ocfs2: give ocfs2 the ability to reclaim suballocator free bg

v4:

First of all, there is no code change in v4.

For patch [1/2]:
- Based on Joseph's v3 review comments:
  1. Modify the caller to initialize the ocfs2_read_hint_group_descriptor()
     input parameter '*released'.
  2. Rename the _reclaim_to_main_bm() to _ocfs2_reclaim_suballoc_to_main()
  3. Change the text "not empty rec" to "non empty rec"

- Revise the comments preceding the function _ocfs2_reclaim_suballoc_to_main().

- For the question: "How to distinguish the release case or a bug?"
  I write a comment before ocfs2_read_hint_group_descriptor().

- Revise the commit log to make it clearer.

For patch [2/2]:
- Revise the commit log to make it clearer.

Remove the v3 patch: "ocfs2: adjust spinlock_t ip_lock protection scope"
- Reason: This patch belongs to a different topic/job and should be
          handled separately.

v3:

For patch [1/3]:
- Factor out the reclaim code into a new function '_reclaim_to_main_bm'.
- The function ocfs2_read_hint_group_descriptor doesn't return -EIDRM
  when the group descriptor is invalid. The new code logic returns 0,
  and the input parameter '*released' is set to 1.

For patch [2/3]:
- Modify the code to follow the new logic of ocfs2_read_hint_group_descriptor
  as introduced in patch [1/3].

For patch [3/3]:
- No new changes.

v3 patch has passed the xfstests:
./check -g quick -T -b -s ocfs2 -e generic/032 -e generic/076 \
-e generic/081 -e generic/266 -e generic/272 -e generic/281 \
-e generic/331 -e generic/338 -e generic/347 -e generic/361 \
-e generic/479 -e generic/480 -e generic/628 -e generic/629 \
-e generic/648 -e generic/650

v2:

Create 2 new patches:
- ocfs2: detect released suballocator bg for fh_to_[dentry|parent]
- ocfs2: adjust spinlock_t ip_lock protection scope

In ocfs2_read_hint_group_descriptor()
- bypass the validation of GD when the BH is already managed by jbd2.

In _ocfs2_free_suballoc_bits()
- Move up the position of the vars 'idx' & 'rec'.
- Move up the position of the ocfs2_journal_dirty.
- Use le[16|32]_to_cpu() to access cl/fe/rec vars.
- Add error handling for calling ocfs2_extend_trans().
- adjust spin_lock ->ip_lock protection scope.
- Follow Glass's review comments, add 'comment' & 'else-break' for the
  'for-loop'.

v1:

Only create patch:
- ocfs2: give ocfs2 the ability to reclaim suballoc free bg

Heming Zhao (2):
  ocfs2: give ocfs2 the ability to reclaim suballoc free bg
  ocfs2: detect released suballocator BG for fh_to_[dentry|parent]

 fs/ocfs2/suballoc.c | 336 +++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 317 insertions(+), 19 deletions(-)

-- 
2.43.0