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

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Date:	Thu, 09 Aug 2012 12:11:51 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Michel Lespinasse <walken@...gle.com>
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 08/09/2012 02:46 AM, 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 ?
Correct.  Any overlapping range is coalesced.

> 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... :)

Sigh.  Sure.  Although I've blown with the wind on a number of different 
approaches for storing the ranges. I'm not particularly passionate about 
it, but the continual conflicting suggestions are a slight frustration.  :)


>> +       /* 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.
Thanks!  I think I hit this off-by-one issue in my testing, but fixed it 
on the backend  w/ :

     modify_range(&inode->i_data, start, end-1, &mark_nonvolatile_page);

Clearly fixing it at the start instead of papering over it is better.


>> +       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 ???

So yea.  If you already have two ranges (0-5),(10-15) and then add range 
(0-20) we need to coalesce the two existing ranges into the new one.


> 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 :/

Well, I really appreciate any feedback here.

thanks
-john

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