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 2 patches are small cleanups of blkfront and blkback drivers. Juergen Gross (4): xen/blkback: don't keep persistent grants too long xen/blkfront: cleanup stale persistent grants xen/blkfront: reorder tests in xlblk_init() xen/blkback: remove unused pers_gnts_lock from struct xen_blkif_ring drivers/block/xen-blkback/blkback.c | 77 +++++++++++++++--------- drivers/block/xen-blkback/common.h | 2 +- drivers/block/xen-blkfront.c | 115 ++++++++++++++++++++++++++++++++---- 3 files changed, 153 insertions(+), 41 deletions(-) -- 2.13.7
