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Date: Wed, 15 Jun 2011 09:18:27 -0700
From: Andi Kleen <ak@linux.intel.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: Shaohua Li <shaohua.li@intel.com>, Tim Chen <tim.c.chen@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@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>

> Good spot that certainly isn't plain .39.

True.

> 
> It looks like those (http://marc.info/?l=linux-mm&m=130533041726258) are
> similar to Linus' patch, except Linus takes the hard line that the root

One difference to Linus' patch is that it does batching for both fork+exit.
I suspect Linus' patch could probably too.

But the fork+exit patch only improved things slightly, it's very unlikely to 
recover 52%. Maybe the overall locking here needs to be revisited.

And in general it looks like blind conversion from spinlock to mutex
is a bad idea right now.

-Andi

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