[PATCH] buffer: a small optimization in grow_buffers

[Mikulas Patocka <mpatocka@xxxxxxxxxx>]

This patch replaces a loop with a "tzcnt" instruction.

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -1020,11 +1020,7 @@ grow_buffers(struct block_device *bdev,
 	pgoff_t index;
 	int sizebits;
 
-	sizebits = -1;
-	do {
-		sizebits++;
-	} while ((size << sizebits) < PAGE_SIZE);
-
+	sizebits = PAGE_SHIFT - __ffs(size);
 	index = block >> sizebits;
 
 	/*