btrfs: better packing of btrfs_delayed_extent_op

btrfs_delayed_extent_op can be packed in a better way, it's 40 bytes now
and has 8 unused bytes. Reducing the level type to u8 makes it possible
to squeeze it to the padding byte after key. The bitfields were switched
to bool as there's space to store the full byte without increasing the
whole structure, besides that the generated assembly is smaller.

struct btrfs_delayed_extent_op {
	struct btrfs_disk_key      key;                  /*     0    17 */
	u8                         level;                /*    17     1 */
	bool                       update_key;           /*    18     1 */
	bool                       update_flags;         /*    19     1 */
	bool                       is_data;              /*    20     1 */

	/* XXX 3 bytes hole, try to pack */

	u64                        flags_to_set;         /*    24     8 */

	/* size: 32, cachelines: 1, members: 6 */
	/* sum members: 29, holes: 1, sum holes: 3 */
	/* last cacheline: 32 bytes */
};

The final size is 32 bytes which gives +26 object per slab page.

   text	   data	    bss	    dec	    hex	filename
 938811	  43670	  23144	1005625	  f5839	fs/btrfs/btrfs.ko.before
 938747	  43670	  23144	1005561	  f57f9	fs/btrfs/btrfs.ko.after
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/delayed-ref.c

@@ -493,12 +493,12 @@ update_existing_head_ref(struct btrfs_delayed_ref_root *delayed_refs,
 				memcpy(&existing_ref->extent_op->key,
 				       &ref->extent_op->key,
 				       sizeof(ref->extent_op->key));
-				existing_ref->extent_op->update_key = 1;
+				existing_ref->extent_op->update_key = true;
 			}
 			if (ref->extent_op->update_flags) {
 				existing_ref->extent_op->flags_to_set |=
 					ref->extent_op->flags_to_set;
-				existing_ref->extent_op->update_flags = 1;
+				existing_ref->extent_op->update_flags = true;
 			}
 			btrfs_free_delayed_extent_op(ref->extent_op);
 		}

fs/btrfs/delayed-ref.h

@@ -75,11 +75,11 @@ struct btrfs_delayed_ref_node {
 
 struct btrfs_delayed_extent_op {
 	struct btrfs_disk_key key;
+	u8 level;
+	bool update_key;
+	bool update_flags;
+	bool is_data;
 	u64 flags_to_set;
-	int level;
-	unsigned int update_key:1;
-	unsigned int update_flags:1;
-	unsigned int is_data:1;
 };
 
 /*

fs/btrfs/extent-tree.c

@@ -2988,9 +2988,9 @@ int btrfs_set_disk_extent_flags(struct btrfs_trans_handle *trans,
 		return -ENOMEM;
 
 	extent_op->flags_to_set = flags;
-	extent_op->update_flags = 1;
-	extent_op->update_key = 0;
-	extent_op->is_data = is_data ? 1 : 0;
+	extent_op->update_flags = true;
+	extent_op->update_key = false;
+	extent_op->is_data = is_data ? true : false;
 	extent_op->level = level;
 
 	ret = btrfs_add_delayed_extent_op(root->fs_info, trans, bytenr,
@@ -7980,12 +7980,9 @@ struct extent_buffer *btrfs_alloc_tree_block(struct btrfs_trans_handle *trans,
 		else
 			memset(&extent_op->key, 0, sizeof(extent_op->key));
 		extent_op->flags_to_set = flags;
-		if (skinny_metadata)
-			extent_op->update_key = 0;
-		else
-			extent_op->update_key = 1;
-		extent_op->update_flags = 1;
-		extent_op->is_data = 0;
+		extent_op->update_key = skinny_metadata ? false : true;
+		extent_op->update_flags = true;
+		extent_op->is_data = false;
 		extent_op->level = level;
 
 		ret = btrfs_add_delayed_tree_ref(root->fs_info, trans,