staging: zcache: introduce zero filled pages handler

Introduce zero-filled pages handler to capture and handle zero pages.

Acked-by: Dan Magenheimer <[e-mail]>
Signed-off-by: Wanpeng Li <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/zcache/zcache-main.c

···
 	kmem_cache_free(zcache_obj_cache, obj);
 }
 
+static bool page_is_zero_filled(void *ptr)
+{
+	unsigned int pos;
+	unsigned long *page;
+
+	page = (unsigned long *)ptr;
+
+	for (pos = 0; pos < PAGE_SIZE / sizeof(*page); pos++) {
+		if (page[pos])
+			return false;
+	}
+
+	return true;
+}
+
+static void handle_zero_filled_page(void *page)
+{
+	void *user_mem;
+
+	user_mem = kmap_atomic(page);
+	memset(user_mem, 0, PAGE_SIZE);
+	kunmap_atomic(user_mem);
+
+	flush_dcache_page(page);
+}
+
 static struct tmem_hostops zcache_hostops = {
 	.obj_alloc = zcache_obj_alloc,
 	.obj_free = zcache_obj_free,