linux-kernel - Re: [mm][RFC][PATCH 0/11] mm accessor updates.

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Date:	Thu, 17 Dec 2009 06:45:51 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>, cl@...ux-foundation.org,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mingo@...e.hu" <mingo@...e.hu>, minchan.kim@...il.com
Subject: Re: [mm][RFC][PATCH 0/11] mm accessor updates.

On Thu, Dec 17, 2009 at 09:54:30AM +0100, Andi Kleen wrote:
> On Thu, Dec 17, 2009 at 09:45:34AM +0100, Peter Zijlstra wrote:
> > On Thu, 2009-12-17 at 09:40 +0100, Andi Kleen wrote:
> > > On Wed, Dec 16, 2009 at 11:57:04PM +0100, Peter Zijlstra wrote:
> > > > On Wed, 2009-12-16 at 19:31 +0900, KAMEZAWA Hiroyuki wrote:
> > > > 
> > > > > The problem of range locking is more than mmap_sem, anyway. I don't think
> > > > > it's possible easily.
> > > > 
> > > > We already have a natural range lock in the form of the split pte lock.
> > > > 
> > > > If we make the vma lookup speculative using RCU, we can use the pte lock
> > > 
> > > One problem is here that mmap_sem currently contains sleeps
> > > and RCU doesn't work for blocking operations until a custom
> > > quiescent period is defined.
> > 
> > Right, so one thing we could do is always have preemptible rcu present
> > in another RCU flavour, like
> > 
> > rcu_read_lock_sleep()
> > rcu_read_unlock_sleep()
> > call_rcu_sleep()
> > 
> > or whatever name that would be, and have PREEMPT_RCU=y only flip the
> > regular rcu implementation between the sched/sleep one.
> 
> That could work yes.

OK, I have to ask...

Why not just use the already-existing SRCU in this case?

							Thanx, Paul
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