linux-kernel - Re: [Xen-devel] [PATCH] Persistent grant maps for xen blk drivers

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Date:	Fri, 21 Sep 2012 17:17:36 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Oliver Chick <oliver.chick@...rix.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>
Subject: Re: [Xen-devel] [PATCH] Persistent grant maps for xen blk drivers

On 21/09/12 15:27, Konrad Rzeszutek Wilk wrote:
> On Fri, Sep 21, 2012 at 01:23:48PM +0100, David Vrabel wrote:
>>
>> It's not just virtual space.  blkback in pvops kernels allocates its
>> pages from the balloon and if there aren't enough ballooned out pages it
>> has to allocate real pages (releasing the MFN back to Xen).
>>
>> Classic kernels didn't need to do this as there was an API for allocate
>> new "empty" struct page's that get mapped into kernel space.
> 
> Can we ressurect/implement that in the new pvops? We could use the memory
> hotplug mechanism to allocate "non-existent" memory. 

I don't see why not.  Provided the limitations are documented I wouldn't
make merging the persistent grant stuff dependent on it.

David
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