linux-kernel - Re: REGRESSION: Performance regressions from switching anon

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Date:	Wed, 15 Jun 2011 09:18:27 -0700
From:	Andi Kleen <ak@...ux.intel.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Shaohua Li <shaohua.li@...el.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	David Miller <davem@...emloft.net>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Russell King <rmk@....linux.org.uk>,
	Paul Mundt <lethal@...ux-sh.org>,
	Jeff Dike <jdike@...toit.com>,
	Richard Weinberger <richard@....at>,
	"Luck, Tony" <tony.luck@...el.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mel@....ul.ie>, Nick Piggin <npiggin@...nel.dk>,
	Namhyung Kim <namhyung@...il.com>,
	"Shi, Alex" <alex.shi@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: REGRESSION: Performance regressions from switching
 anon_vma->lock to mutex

> 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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