linux-kernel - Re: [patch 1/3] mm: memcontrol: lockless page counters

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Message-ID: <20141014163354.GA23911@phnom.home.cmpxchg.org>
Date:	Tue, 14 Oct 2014 12:33:54 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vladimir Davydov <vdavydov@...allels.com>,
	cgroups@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/3] mm: memcontrol: lockless page counters

On Tue, Oct 14, 2014 at 05:56:47PM +0200, Michal Hocko wrote:
> On Mon 13-10-14 21:46:01, Johannes Weiner wrote:
> > Memory is internally accounted in bytes, using spinlock-protected
> > 64-bit counters, even though the smallest accounting delta is a page.
> > The counter interface is also convoluted and does too many things.
> > 
> > Introduce a new lockless word-sized page counter API, then change all
> > memory accounting over to it.  The translation from and to bytes then
> > only happens when interfacing with userspace.
> > 
> > The removed locking overhead is noticable when scaling beyond the
> > per-cpu charge caches - on a 4-socket machine with 144-threads, the
> > following test shows the performance differences of 288 memcgs
> > concurrently running a page fault benchmark:
> 
> I assume you had root.use_hierarchy = 1, right? Processes wouldn't bounce
> on the same lock otherwise.

Yep.  That's already the default on most distros, and will be in the
kernel in unified hierarchy.

> > Signed-off-by: Johannes Weiner <hannes@...xchg.org>
> 
> You have only missed MAINTAINERS...

Hm, we can add it, but then again scripts/get_maintainer.pl should
already do the right thing.  I find myself using it with --git all the
time to find the people that actually worked on the code recently, not
just the ones listed in there - which might be stale information.

> Acked-by: Michal Hocko <mhocko@...e.cz>

Thank you, Michal!
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