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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 17 Jun 2011 09:46:00 -0700
Message-ID: <BANLkTin3onK+43LxODfbu-sdm-pFut0TKw@mail.gmail.com>
Subject: Re: REGRESSION: Performance regressions from switching anon_vma->lock
 to mutex
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To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Tim Chen <tim.c.chen@linux.intel.com>, Andi Kleen <ak@linux.intel.com>, Shaohua Li <shaohua.li@intel.com>, Andrew Morton <akpm@linux-foundation.org>, Hugh Dickins <hughd@google.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, David Miller <davem@davemloft.net>, Martin Schwidefsky <schwidefsky@de.ibm.com>, Russell King <rmk@arm.linux.org.uk>, Paul Mundt <lethal@linux-sh.org>, Jeff Dike <jdike@addtoit.com>, Richard Weinberger <richard@nod.at>, "Luck, Tony" <tony.luck@intel.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, Mel Gorman <mel@csn.ul.ie>, Nick Piggin <npiggin@kernel.dk>, Namhyung Kim <namhyung@gmail.com>, "Shi, Alex" <alex.shi@intel.com>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Rafael J. Wysocki" <rjw@sisk.pl>

On Fri, Jun 17, 2011 at 4:28 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
>
> Something like so? Compiles and runs the benchmark in question.

Oh, and can you do this with a commit log and sign-off, and I'll put
it in my "anon_vma-locking" branch that I have. I'm not going to
actually merge that branch into mainline until I've seen a few more
acks or more testing by Tim.

But if Tim's numbers hold up (-32% to +15% performance by just the
first one, and +15% isn't actually an improvement since tmpfs
read-ahead should have gotten us to +66%), I think we have to do this
just to avoid the performance regression.

                                     Linus

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