UPSTREAM: 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/1488428104-7257-1-git-send-email-sangwoo2.park@lge.com
Signed-off-by: Sangwoo Park <sangwoo2.park@lge.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit f0fe9984656604ea8effd5ff82709ff8ce1f954b)
Signed-off-by: Peter Kalauskas <peskal@google.com>
Bug: 112488418
Change-Id: I6b58b583e83139eee9f0540da12850c43510cb8e

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 2dbd397812547dcc807c195df0a2e9ceafdf7eef..2db2459857fbbbc3ce7218ee11d5c64b4d6515c5 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -194,15 +194,17 @@ 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;
 }