btrfs: remove no longer used log_list member of struct btrfs_ordered_extent

The 'log_list' member of an ordered extent was used keep track of which
ordered extents we needed to wait after logging metadata, but is not used
anymore since commit 5636cf7d ("btrfs: remove the logged extents
infrastructure"), as we now always wait on ordered extent completion
before logging metadata. So just remove it since it's doing nothing and
making each ordered extent structure waste more memory (2 pointers).
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ordered-data.c

@@ -217,7 +217,6 @@ static int __btrfs_add_ordered_extent(struct inode *inode, u64 file_offset,
 	INIT_LIST_HEAD(&entry->root_extent_list);
 	INIT_LIST_HEAD(&entry->work_list);
 	init_completion(&entry->completion);
-	INIT_LIST_HEAD(&entry->log_list);
 	INIT_LIST_HEAD(&entry->trans_list);
 
 	trace_btrfs_ordered_extent_add(inode, entry);
@@ -449,7 +448,6 @@ void btrfs_put_ordered_extent(struct btrfs_ordered_extent *entry)
 	trace_btrfs_ordered_extent_put(entry->inode, entry);
 
 	if (refcount_dec_and_test(&entry->refs)) {
-		ASSERT(list_empty(&entry->log_list));
 		ASSERT(list_empty(&entry->trans_list));
 		ASSERT(list_empty(&entry->root_extent_list));
 		ASSERT(RB_EMPTY_NODE(&entry->rb_node));

fs/btrfs/ordered-data.h

@@ -104,9 +104,6 @@ struct btrfs_ordered_extent {
 	/* list of checksums for insertion when the extent io is done */
 	struct list_head list;
 
-	/* If we need to wait on this to be done */
-	struct list_head log_list;
-
 	/* If the transaction needs to wait on this ordered extent */
 	struct list_head trans_list;