static inline struct page *compound_trans_head(struct page *page)
{
	if (PageTail(page)) {
		struct page *head;
		head = page->first_page;
		smp_rmb();
		/*
		 * head may be a dangling pointer.
		 * __split_huge_page_refcount clears PageTail before
		 * overwriting first_page, so if PageTail is still
		 * there it means the head pointer isn't dangling.
		 */
		if (PageTail(page))
			return head;
	}
	return page;
}
static inline struct page *compound_trans_head(struct page *page)
{
	if (PageTail(page)) {
		struct page *head;
		head = page->first_page;
		smp_rmb();
		 
		if (PageTail(page))
			return head;
	}
	return page;
}