On Fri, Aug 24, 2018 at 03:52:23PM +0200, Juergen Gross wrote:

On 17/08/18 17:59, Roger Pau Monn=E9 wrote:

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On Mon, Aug 13, 2018 at 04:01:09PM +0200, Juergen Gross wrote:

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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 relat=

ed

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to persistent grants in some configurations: domains with multiple
block devices making use of persistent grants might suffer from a la=

ck

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of grants if each of the block devices experienced a high I/O load a=

t

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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 gra=

nts

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not in use by blkback any more and to remove such grants.

The last 3 patches are small cleanups of blkfront and blkback driver=

s.

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V3:
- patch 1: make timeout parameter static

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Konrad if you are OK with this series, could you please send a pull
request to Jens?

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Ping?

Yes, let me do that now.

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Juergen