--- linux-2.6.20.x86_64/mm/madvise.c.madv_free	2007-04-19 16:46:22.000000000 -0400
+++ linux-2.6.20.x86_64/mm/madvise.c	2007-04-19 16:52:19.000000000 -0400
@@ -130,7 +130,8 @@ static long madvise_willneed(struct vm_a
  */
 static long madvise_dontneed(struct vm_area_struct * vma,
 			     struct vm_area_struct ** prev,
-			     unsigned long start, unsigned long end)
+			     unsigned long start, unsigned long end,
+			     int behavior)
 {
 	*prev = vma;
 	if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
@@ -142,12 +143,14 @@ static long madvise_dontneed(struct vm_a
 			.last_index = ULONG_MAX,
 		};
 		zap_page_range(vma, start, end - start, &details);
-	} else {
+	} else if (behavior == MADV_FREE) {
 		struct zap_details details = {
 			.madv_free = 1,
 		};
 		zap_page_range(vma, start, end - start, &details);
-	}
+	} else /* behavior == MADV_DONTNEED */
+		zap_page_range(vma, start, end - start, NULL);
+
 	return 0;
 }
 
@@ -219,10 +222,9 @@ madvise_vma(struct vm_area_struct *vma, 
 		error = madvise_willneed(vma, prev, start, end);
 		break;
 
-	/* FIXME: POSIX says that MADV_DONTNEED cannot throw away data. */
 	case MADV_DONTNEED:
 	case MADV_FREE:
-		error = madvise_dontneed(vma, prev, start, end);
+		error = madvise_dontneed(vma, prev, start, end, behavior);
 		break;
 
 	default: