[PATCH 00/16] support non power of 2 zoned devices

Pankaj Raghav
2022-04-27T16:03:48Z

- 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, and so the po2 requirement
does not make sense for those type of zone storage devices.

Removing the po2 requirement from zone storage should therefore 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 [0].
Additional kernel stop-gap patches are provided in this series for dm-zoned.
Support for npo2 zonefs and btrfs support is addressed in this series.

There was an effort previously [1] to add support to non po2 devices via
device level emulation but that was rejected with a final conclusion
to add support for non po2 zoned device in the complete stack[2].

- Patchset description:
This patchset aims at adding support to non power of 2 zoned devices in
the block layer, nvme layer, null blk and adds support to btrfs and
zonefs.

This round of patches **will not** support f2fs and DM layer for non
power of 2 zoned devices. More about this in the future work section.

Patches 1-4 deals with removing the po2 constraint from the
block layer. Note that the patches have been split for clarity and it can
be squashed together if the community feels that is better.

Patches 5-6 deals with removing the constraint from nvme zns.

Patches 7-11 adds support to btrfs for non po2 zoned devices.

Patch 12 removes the po2 constraint in ZoneFS

Patch 13 removes the po2 contraint in null blk

Patches 14-16 adds conditions to not allow non power of 2 devices in
f2fs and DM.

- Performance:
PO2 zone sizes utilizes log and shifts instead of division when
determing alignment, zone number, etc. The same math cannot be used when
using a zoned device with non po2 zone size. Hence, to avoid any performance
regression on zoned devices with po2 zone sizes, the optimized math in the
hot paths has been retained with branching.

The performance was measured using null blk for regression
and the results have been posted in the appropriate commit log. No
performance regression was noticed.

- Testing
With respect to testing we need to tackle two things: one for regression
on po2 zoned device and progression on non po2 zoned devices.

kdevops (https://github.com/mcgrof/kdevops) was extensively used to
automate the testing for blktests and (x)fstests for btrfs changes. The
known failures were excluded during the test based on the baseline
v5.17.0-rc7

-- regression
Emulated zoned device with zone size =128M , nr_zones = 10000

Block and nvme zns:
blktests were run with no new failures

Btrfs:
Changes were tested with the following profile in QEMU:
[btrfs_simple_zns]
TEST_DIR=
SCRATCH_MNT=<mnt>
FSTYP=btrfs
MKFS_OPTIONS="-f -d single -m single"
TEST_DEV=<dev>
SCRATCH_DEV_POOL=<dev-pool>

No new failures were observed in btrfs, generic and shared test suite

ZoneFS:
zonefs-tests-nullblk.sh and zonefs-tests.sh from zonefs-tools were run
with no failures.

nullblk:
t/zbd/run-tests-against-nullb from fio was run with no failures.

F2FS and DM:
It was verified if f2fs and dm-zoned successfully mounts without any
error.

-- progression
Emulated zoned device with zone size = 96M , nr_zones = 10000

Block and nvme zns:
blktests were run with no new failures

Btrfs:
Same profile as po2 zone size was used.

Many tests in xfstests for btrfs included dm-flakey and some tests
required dm-linear. As they are not supported at the moment for non
po2 devices, those **tests were excluded for non po2 devices**.

No new failures were observed in btrfs, generic and shared test suite

ZoneFS:
zonefs-tests.sh from zonefs-tools were run with no failures.

nullblk:
A new section was added to cover non po2 devices:

section14()
{
conv_pcnt=10
zone_size=3
zone_capacity=3
max_open=${set_max_open}
zbd_test_opts+=("-o ${max_open}")
}
t/zbd/run-tests-against-nullb from fio was run with no failures.

F2FS and DM:
It was verified that f2fs and dm-zoned does not mount.

- Open issue:
* btrfs superblock location for zoned devices is expected to be in 0,
512GB(mirror) and 4TB(mirror) in the device. Zoned devices with po2
zone size will naturally align with these superblock location but non
po2 devices will not align with 512GB and 4TB offset.

The current approach for npo2 devices is to place the superblock mirror
zones near 512GB and 4TB that is **aligned to the zone size**. This
is of no issue for normal operation as we keep track where the superblock
mirror are placed but this can cause an issue with recovery tools for
zoned devices as they expect mirror superblock to be in 512GB and 4TB.

Note that ATM, recovery tools such as `btrfs check` does not work for
image dumps for zoned devices even for po2 zone sizes.

I hope this issue could be discussed as a part of the BoF on ZNS
during the upcoming LSFMM.

- Tools:
Some tools had to be updated to support non po2 devices. Once these
patches are accepted in the kernel, these tool updates will also be
upstreamed.
* btrfs-prog: https://github.com/Panky-codes/btrfs-progs/tree/remove-po2-btrfs
* blkzone: https://github.com/Panky-codes/util-linux/tree/remove-po2

- Future work
To reduce the amount of changes and testing, support for F2FS and DM was
excluded in this round of patches. The plan is to add support to them in
the forthcoming future.

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

Luis Chamberlain (4):
nvmet: use blk_queue_zone_no()
f2fs: call bdev_zone_sectors() only once on init_blkz_info()
f2fs: ensure only power of 2 zone sizes are allowed
dm-zoned: ensure only power of 2 zone sizes are allowed

Pankaj Raghav (12):
block: make blkdev_nr_zones and blk_queue_zone_no generic for npo2
zsze
block: add blk_queue_zone_aligned and bdev_zone_aligned helper
block: add bdev_zone_no helper
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
btrfs: zoned: Cache superblock location in btrfs_zoned_device_info
btrfs: zoned: add generic btrfs helpers for zoned devices
btrfs: zoned: Make sb_zone_number function non power of 2 compatible
btrfs: zoned: use btrfs zone helpers to support non po2 zoned devices
btrfs: zoned: relax the alignment constraint for zoned devices
zonefs: allow non power of 2 zoned devices
null_blk: allow non power of 2 zoned devices

block/blk-core.c | 3 +-
block/blk-zoned.c | 20 ++++--
drivers/block/null_blk/main.c | 4 +-
drivers/block/null_blk/zoned.c | 14 ++--
drivers/md/dm-zone.c | 12 ++++
drivers/nvme/host/zns.c | 11 +---
drivers/nvme/target/zns.c | 2 +-
fs/btrfs/volumes.c | 24 +++----
fs/btrfs/zoned.c | 115 +++++++++++++++++----------------
fs/btrfs/zoned.h | 41 ++++++++++--
fs/f2fs/super.c | 15 +++--
fs/zonefs/super.c | 6 +-
fs/zonefs/zonefs.h | 1 -
include/linux/blkdev.h | 48 +++++++++++++-
14 files changed, 208 insertions(+), 108 deletions(-)

--
2.25.1