thp: madvise(MADV_NOHUGEPAGE)

Add madvise MADV_NOHUGEPAGE to mark regions that are not important to be
hugepage backed.  Return -EINVAL if the vma is not of an anonymous type,
or the feature isn't built into the kernel.  Never silently return
success.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index 552f318..6b394f0 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -38,9 +38,10 @@
 static inline int khugepaged_enter(struct vm_area_struct *vma)
 {
 	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
-		if (khugepaged_always() ||
-		    (khugepaged_req_madv() &&
-		     vma->vm_flags & VM_HUGEPAGE))
+		if ((khugepaged_always() ||
+		     (khugepaged_req_madv() &&
+		      vma->vm_flags & VM_HUGEPAGE)) &&
+		    !(vma->vm_flags & VM_NOHUGEPAGE))
 			if (__khugepaged_enter(vma->vm_mm))
 				return -ENOMEM;
 	return 0;