mq-deadline: Improve support for zoned block devices

Hi Jens,

This patch series improves support for zoned block devices in the mq-deadline
scheduler by preserving the order of requeued writes (REQ_OP_WRITE*).

Please consider this patch series for the next merge window.

Thank you,

Bart.

Changes compared to v3:
- Addressed Christoph's review feedback.
- Dropped patch "block: Micro-optimize blk_req_needs_zone_write_lock()".
- Added three new patches:
  * block: Fix the type of the second bdev_op_is_zoned_write() argument
  * block: Introduce op_is_zoned_write()
  * block: mq-deadline: Reduce lock contention

Changes compared to v2:
- In the patch that micro-optimizes blk_req_needs_zone_write_lock(), inline
  bdev_op_is_zoned_write() instead of modifying it.
- In patch "block: Introduce blk_rq_is_seq_zoned_write()", converted "case
  REQ_OP_ZONE_APPEND" into a source code comment.
- Reworked deadline_skip_seq_writes() as suggested by Christoph.
- Dropped the patch that disabled head insertion for zoned writes.
- Dropped patch "mq-deadline: Fix a race condition related to zoned writes".
- Reworked handling of requeued requests: the 'next_rq' pointer has been
  removed and instead the position of the most recently dispatched request is
  tracked.
- Dropped the patches for tracking zone capacity and for restricting the number
  of active zones.

Changes compared to v1:
- Left out the patches related to request insertion and requeuing since
  Christoph is busy with reworking these patches.
- Added a patch for enforcing the active zone limit.

Bart Van Assche (11):
  block: Simplify blk_req_needs_zone_write_lock()
  block: Fix the type of the second bdev_op_is_zoned_write() argument
  block: Introduce op_is_zoned_write()
  block: Introduce blk_rq_is_seq_zoned_write()
  block: mq-deadline: Clean up deadline_check_fifo()
  block: mq-deadline: Simplify deadline_skip_seq_writes()
  block: mq-deadline: Improve deadline_skip_seq_writes()
  block: mq-deadline: Reduce lock contention
  block: mq-deadline: Track the dispatch position
  block: mq-deadline: Handle requeued requests correctly
  block: mq-deadline: Fix handling of at-head zoned writes

 block/blk-zoned.c      |  20 +++++---
 block/mq-deadline.c    | 114 +++++++++++++++++++++++++++++------------
 include/linux/blk-mq.h |   6 +++
 include/linux/blkdev.h |  13 +++--
 4 files changed, 107 insertions(+), 46 deletions(-)