[PATCH v8 00/11] support non power of 2 zoned device

[Pankaj Raghav]

- Background and Motivation:

The zone storage implementation in Linux, introduced since v4.10, first
targetted SMR drives which have a power of 2 (po2) zone size alignment
requirement. The po2 zone size was further imposed implicitly by the
block layer's blk_queue_chunk_sectors(), used to prevent IO merging
across chunks beyond the specified size, since v3.16 through commit
762380ad9322 ("block: add notion of a chunk size for request merging").
But this same general block layer po2 requirement for blk_queue_chunk_sectors()
was removed on v5.10 through commit 07d098e6bbad ("block: allow 'chunk_sectors'
to be non-power-of-2").

NAND, which is the media used in newer zoned storage devices, does not
naturally align to po2. In these devices, zone cap is not the same as the
po2 zone size. When the zone cap != zone size, then unmapped LBAs are
introduced to cover the space between the zone cap and zone size. po2
requirement does not make sense for these type of zone storage devices.
This patch series aims to remove these unmapped LBAs for zoned devices when
zone cap is npo2. This is done by relaxing the po2 zone size constraint
in the kernel and allowing zoned device with npo2 zone sizes if zone cap
== zone size.

Removing the po2 requirement from zone storage should be possible
now provided that no userspace regression and no performance regressions are
introduced. Stop-gap patches have been already merged into f2fs-tools to
proactively not allow npo2 zone sizes until proper support is added [1].

There were two efforts previously to add support to npo2 devices: 1) via
device level emulation [2] but that was rejected with a final conclusion
to add support for non po2 zoned device in the complete stack[3] 2)
adding support to the complete stack by removing the constraint in the
block layer and NVMe layer with support to btrfs, zonefs, etc which was
rejected with a conclusion to add a dm target for FS support [0]
to reduce the regression impact.

This series adds support to npo2 zoned devices in the block and nvme
layer and a new **dm target** is added: dm-po2z-target. This new
target will be initially used for filesystems such as btrfs and
f2fs that does not have native npo2 zone support.

- Patchset description:
Patches 1-2 deals with removing the po2 constraint from the
block layer.

Patches 3-4 deals with removing the constraint from nvme zns.

Patch 5 removes the po2 contraint in null blk

Patch 6 adds npo2 support to zonefs

Patches 7-11 adds support for npo2 zoned devices in the DM layer and
adds a new target dm-po2z-target which converts a npo2 zoned device into
a po2 zoned target.

The patch series is based on linux-next tag: next-20220727

Testing:
The new target was tested with blktest and zonefs test suite in qemu and
on a real ZNS device.

[0] https://lore.kernel.org/lkml/PH0PR04MB74166C87F694B150A5AE0F009BD09@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
[1] https://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs-tools.git/commit/?h=dev-test&id=6afcf6493578e77528abe65ab8b12f3e1c16749f
[2] https://lore.kernel.org/all/20220310094725.GA28499@xxxxxx/T/
[3] https://lore.kernel.org/all/20220315135245.eqf4tqngxxb7ymqa@unifi/

Changes since v1:
- Put the function declaration and its usage in the same commit (Bart)
- Remove bdev_zone_aligned function (Bart)
- Change the name from blk_queue_zone_aligned to blk_queue_is_zone_start
  (Damien)
- q is never null in from bdev_get_queue (Damien)
- Add condition during bringup and check for zsze == zcap for npo2
  drives (Damien)
- Rounddown operation should be made generic to work in 32 bits arch
  (bart)
- Add comments where generic calculation is directly used instead having
  special handling for po2 zone sizes (Hannes)
- Make the minimum zone size alignment requirement for btrfs to be 1M
  instead of BTRFS_STRIPE_LEN(David)

Changes since v2:
- Minor formatting changes

Changes since v3:
- Make superblock mirror align with the existing superblock log offsets
  (David)
- DM change return value and remove extra newline
- Optimize null blk zone index lookup with shift for po2 zone size

Changes since v4:
- Remove direct filesystems support for npo2 devices (Johannes, Hannes,
  Damien)

Changes since v5:
- Use DIV_ROUND_UP* helper instead of round_up as it breaks 32bit arch
  build in null blk(kernel-test-robot, Nathan)
- Use DIV_ROUND_UP_SECTOR_T also in blkdev_nr_zones function instead of
  open coding it with div64_u64
- Added extra condition in dm-zoned and in dm to reject non power of 2
  zone sizes.

Changes since v6:
- Added a new dm target for non power of 2 devices
- Added support for non power of 2 devices in the DM layer.

Changes since v7:
- Improved dm target for non power of 2 zoned devices with some bug
  fixes and rearrangement
- Removed some unnecessary comments.

Luis Chamberlain (1):
  dm-zoned: ensure only power of 2 zone sizes are allowed

Pankaj Raghav (10):
  block: make bdev_nr_zones and disk_zone_no generic for npo2 zsze
  block: allow blk-zoned devices to have non-power-of-2 zone size
  nvme: zns: Allow ZNS drives that have non-power_of_2 zone size
  nvmet: Allow ZNS target to support non-power_of_2 zone sizes
  null_blk: allow non power of 2 zoned devices
  zonefs: allow non power of 2 zoned devices
  dm-zone: use generic helpers to calculate offset from zone start
  dm-table: allow non po2 zoned devices
  dm: call dm_zone_endio after the target endio callback for zoned
    devices
  dm: add power-of-2 zoned target for non-power-of-2 zoned devices

 block/blk-core.c                  |   2 +-
 block/blk-zoned.c                 |  37 +++--
 drivers/block/null_blk/main.c     |   5 +-
 drivers/block/null_blk/null_blk.h |   6 +
 drivers/block/null_blk/zoned.c    |  18 ++-
 drivers/md/Kconfig                |   9 ++
 drivers/md/Makefile               |   2 +
 drivers/md/dm-po2z-target.c       | 261 ++++++++++++++++++++++++++++++
 drivers/md/dm-table.c             |  21 ++-
 drivers/md/dm-zone.c              |  10 +-
 drivers/md/dm-zoned-target.c      |   8 +
 drivers/md/dm.c                   |   8 +-
 drivers/nvme/host/zns.c           |  16 +-
 drivers/nvme/target/zns.c         |   3 +-
 fs/zonefs/super.c                 |   6 +-
 fs/zonefs/zonefs.h                |   1 -
 include/linux/blkdev.h            |  91 ++++++++---
 include/linux/device-mapper.h     |   9 ++
 18 files changed, 438 insertions(+), 75 deletions(-)
 create mode 100644 drivers/md/dm-po2z-target.c

-- 
2.25.1