linux-kernel - Re: [patch] mm: memcontrol: revert use of root_mem_cgroup res

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Message-ID: <20140905135507.GE25641@esperanza>
Date:	Fri, 5 Sep 2014 17:55:07 +0400
From:	Vladimir Davydov <vdavydov@...allels.com>
To:	Johannes Weiner <hannes@...xchg.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Dave Hansen <dave@...1.net>, Michal Hocko <mhocko@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>, Tejun Heo <tj@...nel.org>,
	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [patch] mm: memcontrol: revert use of root_mem_cgroup res_counter

On Fri, Sep 05, 2014 at 08:43:57AM -0400, 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.
> 
> Reported-by: Dave Hansen <dave@...1.net>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> Tested-by: Dave Hansen <dave.hansen@...el.com>
> Acked-by: Michal Hocko <mhocko@...e.cz>

It's a pity we have to revert this nice cleanup, but seems we can't do
anything better right now. FWIW,

Reviewed-by: Vladimir Davydov <vdavydov@...allels.com>
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