Re: [PATCH v3 0/5] xen/blk: persistent grant rework
From: Konrad Rzeszutek Wilk
Date: Mon Aug 27 2018 - 12:10:42 EST
On Fri, Aug 24, 2018 at 03:52:23PM +0200, Juergen Gross wrote:
> On 17/08/18 17:59, Roger Pau Monné wrote:
> > On Mon, Aug 13, 2018 at 04:01:09PM +0200, Juergen Gross wrote:
> >> Persistent grants are used in the Xen's blkfront/blkback drivers to
> >> avoid mapping/unmapping of I/O buffers in the backend for each I/O.
> >> While this speeds up processing quite a bit there are problems related
> >> to persistent grants in some configurations: domains with multiple
> >> block devices making use of persistent grants might suffer from a lack
> >> of grants if each of the block devices experienced a high I/O load at
> >> some time. This is due to the number of persistent grants per device
> >> only to be limited by a rather high maximum value, but never being
> >> released even in case of longer times without any I/O.
> >> This series modifies xen-blkback to unmap any domU page mapped via a
> >> persistent grant after a timeout (default: 60 seconds). The timeout
> >> is set to its default value again when a persistent grant has been
> >> used for an I/O.
> >> xen-blkfront is modified to scan every 10 seconds for persistent grants
> >> not in use by blkback any more and to remove such grants.
> >> The last 3 patches are small cleanups of blkfront and blkback drivers.
> >> V3:
> >> - patch 1: make timeout parameter static
> > Konrad if you are OK with this series, could you please send a pull
> > request to Jens?
Yes, let me do that now.