linux-kernel - Re: [RFC][PATCH 4/8] mm: RCU free vmas

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Message-ID: <20100105160502.GA8037@linux.vnet.ibm.com>
Date:	Tue, 5 Jan 2010 08:05:02 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	cl@...ux-foundation.org,
	"hugh.dickins" <hugh.dickins@...cali.co.uk>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [RFC][PATCH 4/8] mm: RCU free vmas

On Tue, Jan 05, 2010 at 09:28:36AM +0100, Peter Zijlstra wrote:
> On Mon, 2010-01-04 at 18:43 -0800, Paul E. McKenney wrote:
> > On Mon, Jan 04, 2010 at 07:24:33PM +0100, Peter Zijlstra wrote:
> > > TODO:
> > >  - should be SRCU, lack of call_srcu()
> > > 
> > > In order to allow speculative vma lookups, RCU free the struct
> > > vm_area_struct.
> > > 
> > > We use two means of detecting a vma is still valid:
> > >  - firstly, we set RB_CLEAR_NODE once we remove a vma from the tree.
> > >  - secondly, we check the vma sequence number.
> > > 
> > > These two things combined will guarantee that 1) the vma is still
> > > present and two, it still covers the same range from when we looked it
> > > up.
> > 
> > OK, I think I see what you are up to here.  I could get you a very crude
> > throw-away call_srcu() fairly quickly.  I don't yet have a good estimate
> > of how long it will take me to merge SRCU into the treercu infrastructure,
> > but am getting there.
> > 
> > So, which release are you thinking in terms of?
> 
> I'm not thinking any release yet, its very early and as Linus has
> pointed out, I seem to have forgotten a rather big piece of the
> picture :/
> 
> So I need to try and fix this glaring hole before we can continue.

OK, then I will think in terms of merging SRCU into treercu before
providing any sort of call_srcu().

							Thanx, Paul
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