mm: hugetlb: bail out unmapping after serving reference page

When unmapping a given VM range, we could bail out if a reference page is
supplied and is unmapped, which is a minor optimization.
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -2280,6 +2280,10 @@ void __unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start,
 		if (pte_dirty(pte))
 			set_page_dirty(page);
 		list_add(&page->lru, &page_list);
+
+		/* Bail out after unmapping reference page if supplied */
+		if (ref_page)
+			break;
 	}
 	flush_tlb_range(vma, start, end);
 	spin_unlock(&mm->page_table_lock);