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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Fri, 17 Jun 2011 11:41:55 -0700
Message-ID: <BANLkTinu=m-Ox9zEwguzth+2H_=MBGvS+Q@mail.gmail.com>
Subject: Re: REGRESSION: Performance regressions from switching anon_vma->lock
 to mutex
To: Peter Zijlstra <peterz@infradead.org>
Cc: Hugh Dickins <hughd@google.com>, 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>,
        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>
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On Fri, Jun 17, 2011 at 11:39 AM, Linus Torvalds
<torvalds@linux-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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