linux-kernel - [PATCH] zram: reduce load operation in page_same

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Date:   Thu, 2 Mar 2017 13:15:04 +0900
From:   Sangwoo <sangwoo2.park@....com>
To:     <minchan@...nel.org>, <ngupta@...are.org>
CC:     <sergey.senozhatsky.work@...il.com>,
        <linux-kernel@...r.kernel.org>, Sangwoo <sangwoo2.park@....com>
Subject: [PATCH] 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.

Signed-off-by: Sangwoo <sangwoo2.park@....com>
---
 drivers/block/zram/zram_drv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index e27d89a..87581d1 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -177,15 +177,17 @@ 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;
 }
-- 
2.6.2