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Re: [Xen-devel] Insane contiguous physical memory requirements in blkbk/

To: Aron Griffis <aron@xxxxxx>, "Stephen C. Tweedie" <sct@xxxxxxxxxx>
Subject: Re: [Xen-devel] Insane contiguous physical memory requirements in blkbk/blktap
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 05 Oct 2006 16:47:51 +0100
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On 5/10/06 16:38, "Aron Griffis" <aron@xxxxxx> wrote:

>> But is there any need at all for these pages to be contiguous?
> 
> I've been looking at the exact same question, but don't know the
> answer.  If you come up with a patch before I do, I'd be thrilled to
> test it.

This is easily fixable. Anywhere we use the virtual address to compute an
offset into a state structure, we can instead store the appropriate 'slot
index' in a spare field in the appropriate 'struct page'. That'll get rid of
any arithmetic on the virtual addresses that depends on them being
contiguous. Then the drivers can simply grab a bag of order-0 allocations.
That really only leaves the question of how much of this can be put in a
helper function (probably in balloon driver again) for use of all our
drivers.

 -- Keir



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