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

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Message-ID: <20061025091022.GB7266@elf.ucw.cz>
Date:	Wed, 25 Oct 2006 11:10:22 +0200
From:	Pavel Machek <pavel@....cz>
To:	Nigel Cunningham <ncunningham@...uxmail.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Andrew Morton <akpm@...l.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Use extents for recording what swap is allocated.

Hi!

> > > > And now, can you do same computation assuming the swap allocator goes
> > > > completely crazy, and free space is in 1-page chunks?
> > > 
> > > The worst case is 3 * sizeof(unsigned long) *
> > > number_of_swap_extents_allocated bytes.
> > 
> > Okay, so if we got 4GB of swap space, thats 1MB swap pages, worst case
> > is you have one extent per page, on x86-64 that's 24MB. +kmalloc
> > overhead, I assume?
> 
> Sounds right.

Ok, 24-50MB per 4GB of swap space is not _that_ bad...

> > And you do linear walks over those extents, leading to O(n^2)
> > algorithm, no? That has bitten us before...
> 
> We start from where we last added an extent on the chain by default.

...but linear search through 24MB _is_ going to hurt.

> You're not going to respond to the other bit of my reply? I was
> beginning to think you were being more reasonable this time. Oh well.

Rafael likes your code, and that's a big plus, but do you have to
insult me?!
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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