Date: Thu, 23 Mar 2006 15:58:50 -0800
From: Andrew Morton <akpm@osdl.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: ncunningham@cyclades.com, linux-kernel@vger.kernel.org, pavel@suse.cz
Subject: Re: [PATCH] swsusp: separate swap-writing/reading code
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In-Reply-To: <200603232253.01025.rjw@sisk.pl>
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	<200603240713.41566.ncunningham@cyclades.com>
	<200603232253.01025.rjw@sisk.pl>
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"Rafael J. Wysocki" <rjw@sisk.pl> wrote:
>
> > I guess I missed this one somehow. Using a bitmap for allocated swap is really 
> > inefficient because the values are usually not fragmented much. Extents would 
> > have been a far better choice.
> 
> I agree it probably may be improved.  Still it seems to be good enough.  Further,
> it's more efficient than the previous solution, so I consider it as an improvement.
> Also this code has been tested for quite some time in -mm and appears to
> behave properly, at least we haven't got any bug reports related to it so far.

I think that temporarily allocating 1/32768th of total memory here is
reasonable, especially as it's not all allocated in a contiguous hunk.

> Currently I'm not working on any better solution.  If you can provide any
> patches to implement one, please submit them, but I think they'll have to be
> tested for as long as this code, in -mm.

I was a little saddened by the open-coded approach.  I'd expect that both
radix-trees and idr-trees could be used in this application.  Probably the
former.  (Radix-trees should have been designed from day one to store
`unsigned long's, not void*'s, so unless we change that, this application
will need to use typecasts when converting between void*'s and the stored
BITS_PER_LONG bitmaps).

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