zram: reduce load operation in page_same_filled

In page_same_filled function, all elements in the page is compared with
next index value.  The current comparison routine compares the (i)th and
(i+1)th values of the page.

In this case, two load operaions occur for each comparison.  But if we
store first value of the page stores at 'val' variable and using it to
compare with others, the load opearation is reduced.  It reduce load
operation per page by up to 64times.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Sangwoo Park <[email protected]>
Reviewed-by: Sergey Senozhatsky <[email protected]>
Acked-by: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 5 insertions, 3 deletions

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d303334e3da3..debee952dcc1 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -195,15 +195,17 @@ static bool page_same_filled(void *ptr, unsigned long *element)
 {
 	unsigned int pos;
 	unsigned long *page;
+	unsigned long val;
 
 	page = (unsigned long *)ptr;
+	val = page[0];
 
-	for (pos = 0; pos < PAGE_SIZE / sizeof(*page) - 1; pos++) {
-		if (page[pos] != page[pos + 1])
+	for (pos = 1; pos < PAGE_SIZE / sizeof(*page); pos++) {
+		if (val != page[pos])
 			return false;
 	}
 
-	*element = page[pos];
+	*element = val;
 
 	return true;
 }