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

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Date:	Fri, 17 Jun 2011 19:55:19 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	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

On Fri, 2011-06-17 at 10:41 -0700, Hugh Dickins wrote:
> > The only thing I don't love about the batching is that we now do hold
> > the lock over some situations where we _could_ have allowed
> > concurrency (notably some avc allocations), but I think it's a good
> > trade-off. And walking the list twice at unlink_anon_vmas() should be
> > basically free.
> 
> Applying load with those two patches applied (combined patch shown at
> the bottom, in case you can tell me I misunderstood what to apply,
> and have got the wrong combination on), lockdep very soon protested.

Gah, of course. Its exactly the case Linus mentioned not loving. We can
get reclaim recursion due to the avc allocation, we hold anon_vma->mutex
while doing a (blocking) allocation, and reclaim can end up trying to
obtain said lock trying to free some memory.

Bugger. /me goes investigate

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