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?

Thanks, Roger.