[PATCH v4 0/3] xen-blk(back|front): Let users disable persistent grants

[SeongJae Park <sjpark@amazon.com>]

From: SeongJae Park <sjpark@amazon.de>

Persistent grants feature provides high scalability.  On some small
systems, however, it could incur data copy overheads[1] and thus it is
required to be disabled.  But, there is no option to disable it.  For
the reason, this commit adds module parameters for disabling of the
feature.

[1] https://wiki.xen.org/wiki/Xen_4.3_Block_Protocol_Scalability

Baseline and Complete Git Trees
===============================

The patches are based on the v5.9-rc6.  You can also clone the complete
git tree:

    $ git clone git://github.com/sjp38/linux -b pgrants_disable_v4

The web is also available:
https://github.com/sjp38/linux/tree/pgrants_disable_v4

Patch History
=============

Changes from v3
(https://lore.kernel.org/xen-devel/20200922141549.26154-2-sjpark@amazon.com/)
- Remove unnecessary ternary operation (Jürgen Groß)
- Add 'Reviewed-by: Juergen Gross <jgross@suse.com>' and
  'Acked-by: Roger Pau Monné <roger.pau@citrix.com>'

Changes from v2
(https://lore.kernel.org/linux-block/20200922105209.5284-1-sjpark@amazon.com/)
- Avoid a race condition (Roger Pau Monné)

Because the option value is written twice, there could be a race if the
user change the value meanwhile.  This version fixes the problem by
reading the value once when each (front|back)end is created.

Changes from v1
(https://lore.kernel.org/linux-block/20200922070125.27251-1-sjpark@amazon.com/)
- use 'bool' parameter type (Jürgen Groß)
- Let blkfront can also disable the feature from its side
  (Roger Pau Monné)
- Avoid unnecessary xenbus_printf (Roger Pau Monné)
- Update frontend parameter doc


SeongJae Park (3):
  xen-blkback: add a parameter for disabling of persistent grants
  xen-blkfront: add a parameter for disabling of persistent grants
  xen-blkfront: Apply changed parameter name to the document

 .../ABI/testing/sysfs-driver-xen-blkback      |  9 ++++++++
 .../ABI/testing/sysfs-driver-xen-blkfront     | 11 +++++++++-
 drivers/block/xen-blkback/xenbus.c            | 22 ++++++++++++++-----
 drivers/block/xen-blkfront.c                  | 20 ++++++++++++-----
 4 files changed, 50 insertions(+), 12 deletions(-)

-- 
2.17.1