On 12/12/19 11:09 PM, Naohiro Aota wrote:
To preserve sequential write pattern on the drives, we must serialize allocation and submit_bio. This commit add per-block group mutex "zone_io_lock" and find_free_extent_zoned() hold the lock. The lock is kept even after returning from find_free_extent(). It is released when submiting IOs corresponding to the allocation is completed. Implementing such behavior under __extent_writepage_io() is almost impossible because once pages are unlocked we are not sure when submiting IOs for an allocated region is finished or not. Instead, this commit add run_delalloc_hmzoned() to write out non-compressed data IOs at once using extent_write_locked_rage(). After the write, we can call btrfs_hmzoned_data_io_unlock() to unlock the block group for new allocation. Signed-off-by: Naohiro Aota <naohiro.aota@xxxxxxx>
Have you actually tested these patches with lock debugging on? The submit_compressed_extents stuff is async, so the unlocker owner will not be the lock owner, and that'll make all sorts of things blow up. This is just straight up broken.
I would really rather see a hmzoned block scheduler that just doesn't submit the bio's until they are aligned with the WP, that way this intellligence doesn't have to be dealt with at the file system layer. I get allocating in line with the WP, but this whole forcing us to allocate and submit the bio in lock step is just nuts, and broken in your subsequent patches. This whole approach needs to be reworked. Thanks,
Josef
