Date: Mon, 28 Dec 2009 06:27:46 +0530
From: Balbir Singh <balbir@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
       "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "linux-mm@kvack.org" <linux-mm@kvack.org>,
       "minchan.kim@gmail.com" <minchan.kim@gmail.com>,
       cl@linux-foundation.org
Subject: Re: [RFC PATCH] asynchronous page fault.
Message-ID: <20091228005746.GE3601@balbir.in.ibm.com>
Reply-To: balbir@linux.vnet.ibm.com
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* Peter Zijlstra <peterz@infradead.org> [2009-12-27 12:19:56]:

> Your changelog states as much.
> 
> "Even if RB-tree rotation occurs while we walk tree for look-up, we just
> miss vma without oops."
> 
> However, since this is the case, do we still need the
> rcu_assign_pointer() conversion your patch does? All I can see it do is
> slow down all RB-tree users, without any gain.

Don't we need the rcu_assign_pointer() on the read side primarily to
make sure the pointer is still valid and assignments (writes) are not
re-ordered? Are you suggesting that the pointer assignment paths be
completely atomic?

-- 
	Balbir
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