RE: Add multi-page shared ring support to xen-blkfront/back

[Dan Magenheimer <dan.magenheimer@oracle.com>]

Haven't read the patch carefully, but a question:

Will blkback fall back safely to single-page allocation
if fragmentation has occurred... and, if so, will this inability
to allocate multi-page be dynamically propogated to blkfronts
(rather than just the largest ring size "supported" by
blkback)?

> -----Original Message-----
> From: Paul Durrant [mailto:paul.durrant@citrix.com]
> Sent: Tuesday, January 12, 2010 10:52 AM
> To: xen-devel@lists.xensource.com
> Subject: Re: [Xen-devel] Add multi-page shared ring support to
> xen-blkfront/back
> 
> 
> Paul Durrant wrote:
> > These patches add support for multi-page shared rings to 
> xen-blkfront/back.
> > Shared rings must always be a power of 2 in size and so the 
> size is controlled
> > by the new 'max_ring_page_order' module parameter of 
> xen-blkback. This defaults
> > to 0 so operationally there should be no difference with 
> these patches in place.
> > The maximum value of 'max_ring_page_order' is currently limited to 2
> > (i.e. 4 pages).
> > xen-blkfront will always use the largest shared ring size 
> supported by the back
> > end. To override this and continue to use a single page 
> ring, as before, set the
> > 'allow_multi_page_ring' module parameter to 0.
> > 
> 
> I don't know why git-send-email seems to have sent my patch 
> series into 
> a black hole. Here they are as attachments this time.
> 
>    Paul
> 
> -- 
> ===============================
> Paul Durrant, Software Engineer
> 
> Citrix Systems (R&D) Ltd.
> First Floor, Building 101
> Cambridge Science Park
> Milton Road
> Cambridge CB4 0FY
> United Kingdom
> ===============================
>