btrfs: don't hold an extra reference for redirtied buffers

When btrfs_redirty_list_add redirties a buffer, it also acquires
an extra reference that is released on transaction commit.  But
this is not required as buffers that are dirty or under writeback
are never freed (look for calls to extent_buffer_under_io())).

Remove the extra reference and the infrastructure used to drop it
again.

History behind redirty logic:

In the first place, it used releasing_list to hold all the
to-be-released extent buffers, and decided which buffers to re-dirty at
the commit time. Then, in a later version, the behaviour got changed to
re-dirty a necessary buffer and add re-dirtied one to the list in
btrfs_free_tree_block(). In short, the list was there mostly for the
patch series' historical reason.

Reviewed-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
[ add Naohiro's comment regarding history ]
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 4 insertions, 24 deletions

diff --git a/fs/btrfs/zoned.c b/fs/btrfs/zoned.c
index dac879fe2871..bda301a55cbe 100644
--- a/fs/btrfs/zoned.c
+++ b/fs/btrfs/zoned.c
@@ -1602,37 +1602,17 @@ void btrfs_calc_zone_unusable(struct btrfs_block_group *cache)
 void btrfs_redirty_list_add(struct btrfs_transaction *trans,
 			    struct extent_buffer *eb)
 {
-	struct btrfs_fs_info *fs_info = eb->fs_info;
-
-	if (!btrfs_is_zoned(fs_info) ||
-	    btrfs_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN) ||
-	    !list_empty(&eb->release_list))
+	if (!btrfs_is_zoned(eb->fs_info) ||
+	    btrfs_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN))
 		return;
 
+	ASSERT(!test_bit(EXTENT_BUFFER_DIRTY, &eb->bflags));
+
 	memzero_extent_buffer(eb, 0, eb->len);
 	set_bit(EXTENT_BUFFER_NO_CHECK, &eb->bflags);
 	set_extent_buffer_dirty(eb);
 	set_extent_bits_nowait(&trans->dirty_pages, eb->start,
 			       eb->start + eb->len - 1, EXTENT_DIRTY);
-
-	spin_lock(&trans->releasing_ebs_lock);
-	list_add_tail(&eb->release_list, &trans->releasing_ebs);
-	spin_unlock(&trans->releasing_ebs_lock);
-	atomic_inc(&eb->refs);
-}
-
-void btrfs_free_redirty_list(struct btrfs_transaction *trans)
-{
-	spin_lock(&trans->releasing_ebs_lock);
-	while (!list_empty(&trans->releasing_ebs)) {
-		struct extent_buffer *eb;
-
-		eb = list_first_entry(&trans->releasing_ebs,
-				      struct extent_buffer, release_list);
-		list_del_init(&eb->release_list);
-		free_extent_buffer(eb);
-	}
-	spin_unlock(&trans->releasing_ebs_lock);
 }
 
 bool btrfs_use_zone_append(struct btrfs_bio *bbio)