zram: count same page write as page_stored

Regardless of whether it is same page or not, it's surely write and
stored to zram so we should increase pages_stored stat.  Otherwise, user
can see zero value via mm_stats although he writes a lot of pages to
zram.

Link: http://lkml.kernel.org/r/1494834068-27004-1-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -469,6 +469,7 @@ static bool zram_same_page_write(struct zram *zram, u32 index,
 		zram_slot_unlock(zram, index);
 
 		atomic64_inc(&zram->stats.same_pages);
+		atomic64_inc(&zram->stats.pages_stored);
 		return true;
 	}
 	kunmap_atomic(mem);
@@ -524,6 +525,7 @@ static void zram_free_page(struct zram *zram, size_t index)
 		zram_clear_flag(zram, index, ZRAM_SAME);
 		zram_set_element(zram, index, 0);
 		atomic64_dec(&zram->stats.same_pages);
+		atomic64_dec(&zram->stats.pages_stored);
 		return;
 	}