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

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Date:	Tue, 24 Oct 2006 10:43:04 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Nigel Cunningham <ncunningham@...uxmail.org>
Cc:	Pavel Machek <pavel@....cz>, Andrew Morton <akpm@...l.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Use extents for recording what swap is allocated.

On Tuesday, 24 October 2006 01:04, Nigel Cunningham wrote:
> Hi.
> 
> On Mon, 2006-10-23 at 17:32 +0200, Pavel Machek wrote:
> > 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.
> > 
> > > This is also part of the ground work for implementing support for
> > > supporting multiple swap devices.
> > 
> > bitmaps were more efficient and longer than original code... I did not
> > _like_ them, but they are in now. I'd hate to change the code again,
> > for what, 0.5% gain?
> 
> 0.5% of what? This is part of what is needed to implement support for
> multiple swap devices. You could extend what you already have,
> implementing bitmaps that require a bit for every page of swap the user
> has swapon'd, but that doesn't seem efficient to me.

I agree.  Further, I though I would change the bitmaps thing at some point,
but there still are more urgent things to do. ;-)

> > ...and this is still longer than bitmaps.

Yes, it is.  Still I'd like to have a thorough look at it.  The idea is fine by me.

> > And SNAPSHOT_GET_SWAP_PAGE seems to support multiple swap spaces
> > already.
> 
> It may do, but swap.c certainly doesn't. It supports exactly one device.

That's correct.

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
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