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Date: Thu, 16 Jun 2011 14:02:16 -0700
From: Andi Kleen <ak@linux.intel.com>
Subject: Re: [GIT PULL] Re: REGRESSION: Performance regressions from
 switching anon_vma->lock to mutex
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To: Ingo Molnar <mingo@elte.hu>
Cc: "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>, 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>, 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>

> So user-return notifiers ought to be the ideal platform for that, 
> right? We don't even have to touch the scheduler: anything that 
> schedules will eventually return to user-space, at which point the 
> RCU GC magic can run.

That's not necessarily true. Consider a router which only routes and never runs
user space. You would starve it. Given it's somewhat obscure, but it's possible.

-Andi
-- 
ak@linux.intel.com -- Speaking for myself only

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