btrfs: defrag: don't waste CPU time on non-target extent

Changelog:
v2:
- Rebased to lastest misc-next
Just one small conflict with static_assert() update.
And this time only those patches are rebased to misc-next, thus it may cause conflicts with fixes for defrag_check_next_extent() in the future.

- Several grammar fixes

- Report accurate btrfs_defrag_ctrl::sectors_defragged This is inspired by a comment from Filipe that the skip check should be done in the defrag_collect_targets() call inside defrag_one_range().

This results a new patch in v2.

- Change the timing of btrfs_defrag_ctrl::last_scanned update Now it's updated inside defrag_one_range(), which will give us an accurate view, unlike the previous call site in defrag_one_cluster().

- Don't change the timing of extent threshold.

- Rename @last_target to @last_is_target in defrag_collect_targets()

v3:
- Add Reviewed-by tags

- Fix a wrong value in commit message of the 1st patch

- Make @orig_start const for the 3rd patch

- Fix a missing word "skip" in the 5th patch

- Remove one unnecessary assignment in the 5th patch As we don't return the defragged sectors to user space.

v4:
- Move the skip behavior before the btrfs_defrag_ctrl refactor So it can be backported to v5.16

- Slightly change how we use btrfs_defrag_ctrl::last_scanned Previously we use that value almost as range start, but that's not correct, as defrag_collect_targets() can update it before we do any defrag.

Now we pass explicit range start/len to defrag_one_cluster(), without re-using ctrl::last_scanned.

- Remove one incorrect range skip in defrag_one_cluster() There used to be a check against last_scanned to skip certain ranges. But that is not correct, as the last_scanned can already be larger than the first target after the 1st defrag_collect_targets() call.

Now last_scanned is only really utilized after one cluster is defragged.

This also removes the reviewed-by tag for the refactor patch

Qu Wenruo (5):
btrfs: defrag: allow defrag_one_cluster() to skip large extent which
is not a target
btrfs: uapi: introduce BTRFS_DEFRAG_RANGE_MASK for later sanity check
btrfs: defrag: introduce btrfs_defrag_ctrl structure for later usage
btrfs: defrag: use btrfs_defrag_ctrl to replace
btrfs_ioctl_defrag_range_args for btrfs_defrag_file()
btrfs: defrag: make btrfs_defrag_file() to report accurate number of
defragged sectors

 fs/btrfs/ctree.h           |  22 +++-
 fs/btrfs/file.c            |  21 ++--
 fs/btrfs/ioctl.c           | 200 ++++++++++++++++++++++---------------
 include/uapi/linux/btrfs.h |   6 +-
 4 files changed, 155 insertions(+), 94 deletions(-)

2.35.0