btrfs: Simplify math in should_alloc chunk

Currently should_alloc_chunk uses ->total_bytes - ->bytes_readonly to
signify the total amount of bytes in this space info. However, given
Jeff's patch which adds bytes_pinned and bytes_may_use to the calculation
of num_allocated it becomes a lot more clear to just eliminate num_bytes
altogether and add the bytes_readonly to the amount of used space. That
way we don't change the results of the following statements. In the
process also start using btrfs_space_info_used.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -4418,8 +4418,7 @@ static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
 			      struct btrfs_space_info *sinfo, int force)
 {
 	struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
-	u64 num_bytes = sinfo->total_bytes - sinfo->bytes_readonly;
-	u64 num_allocated = sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned;
+	u64 bytes_used = btrfs_space_info_used(sinfo, false);
 	u64 thresh;
 
 	if (force == CHUNK_ALLOC_FORCE)
@@ -4431,7 +4430,7 @@ static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
 	 * global_rsv, it doesn't change except when the transaction commits.
 	 */
 	if (sinfo->flags & BTRFS_BLOCK_GROUP_METADATA)
-		num_allocated += calc_global_rsv_need_space(global_rsv);
+		bytes_used += calc_global_rsv_need_space(global_rsv);
 
 	/*
 	 * in limited mode, we want to have some free space up to
@@ -4441,11 +4440,11 @@ static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
 		thresh = btrfs_super_total_bytes(fs_info->super_copy);
 		thresh = max_t(u64, SZ_64M, div_factor_fine(thresh, 1));
 
-		if (num_bytes - num_allocated < thresh)
+		if (sinfo->total_bytes - bytes_used < thresh)
 			return 1;
 	}
 
-	if (num_allocated + SZ_2M < div_factor(num_bytes, 8))
+	if (bytes_used + SZ_2M < div_factor(sinfo->total_bytes, 8))
 		return 0;
 	return 1;
 }