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

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Date:	Sun, 8 Apr 2007 19:02:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nigel Cunningham <ncunningham@...uxmail.org>
Subject: Re: [RFC][PATCH -mm] swsusp: Use rbtree for tracking allocated swap

On Sunday, 8 April 2007 14:56, Pavel Machek wrote:
> Hi!
> 
> > Some time ago we discussed the possibility of simplifying the swsusp's approach
> > towards tracking the swap pages allocated by it for saving the image (so that
> > they can be freed if there's an error).
> > 
> > I think we can get back to it now, as it is a nice optimization that should
> > allow us to use less memory (almost always) and improve performance a bit.
> > 
> 
> Well, I do not think you can measure the difference, but...

As far as the memory usage is concerned, I can. :-)  Usually, it takes 1 extent
(40 B on x86_64) to register all of the allocated swap pages.  If bitmaps are
used, we need as many bits as there are swap pages available (for 1 GB swap
and 4 KB pages that would be ~250000 bits, which gives ~8 pages, and we can
save more than 800 extents using that much memory).

> >  kernel/power/power.h  |   27 +---------
> >  kernel/power/swap.c   |   18 +-----
> >  kernel/power/swsusp.c |  135 ++++++++++++++++++++++++++------------------------
> >  kernel/power/user.c   |   22 +-------
> >  4 files changed, 85 insertions(+), 117 deletions(-)
> 
> ....as it removes code... I think we can do that. But it is 2.6.23+
> material.

Yes, I think so, but still we can ask Andrew to include it into -mm earlier? ;-)

Rafael
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