linux-kernel - Re: [PATCH] Use extents for recording what swap is allocated.

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Date:	Tue, 24 Oct 2006 23:34:02 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Nigel Cunningham <ncunningham@...uxmail.org>,
	Andrew Morton <akpm@...l.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Use extents for recording what swap is allocated.

Hi!

> > Switch from bitmaps to using extents to record what swap is allocated;
> > they make more efficient use of memory, particularly where the allocated
> > storage is small and the swap space is large.
> 
> As I said before, I like the overall idea, but I have a bunch of
> comments.

Okay, if Rafael likes it... lets take a look.

First... what is the _worst case_ overhead? AFAICT extents are very
good at the best case, but tend to suck for the worst case...?

> > +#include <linux/suspend.h>
> > +#include "extent.h"
> > +
> > +/* suspend_get_extent
> > + *
> > + * Returns a free extent. May fail, returning NULL instead.
> > + */

Your comments are nice, and quite close to linuxdoc... Can we make
them proper linuxdoc?

> > +/* suspend_put_extent_chain.
> > + *
> > + * Frees a whole chain of extents.
> > + */
> > +void suspend_put_extent_chain(struct extent_chain *chain)
> 
> I'd call it suspend_free_all_extents().

This is actually important. As it does undocditional free(), it may
not be called "put".

> > +#ifndef EXTENT_H
> > +#define EXTENT_H
> > +
> > +struct extent {
> > +	unsigned long minimum, maximum;
> 
> Well, I'd use shorter names, but whatever.

Actually, minimum and 
	  maximum look too similar. start/end are really better names.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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