linux-kernel - Re: [Xen-devel] [PATCH RFC 3/4] xen-blkfront: prevent hoarding all grants

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Message-ID: <51DEC7C8.1090509@citrix.com>
Date:	Thu, 11 Jul 2013 16:57:12 +0200
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	<xen-devel@...ts.xen.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH RFC 3/4] xen-blkfront: prevent hoarding all
 grants

On 11/07/13 15:32, David Vrabel wrote:
> On 08/07/13 14:03, Roger Pau Monne wrote:
>> Prevent blkfront from hoarding all grants by adding a minimum number
>> of grants that must be free at all times. We still need a way to free
>> unused grants in blkfront, but this patch will mitigate the problem
>> in the meantime.
> 
> I think this could end up with the a frontend being able to get no
> grants because some other frontend always grabs the free grants first.
> 
> Particularly as the free grant callbacks are done in the wrong order.

I'm not so sure this patch is worth pushing any more, given that we will
be freeing grants instead of keeping them all in blkfront.

It seems like it might still be useful if we are under a lot of IO
pressure on different blkfronts and for example wanted to hot-attach a
new network interface (which requires 512 grants).
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