staging: zcache: introduce zero-filled pages handler

Introduce zero-filled pages handler to capture and handle zero pages.
Acked-by: NDan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: NWanpeng Li <liwanp@linux.vnet.ibm.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/zcache/zcache-main.c

@@ -277,6 +277,33 @@ static void zcache_obj_free(struct tmem_obj *obj, struct tmem_pool *pool)
 	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 *p)
+{
+	void *user_mem;
+	struct page *page = (struct page *)p;
+
+	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,