xfs: speed up xfs_iwalk_adjust_start a little bit

Replace the open-coded loop that recomputes freecount with a single call
to a bit weight function.
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/xfs_iwalk.c

@@ -22,6 +22,7 @@
 #include "xfs_trans.h"
 #include "xfs_pwork.h"
 #include "xfs_ag.h"
+#include "xfs_bit.h"
 
 /*
  * Walking Inodes in the Filesystem
@@ -131,21 +132,11 @@ xfs_iwalk_adjust_start(
 	struct xfs_inobt_rec_incore	*irec)	/* btree record */
 {
 	int				idx;	/* index into inode chunk */
-	int				i;
 
 	idx = agino - irec->ir_startino;
 
-	/*
-	 * We got a right chunk with some left inodes allocated at it.  Grab
-	 * the chunk record.  Mark all the uninteresting inodes free because
-	 * they're before our start point.
-	 */
-	for (i = 0; i < idx; i++) {
-		if (XFS_INOBT_MASK(i) & ~irec->ir_free)
-			irec->ir_freecount++;
-	}
-
 	irec->ir_free |= xfs_inobt_maskn(0, idx);
+	irec->ir_freecount = hweight64(irec->ir_free);
 }
 
 /* Allocate memory for a walk. */