[PATCH 00/14] Improve I/O priority support

[Bart Van Assche <bvanassche@acm.org>]

Hi Jens,

A feature that is missing from the Linux kernel for storage devices that
support I/O priorities is to set the I/O priority in requests involving page
cache writeback. Since the identity of the process that triggers page cache
writeback is not known in the writeback code, the priority set by ioprio_set()
is ignored. However, an I/O cgroup is associated with writeback requests
by certain filesystems. Hence this patch series that implements the following
changes:
* Add an rq-qos policy that makes the I/O priority configurable per I/O cgroup
  and also that changes the I/O priority of requests to the lower of (request
  I/O priority, cgroup I/O priority).
* Introduce one queue per I/O priority in the mq-deadline scheduler.
* Dispatch the highest priority requests first.

Please consider this patch series for kernel v5.14.

Thanks,

Bart.

Changes compared to v1:
- Moved the code for assigning an I/O priority into a new rq-qos policy.
- Dropped patch "block/mq-deadline: Reduce the read expiry time for
  non-rotational media".
- Made sure that dd->async_depth >= 1.
- Implemented an aging mechanism such that lower priority requests are not
  postponed forever.

Bart Van Assche (14):
  block/Kconfig: Make the BLK_WBT and BLK_WBT_MQ entries consecutive
  block/blk-cgroup: Swap the blk_throtl_init() and blk_iolatency_init()
    calls
  block/blk-rq-qos: Move a function from a header file into a C file
  block: Introduce the ioprio rq-qos policy
  block/mq-deadline: Add several comments
  block/mq-deadline: Add two lockdep_assert_held() statements
  block/mq-deadline: Remove two local variables
  block/mq-deadline: Rename dd_init_queue() and dd_exit_queue()
  block/mq-deadline: Improve compile-time argument checking
  block/mq-deadline: Improve the sysfs show and store macros
  block/mq-deadline: Reserve 25% of scheduler tags for synchronous
    requests
  block/mq-deadline: Add I/O priority support
  block/mq-deadline: Add cgroup support
  block/mq-deadline: Prioritize high-priority requests

 Documentation/admin-guide/cgroup-v2.rst |   26 +
 block/Kconfig                           |   19 +-
 block/Kconfig.iosched                   |    6 +
 block/Makefile                          |    3 +
 block/blk-cgroup.c                      |   14 +-
 block/blk-ioprio.c                      |  236 +++++
 block/blk-ioprio.h                      |   19 +
 block/blk-rq-qos.c                      |   15 +
 block/blk-rq-qos.h                      |   14 +-
 block/mq-deadline-cgroup.c              |  185 ++++
 block/mq-deadline-cgroup.h              |  112 +++
 block/mq-deadline-main.c                | 1171 +++++++++++++++++++++++
 block/mq-deadline.c                     |  815 ----------------
 13 files changed, 1798 insertions(+), 837 deletions(-)
 create mode 100644 block/blk-ioprio.c
 create mode 100644 block/blk-ioprio.h
 create mode 100644 block/mq-deadline-cgroup.c
 create mode 100644 block/mq-deadline-cgroup.h
 create mode 100644 block/mq-deadline-main.c
 delete mode 100644 block/mq-deadline.c