linux-kernel - Re: [RFC][PATCH -mm] swsusp: Use rbtree for tracking allocated swap

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Date:	Sun, 08 Apr 2007 08:31:05 +1000
From:	Nigel Cunningham <ncunningham@...uxmail.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH -mm] swsusp: Use rbtree for tracking allocated swap

Hi.

On Sat, 2007-04-07 at 15:06 -0700, Andrew Morton wrote:
> On Sat, 7 Apr 2007 23:20:39 +0200 "Rafael J. Wysocki" <rjw@...k.pl> wrote:
> 
> > This should allow us to reduce the memory usage, practically always, and
> > improve performance.
> 
> And does it?

It will. I've been using extents for ages, for the same reasons. I don't
put them in an rb_tree because I view it as less than most efficient,
but it will still be a huge step forward from bitmaps in the normal
case.

The worst case would be if every second page of swap was in use, so that
you needed one extent per swap page. In that case, it would use more
memory than the bitmap, but far, far more common will be the case where
only one extent is needed for the whole swap partition, because the
algorithm used by the swap allocator minimises fragmentation.

Regards,

Nigel

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