linux-kernel - Re: [PATCH 1/3] Range tree implementation

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Message-ID: <4F96FE1D.8040906@linaro.org>
Date:	Tue, 24 Apr 2012 12:25:17 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Android Kernel Team <kernel-team@...roid.com>,
	Robert Love <rlove@...gle.com>, Mel Gorman <mel@....ul.ie>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Rik van Riel <riel@...hat.com>,
	Dmitry Adamushko <dmitry.adamushko@...il.com>,
	Dave Chinner <david@...morbit.com>, Neil Brown <neilb@...e.de>,
	Andrea Righi <andrea@...terlinux.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] Range tree implementation

On 04/24/2012 12:14 PM, Peter Zijlstra wrote:
> On Tue, 2012-04-24 at 10:49 -0700, John Stultz wrote:
>> This makes it
>> very difficult to provide generic list_head like behavior, as
>> the parent structures would need to be duplicated and removed,
>> and that has lots of memory ownership issues.
> You can in fact modify the rb-tree to have O(1) iteration by using the
> empty leaf pointers to keep pointers to next/prev nodes.
>
> Its a bit of a bother since you'd need to wrap ->rb_left and ->rb_right
> in functions.. but now that we have coccinelle that shouldn't actually
> be too hard.
>
Sorry, I'm not sure I'm following you.

My point above was that a generic range-tree implementation that manages 
the splitting and coalescing of ranges internally is difficult, due to 
memory ownership issues.  This makes it hard to have a generic list_head 
style structure that you can use in your own structures. Thus in a way 
similar to how the rb_tree leaves the insert and search implementation 
to the suers,  there is a range_tree_node structure, and the splitting 
and coalescing logic is left to the range-tree user.

Does your suggestion address the ownership issue differently?  Or is it 
just a general optimization improvement?

thanks
-john

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