linux-kernel - Re: [RFC] [PATCH v5 0/3] fadvise: support POSIX_FADV

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Date:	Sun, 12 Feb 2012 12:58:34 +0100
From:	Andrea Righi <andrea@...terlinux.com>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [RFC] [PATCH v5 0/3] fadvise: support POSIX_FADV_NOREUSE

On Sun, Feb 12, 2012 at 03:16:07PM +0800, Hillf Danton wrote:
> Hello Andrea
> 
> On Sun, Feb 12, 2012 at 8:21 AM, Andrea Righi <andrea@...terlinux.com> wrote:
> [...]
> >  - Some of the routines to implement the generic interval tree has been taken
> >   from the x86 PAT code, that uses interval trees to keep track of PAT ranges
> >   (in the future it would be interesting to convert also the x86 PAT code to
> >   use the generic interval tree implementation).
> >
> Perhaps the tree implemented in this work could also be used in tracking
> regions in mm/hugetlb.c.
> 
> Thanks
> Hillf

Thanks, Hillf.

Yes, I quickly looked at the hugtlb code, it seems another potential
user of the interval tree. Now all the hugetlb regions are stored in a
list, the interval tree is a more efficient structure for lookups -
O(log(n)), so there are probably advantages in presence of many
different disjoint intervals.

mmh... at the moment there's not a way to map region_count() with the
current kinterval API, but we can easily extend it to provide also this
feature (count the overlap size of two intervals).

-Andrea
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