linux-kernel - Re: [PATCH 1/5] [RFC] Add volatile range management code

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Message-ID: <CANN689HWYO5DD_p7yY39ethcFu_JO9hudMcDHd=K8FUfhpHZOg@mail.gmail.com>
Date:	Thu, 9 Aug 2012 02:46:37 -0700
From:	Michel Lespinasse <walken@...gle.com>
To:	John Stultz <john.stultz@...aro.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>,
	Mike Hommey <mh@...ndium.org>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Minchan Kim <minchan@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 1/5] [RFC] Add volatile range management code

On Fri, Jul 27, 2012 at 8:57 PM, John Stultz <john.stultz@...aro.org> wrote:
> v5:
> * Drop intervaltree for prio_tree usage per Michel &
>   Dmitry's suggestions.

Actually, I believe the ranges you need to track are non-overlapping, correct ?

If that is the case, a simple rbtree, sorted by start-of-range
address, would work best.
(I am trying to remove prio_tree users... :)

> +       /* First, find any existing intervals that overlap */
> +       prio_tree_iter_init(&iter, root, start, end);

Note that prio tree iterations take intervals as [start; last] not [start; end[
So if you want to stick with prio trees, you would have to use end-1 here.

> +       /* Coalesce left-adjacent ranges */
> +       prio_tree_iter_init(&iter, root, start-1, start);

Same here; you probably want to use start-1 on both ends

> +       node = prio_tree_next(&iter);
> +       while (node) {

I'm confused, I don't think you ever expect more than one range to
match, do you ???

> +       /* Coalesce right-adjacent ranges */
> +       prio_tree_iter_init(&iter, root, end, end+1);

Same again, here you probably want end on both ends

This is far from a complete code review, but I just wanted to point
out a couple details that jumped to me first. I am afraid I am missing
some of the background about how the feature is to be used to really
dig into the rest of the changes at this point :/

-- 
Michel "Walken" Lespinasse
A program is never fully debugged until the last user dies.
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