linux-kernel - Re: [GIT PULL] RCU fix

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Message-ID: <20110531174430.GG2393@linux.vnet.ibm.com>
Date:	Tue, 31 May 2011 10:44:30 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] RCU fix

On Wed, Jun 01, 2011 at 02:05:21AM +0900, Linus Torvalds wrote:
> On Wed, Jun 1, 2011 at 1:27 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > Please pull the latest core-urgent-for-linus git tree from:
> >
> >   git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git core-urgent-for-linus
> 
> So remind me again why RCU switched to the stupid threads? It caused
> problems for rcutiny, it now causes silly problems for rcutree. Why do
> it? It's just extra complexity and no real advantage afaik.

The reason for the switch is to allow threads blocked in TREE_PREEMPT_RCU
and TINY_PREEMPT_RCU RCU read-side critical sections to have their
priority boosted in order to avoid OOM.  People have made these OOMs
happen, so this is not longer just a theoretical concern.

							Thanx, Paul
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