The upcoming NVMe ZNS Specification will define a new type of write command for zoned block devices, zone append. When when writing to a zoned block device using zone append, the start sector of the write is pointing at the start LBA of the zone to write to. Upon completion the block device will respond with the position the data has been placed in the zone. This from a high level perspective can be seen like a file system's block allocator, where the user writes to a file and the file-system takes care of the data placement on the device. In order to fully exploit the new zone append command in file-systems and other interfaces above the block layer, we choose to emulate zone append in SCSI and null_blk. This way we can have a single write path for both file-systems and other interfaces above the block-layer, like io_uring on zoned block devices, without having to care too much about the underlying characteristics of the device itself. The emulation works by providing a cache of each zone's write pointer, so zone append issued to the disk can be translated to a write with a starting LBA of the write pointer. This LBA is used as input zone number for the write pointer lookup in the zone write pointer offset cache and the cached offset is then added to the LBA to get the actual position to write the data. In SCSI we then turn the REQ_OP_ZONE_APPEND request into a WRITE(16) command. Upon successful completion of the WRITE(16), the cache will be updated to the new write pointer location and the written sector will be noted in the request. On error the cache entry will be marked as invalid and on the next write an update of the write pointer will be scheduled, before issuing the actual write. In order to reduce memory consumption, the only cached item is the offset of the write pointer from the start of the zone, everything else can be calculated. On an example drive with 52156 zones, the additional memory consumption of the cache is thus 52156 * 4 = 208624 Bytes or 51 4k Byte pages. The performance impact is neglectable for a spinning drive. For null_blk the emulation is way simpler, as null_blk's zoned block device emulation support already caches the write pointer position, so we only need to report the position back to the upper layers. Additional caching is not needed here. Furthermore we have converted zonefs to run use ZONE_APPEND for synchronous direct I/Os. Asynchronous I/O still uses the normal path via iomap. The series is based on v5.7-rc1 , but it should be trivial to re-base onto Jens' for-next branch once it re-opened. As Christoph asked for a branch I pushed it to a git repo at: git://git.kernel.org/pub/scm/linux/kernel/git/jth/linux.git zone-append.v6 https://git.kernel.org/pub/scm/linux/kernel/git/jth/linux.git/log/?h=zone-append.v6 Changes to v5: - Added patch to fix the memleak on failed scsi command setup - Added prep patch from Christoph for bio_add_hw_page - Added Christoph's suggestions for adding append pages to bios - Fixed compile warning with !CONFIG_BLK_DEV_ZONED - Damien re-worked revalidate zone - Added Christoph's suggestions for rescanning write pointers to update cache Changes to v4: - Added page merging for zone-append bios (Christoph) - Removed different locking schmes for zone management operations (Christoph) - Changed wp_ofst assignment from blk_revalidate_zones (Christoph) - Smaller nitpicks (Christoph) - Documented my changes to Keith's patch so it's clear where I messed up so he doesn't get blamed - Added Damien as a Co-developer to the sd emulation patch as he wrote as much code for it as I did (if not more) Changes since v3: - Remove impact of zone-append from bio_full() and bio_add_page() fast-path (Christoph) - All of the zone write pointer offset caching is handled in SCSI now (Christoph) - Drop null_blk pathces that damien sent separately (Christoph) - Use EXPORT_SYMBOL_GPL for new exports (Christoph) Changes since v2: - Remove iomap implementation and directly issue zone-appends from within zonefs (Christoph) - Drop already merged patch - Rebase onto new for-next branch Changes since v1: - Too much to mention, treat as a completely new series. block: Modify revalidate zones null_blk: Support REQ_OP_ZONE_APPEND Christoph Hellwig (1): block: rename __bio_add_pc_page to bio_add_hw_page Damien Le Moal (2): block: Modify revalidate zones null_blk: Support REQ_OP_ZONE_APPEND Johannes Thumshirn (7): scsi: free sgtables in case command setup fails block: provide fallbacks for blk_queue_zone_is_seq and blk_queue_zone_no block: introduce blk_req_zone_write_trylock scsi: sd_zbc: factor out sanity checks for zoned commands scsi: sd_zbc: emulate ZONE_APPEND commands block: export bio_release_pages and bio_iov_iter_get_pages zonefs: use REQ_OP_ZONE_APPEND for sync DIO Keith Busch (1): block: Introduce REQ_OP_ZONE_APPEND block/bio.c | 127 +++++++++--- block/blk-core.c | 52 +++++ block/blk-map.c | 5 +- block/blk-mq.c | 27 +++ block/blk-settings.c | 23 +++ block/blk-sysfs.c | 13 ++ block/blk-zoned.c | 22 +- block/blk.h | 4 +- drivers/block/null_blk_zoned.c | 39 +++- drivers/scsi/scsi_lib.c | 17 +- drivers/scsi/sd.c | 24 ++- drivers/scsi/sd.h | 43 +++- drivers/scsi/sd_zbc.c | 359 +++++++++++++++++++++++++++++++-- fs/zonefs/super.c | 80 +++++++- include/linux/blk_types.h | 14 ++ include/linux/blkdev.h | 25 ++- 16 files changed, 783 insertions(+), 91 deletions(-) -- 2.24.1
