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Message-ID: <BANLkTinu=m-Ox9zEwguzth+2H_=MBGvS+Q@mail.gmail.com>
Date: Fri, 17 Jun 2011 11:41:55 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Hugh Dickins <hughd@...gle.com>,
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, Jun 17, 2011 at 11:39 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> Having gone over it a bit more, I actually think I prefer to just
> special-case the allocation instead.
Just to explain my thinking: the thing I disliked most about doing an
allocation while holding the lock wasn't that I thought we would
deadlock on page reclaim. I don't claim that kind of far-sight.
No, the thing I disliked was that if we're low on memory and actually
have to wait, I disliked having the lack of concurrency. I'm ok with
holding the mutex over a few more CPU cycles, but anything longer
might actually hurt throughput. So the patch I just sent out should
fix both the page reclaim deadlock, and avoid any problems with delays
due to holding the critical lock over an expensive allocation.
Linus
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