From: Vladimir Davydov <vdavydov@virtuozzo.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>, <linux-mm@kvack.org>,
<cgroups@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<kernel-team@fb.com>
Subject: Re: [PATCH] mm: memcontrol: reclaim when shrinking memory.high below usage
Date: Fri, 11 Mar 2016 11:34:40 +0300 [thread overview]
Message-ID: <20160311083440.GI1946@esperanza> (raw)
In-Reply-To: <1457643015-8828-1-git-send-email-hannes@cmpxchg.org>
On Thu, Mar 10, 2016 at 03:50:13PM -0500, Johannes Weiner wrote:
> When setting memory.high below usage, nothing happens until the next
> charge comes along, and then it will only reclaim its own charge and
> not the now potentially huge excess of the new memory.high. This can
> cause groups to stay in excess of their memory.high indefinitely.
>
> To fix that, when shrinking memory.high, kick off a reclaim cycle that
> goes after the delta.
I agree that we should reclaim the high excess, but I don't think it's a
good idea to do it synchronously. Currently, memory.low and memory.high
knobs can be easily used by a single-threaded load manager implemented
in userspace, because it doesn't need to care about potential stalls
caused by writes to these files. After this change it might happen that
a write to memory.high would take long, seconds perhaps, so in order to
react quickly to changes in other cgroups, a load manager would have to
spawn a thread per each write to memory.high, which would complicate its
implementation significantly.
Since, in contrast to memory.max, memory.high definition allows cgroup
to breach it, I believe it would be better if we spawned an asynchronous
reclaim work from the kernel on write to memory.high instead of doing
this synchronously. I guess we could reuse mem_cgroup->high_work for
that.
Thanks,
Vladimir
next prev parent reply other threads:[~2016-03-11 8:35 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-10 20:50 [PATCH] mm: memcontrol: reclaim when shrinking memory.high below usage Johannes Weiner
2016-03-11 7:55 ` Michal Hocko
2016-03-11 8:34 ` Vladimir Davydov [this message]
2016-03-11 8:42 ` Michal Hocko
2016-03-11 9:13 ` Vladimir Davydov
2016-03-11 9:53 ` Michal Hocko
2016-03-11 11:49 ` Vladimir Davydov
2016-03-11 13:39 ` Michal Hocko
2016-03-11 14:01 ` Vladimir Davydov
2016-03-11 14:22 ` Michal Hocko
2016-03-11 14:46 ` Vladimir Davydov
2016-03-16 5:41 ` Johannes Weiner
2016-03-16 14:47 ` Vladimir Davydov
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