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Date: Fri, 17 Jun 2011 00:58:03 +0200
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [GIT PULL] Re: REGRESSION: Performance regressions from
 switching anon_vma->lock to mutex
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To: Andi Kleen <ak@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Linus Torvalds <torvalds@linux-foundation.org>, Peter Zijlstra <peterz@infradead.org>, Tim Chen <tim.c.chen@linux.intel.com>, Andrew Morton <akpm@linux-foundation.org>, Hugh Dickins <hughd@google.com>, KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>, 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>, Tony Luck <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>, shaohua.li@intel.com, alex.shi@intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, "Rafael J. Wysocki" <rjw@sisk.pl>


* Andi Kleen <ak@linux.intel.com> wrote:

> > There's a crazy solution for that: the idle thread could process 
> > RCU callbacks carefully, as if it was running user-space code.
> 
> In Ben's kernel NFS server case the system may not be idle.

An always-100%-busy NFS server is very unlikely, but even in the 
hypothetical case a kernel NFS server is really performing system 
calls from a kernel thread in essence. If it doesn't do it explicitly 
then its main loop can easily include a "check RCU callbacks" call.

Thanks,

	Ingo

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