xfs: return maximum free size from xfs_rtany_summary()

Instead of only returning whether there is any free space, return the
maximum size, which is fast thanks to the previous commit. This will be
used by two upcoming optimizations.
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_rtalloc.c

@@ -47,7 +47,7 @@ xfs_rtany_summary(
 	int			low,	/* low log2 extent size */
 	int			high,	/* high log2 extent size */
 	xfs_fileoff_t		bbno,	/* bitmap block number */
-	int			*stat)	/* out: any good extents here? */
+	int			*maxlog) /* out: max log2 extent size free */
 {
 	struct xfs_mount	*mp = args->mp;
 	int			error;
@@ -58,7 +58,7 @@ xfs_rtany_summary(
 	if (mp->m_rsum_cache) {
 		high = min(high, mp->m_rsum_cache[bbno] - 1);
 		if (low > high) {
-			*stat = 0;
+			*maxlog = -1;
 			return 0;
 		}
 	}
@@ -78,14 +78,14 @@ xfs_rtany_summary(
 		 * If there are any, return success.
 		 */
 		if (sum) {
-			*stat = 1;
+			*maxlog = log;
 			goto out;
 		}
 	}
 	/*
 	 * Found nothing, return failure.
 	 */
-	*stat = 0;
+	*maxlog = -1;
 out:
 	/* There were no extents at levels > log. */
 	if (mp->m_rsum_cache && log + 1 < mp->m_rsum_cache[bbno])
@@ -434,7 +434,7 @@ xfs_rtallocate_extent_near(
 	xfs_rtxnum_t		*rtx)	/* out: start rtext allocated */
 {
 	struct xfs_mount	*mp = args->mp;
-	int			any;	/* any useful extents from summary */
+	int			maxlog;	/* max useful extent from summary */
 	xfs_fileoff_t		bbno;	/* bitmap block number */
 	int			error;
 	int			i;	/* bitmap block offset (loop control) */
@@ -488,7 +488,7 @@ xfs_rtallocate_extent_near(
 		 * starting in this bitmap block.
 		 */
 		error = xfs_rtany_summary(args, log2len, mp->m_rsumlevels - 1,
-				bbno + i, &any);
+				bbno + i, &maxlog);
 		if (error) {
 			return error;
 		}
@@ -496,7 +496,7 @@ xfs_rtallocate_extent_near(
 		 * If there are any useful extents starting here, try
 		 * allocating one.
 		 */
-		if (any) {
+		if (maxlog >= 0) {
 			/*
 			 * On the positive side of the starting location.
 			 */
@@ -537,7 +537,7 @@ xfs_rtallocate_extent_near(
 					error = xfs_rtany_summary(args,
 							log2len,
 							mp->m_rsumlevels - 1,
-							bbno + j, &any);
+							bbno + j, &maxlog);
 					if (error) {
 						return error;
 					}
@@ -549,7 +549,7 @@ xfs_rtallocate_extent_near(
 					 * extent given, we've already tried
 					 * that allocation, don't do it again.
 					 */
-					if (any)
+					if (maxlog >= 0)
 						continue;
 					error = xfs_rtallocate_extent_block(args,
 							bbno + j, minlen,