The automatic block group removal patch introduced some regressions
in how discards are handled.
1/ FITRIM only iterates over block groups on disk - removed block groups
won't be trimmed.
2/ Clearing the dirty bit from extents in removed block groups means that
those extents won't be discarded when the block group is removed.
3/ More of a UI wart: We don't wait on block groups to be removed during
read-only remount or fs umount. This results in block groups that
/should/ have been discarded on thin provisioned storage hanging around
until the file system is mounted read-write again.
The following patches address these problems by:
1/ Iterating over block groups on disk and then iterating over free space.
This is consistent with how other file systems handle FITRIM.
2/ Putting removed block groups on a list so that they are automatically
discarded during btrfs_finish_extent_commit after transaction commit.
Note: This may still leave undiscarded space on disk if the system
crashes after transaction commit but before discard. The file system
itself will be compeltely consistent, but the user will need to trim
manually.
3/ Simple: We call btrfs_delete_unused_bgs explicitly during ro-remount
and umount.
4/ Skipping over blocks that contain superblocks during discard.
Changelog:
v1->v2
- -odiscard
- Fix ordering to ensure that we dont' discard extents freed in an
uncommitted transaction.
- FITRIM
- Don't start a transaction so the entire run is transactionless
- The loop can be interrupted while waiting on the chunk mutex and
after the discard has completed.
- The only lock held for the duration is the device_list_mutex. The
chunk mutex is take per loop iteration so normal operations should
continue while we're running, even on large file systems.
v2->v3
- -odiscard
- Factor out get/put block_group->trimming to ensure that cleanup always
happens at the last reference drop.
- Cleanup the free space cache on the last reference drop.
- Use list_move instead of list_add in case of multiple adds. We still
issue a warning but we shouldn't fall over.
- Explicitly delete unused block groups in close_ctree and ro-remount.
- FITRIM
- Cleaned up pointer tricks that abused &NULL->member.
- Take the commit_root_sem across loop iteration to protect against
transaction commit moving the commit root.
v3->v4
- skip superblocks during discard
Please apply.
Thanks,
-Jeff
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