[PATCH 2/5] xfs: avoid repeated pointer dereferences

[PATCH 2/5] xfs: avoid repeated pointer dereferences

[Alex Elder]

In xlog_find_cycle_start() use a local variable for some repeated
operations rather than constantly accessing the memory location
whose address is passed in.

(This version drops an assertion that a pointer is non-null.)

Signed-off-by: Alex Elder <aelder@sgi.com>

---
 fs/xfs/xfs_log_recover.c |   25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

Index: b/fs/xfs/xfs_log_recover.c
===================================================================
--- a/fs/xfs/xfs_log_recover.c
+++ b/fs/xfs/xfs_log_recover.c
@@ -354,26 +354,27 @@ xlog_find_cycle_start(
 {
 	xfs_caddr_t	offset;
 	xfs_daddr_t	mid_blk;
+	xfs_daddr_t	end_blk;
 	uint		mid_cycle;
 	int		error;
 
-	mid_blk = BLK_AVG(first_blk, *last_blk);
-	while (mid_blk != first_blk && mid_blk != *last_blk) {
+	end_blk = *last_blk;
+	mid_blk = BLK_AVG(first_blk, end_blk);
+	while (mid_blk != first_blk && mid_blk != end_blk) {
 		error = xlog_bread(log, mid_blk, 1, bp, &offset);
 		if (error)
 			return error;
 		mid_cycle = xlog_get_cycle(offset);
-		if (mid_cycle == cycle) {
-			*last_blk = mid_blk;
-			/* last_half_cycle == mid_cycle */
-		} else {
-			first_blk = mid_blk;
-			/* first_half_cycle == mid_cycle */
-		}
-		mid_blk = BLK_AVG(first_blk, *last_blk);
+		if (mid_cycle == cycle)
+			end_blk = mid_blk;   /* last_half_cycle == mid_cycle */
+		else
+			first_blk = mid_blk; /* first_half_cycle == mid_cycle */
+		mid_blk = BLK_AVG(first_blk, end_blk);
 	}
-	ASSERT((mid_blk == first_blk && mid_blk+1 == *last_blk) ||
-	       (mid_blk == *last_blk && mid_blk-1 == first_blk));
+	ASSERT((mid_blk == first_blk && mid_blk+1 == end_blk) ||
+	       (mid_blk == end_blk && mid_blk-1 == first_blk));
+
+	*last_blk = end_blk;
 
 	return 0;
 }


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Re: [PATCH 2/5] xfs: avoid repeated pointer dereferences

[Christoph Hellwig]

On Thu, Apr 15, 2010 at 01:17:30PM -0500, Alex Elder wrote:
> In xlog_find_cycle_start() use a local variable for some repeated
> operations rather than constantly accessing the memory location
> whose address is passed in.
> 
> (This version drops an assertion that a pointer is non-null.)
> 
> Signed-off-by: Alex Elder <aelder@sgi.com>

I'm not entirely convinced about the need for this, but it at least
looks correct, so:

Reviewed-by: Christoph Hellwig <hch@lst.de>

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