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

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Date:	Thu, 9 Aug 2012 21:39:21 +0200
From:	Andrea Righi <andrea@...terlinux.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Michel Lespinasse <walken@...gle.com>,
	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>,
	"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 Thu, Aug 09, 2012 at 12:33:17PM -0700, John Stultz wrote:
> On 08/09/2012 06:35 AM, Andrea Righi wrote:
> >On Thu, Aug 09, 2012 at 02:46:37AM -0700, Michel Lespinasse wrote:
> >>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... :)
> >>
> >John,
> >
> >JFYI, if you want to try a possible rbtree-based implementation, as
> >suggested by Michel you could try this one:
> >https://github.com/arighi/kinterval
> >
> >This implementation supports insertion, deletion and transparent merging
> >of adjacent ranges, as well as splitting ranges when chunks removed or
> >different chunk types are added in the middle of an existing range; so
> >if I'm not wrong probably you should be able to use this code as is,
> >without any modification.
> I do appreciate the suggestion, and considered this earlier when you
> posted this before.
> 
> Unfotunately the transparent merging/splitting/etc is actually not
> useful for me, since I manage other data per-range. The earlier
> generic rangetree/intervaltree implementations I tried limiting the
> interface to basically add(), remove(), search(), and search_next(),
> since when we coalesce intervals, we need to free the data in the
> structure referencing the interval being deleted (and similarly
> create new structures to reference new intervals created when we
> remove an interval). So the coalescing/splitting logic can't be
> pushed into the interval management code cleanly.
> 
> So while I might be able to make use of your kinterval in a fairly
> simple manner (only using add/del/lookup), I'm not sure it wins
> anything over just using an rbtree.  Especially since I'd have to do
> my own coalesce/splitting logic anyway, it would actually be more
> expensive as on add() it would still scan to check for overlapping
> ranges to merge.
> 
> I ended up dropping my generic intervaltree implementation because
> folks objected that it was so trivial (basically just wrapping an
> rbtree) and didn't handle some of the more complex intervaltree use
> cases (ie: allowing for overlapping intervals). The priotree seemed
> to match fairly closely the interface I was using, but apparently
> its on its way out as well, so unless anyone further objects, I
> think I'll just fall back to a simple rbtree implementation.

OK, everything makes sense now, thanks for the clarifications, and sorry
for suggesting yet another range/interval tree implementation. :)

I'll look at your patch set more in details and try to test/review it
closely.

-Andrea
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