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

To: xfs@xxxxxxxxxxx
Subject: [PATCH 2/5] xfs: avoid repeated pointer dereferences
From: Alex Elder <aelder@xxxxxxx>
Date: Thu, 15 Apr 2010 13:17:30 -0500
Reply-to: aelder@xxxxxxx
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@xxxxxxx>

---
 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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