linux-kernel - Re: regression caused by cgroups optimization in 3.17-rc2

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Date:	Thu, 04 Sep 2014 13:50:34 -0700
From:	Dave Hansen <dave@...1.net>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Michal Hocko <mhocko@...e.com>, Hugh Dickins <hughd@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	Andrew Morton <akpm@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: regression caused by cgroups optimization in 3.17-rc2

On 09/04/2014 08:08 AM, Johannes Weiner wrote:
> Dave Hansen reports a massive scalability regression in an uncontained
> page fault benchmark with more than 30 concurrent threads, which he
> bisected down to 05b843012335 ("mm: memcontrol: use root_mem_cgroup
> res_counter") and pin-pointed on res_counter spinlock contention.
> 
> That change relied on the per-cpu charge caches to mostly swallow the
> res_counter costs, but it's apparent that the caches don't scale yet.
> 
> Revert memcg back to bypassing res_counters on the root level in order
> to restore performance for uncontained workloads.

A quick sniff test shows performance coming back to what it was around
3.16 with this patch.  I'll run a more thorough set of tests and verify
that it's working well.


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