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Subject: Re: [RFC][PATCH 4/8] mm: RCU free vmas
From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@linux.vnet.ibm.com
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
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Date: Tue, 05 Jan 2010 09:28:36 +0100
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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.