block: Introduce the ioprio rq-qos policy

Introduce an rq-qos policy that assigns an I/O priority to requests based
on blk-cgroup configuration settings. This policy has the following
advantages over the ioprio_set() system call:
- This policy is cgroup based so it has all the advantages of cgroups.
- While ioprio_set() does not affect page cache writeback I/O, this rq-qos
  controller affects page cache writeback I/O for filesystems that support
  assiociating a cgroup with writeback I/O. See also
  Documentation/admin-guide/cgroup-v2.rst.

Cc: Damien Le Moal <damien.lemoal@wdc.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Link: https://lore.kernel.org/r/20210618004456.7280-5-bvanassche@acm.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 9 insertions, 0 deletions

diff --git a/block/Kconfig b/block/Kconfig
index 6685578b2a20..e71c63eaaf52 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -162,6 +162,15 @@ config BLK_CGROUP_IOCOST
 	distributes IO capacity between different groups based on
 	their share of the overall weight distribution.
 
+config BLK_CGROUP_IOPRIO
+	bool "Cgroup I/O controller for assigning an I/O priority class"
+	depends on BLK_CGROUP
+	help
+	Enable the .prio interface for assigning an I/O priority class to
+	requests. The I/O priority class affects the order in which an I/O
+	scheduler and block devices process requests. Only some I/O schedulers
+	and some block devices support I/O priorities.
+
 config BLK_DEBUG_FS
 	bool "Block layer debugging information in debugfs"
 	default y