btrfs: Remove EXTENT_WRITEBACK

This flag was introduced in a52d9a80 ("Btrfs: Extent based page
cache code.") and subsequently it's usage effectively was removed by
1edbb734 ("Btrfs: reduce CPU usage in the extent_state tree") and
f2a97a9d ("btrfs: remove all unused functions"). Just remove it,
no functional changes.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -4229,8 +4229,7 @@ int try_release_extent_mapping(struct page *page, gfp_t mask)
 			}
 			if (!test_range_bit(tree, em->start,
 					    extent_map_end(em) - 1,
-					    EXTENT_LOCKED | EXTENT_WRITEBACK,
-					    0, NULL)) {
+					    EXTENT_LOCKED, 0, NULL)) {
 				set_bit(BTRFS_INODE_NEEDS_FULL_SYNC,
 					&btrfs_inode->runtime_flags);
 				remove_extent_mapping(map, em);

fs/btrfs/extent_io.h

@@ -9,22 +9,21 @@
 
 /* bits for the extent state */
 #define EXTENT_DIRTY		(1U << 0)
-#define EXTENT_WRITEBACK	(1U << 1)
-#define EXTENT_UPTODATE		(1U << 2)
-#define EXTENT_LOCKED		(1U << 3)
-#define EXTENT_NEW		(1U << 4)
-#define EXTENT_DELALLOC		(1U << 5)
-#define EXTENT_DEFRAG		(1U << 6)
-#define EXTENT_BOUNDARY		(1U << 9)
-#define EXTENT_NODATASUM	(1U << 10)
-#define EXTENT_CLEAR_META_RESV	(1U << 11)
-#define EXTENT_NEED_WAIT	(1U << 12)
-#define EXTENT_DAMAGED		(1U << 13)
-#define EXTENT_NORESERVE	(1U << 14)
-#define EXTENT_QGROUP_RESERVED	(1U << 15)
-#define EXTENT_CLEAR_DATA_RESV	(1U << 16)
-#define EXTENT_DELALLOC_NEW	(1U << 17)
-#define EXTENT_IOBITS		(EXTENT_LOCKED | EXTENT_WRITEBACK)
+#define EXTENT_UPTODATE		(1U << 1)
+#define EXTENT_LOCKED		(1U << 2)
+#define EXTENT_NEW		(1U << 3)
+#define EXTENT_DELALLOC		(1U << 4)
+#define EXTENT_DEFRAG		(1U << 5)
+#define EXTENT_BOUNDARY		(1U << 6)
+#define EXTENT_NODATASUM	(1U << 7)
+#define EXTENT_CLEAR_META_RESV	(1U << 8)
+#define EXTENT_NEED_WAIT	(1U << 9)
+#define EXTENT_DAMAGED		(1U << 10)
+#define EXTENT_NORESERVE	(1U << 11)
+#define EXTENT_QGROUP_RESERVED	(1U << 12)
+#define EXTENT_CLEAR_DATA_RESV	(1U << 13)
+#define EXTENT_DELALLOC_NEW	(1U << 14)
+#define EXTENT_IOBITS		(EXTENT_LOCKED)
 #define EXTENT_DO_ACCOUNTING    (EXTENT_CLEAR_META_RESV | \
 				 EXTENT_CLEAR_DATA_RESV)
 #define EXTENT_CTLBITS		(EXTENT_DO_ACCOUNTING)

include/trace/events/btrfs.h

@@ -102,7 +102,6 @@ TRACE_DEFINE_ENUM(COMMIT_TRANS);
 
 #define EXTENT_FLAGS						\
 	{ EXTENT_DIRTY,			"DIRTY"},		\
-	{ EXTENT_WRITEBACK,		"WRITEBACK"},		\
 	{ EXTENT_UPTODATE,		"UPTODATE"},		\
 	{ EXTENT_LOCKED,		"LOCKED"},		\
 	{ EXTENT_NEW,			"NEW"},			\