>
> return margin;
> --
> 2.1.4
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2016-05-25 15:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-24 5:37 [PATCH][V2] mm: memcontrol: fix the margin computation in mem_cgroup_margin roy.qing.li
2016-05-25 15:51 ` Michal Hocko [this message]
2016-05-26 1:28 ` Li RongQing
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