[rfc][patch] mm: madvise(WILLNEED) for anonymous memory

[Peter Zijlstra <peterz@infradead.org>]

Hi,

Lennart asked for madvise(WILLNEED) to work on anonymous pages, he plans
to use this to pre-fault pages. He currently uses: mlock/munlock for
this purpose.

[ compile tested only ]

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
diff --git a/mm/madvise.c b/mm/madvise.c
index 93ee375..eff60ce 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -100,6 +100,24 @@ out:
 	return error;
 }
 
+static long madvice_willneed_anon(struct vm_area_struct *vma,
+				  struct vm_area_struct **prev,
+				  unsigned long start, unsigned long end)
+{
+	int ret, len;
+
+	*prev = vma;
+	if (end > vma->vm_end)
+		end = vma->vm_end;
+
+	len = end - start;
+	ret = get_user_pages(current, current->mm, start, len,
+			0, 0, NULL, NULL);
+	if (ret < 0)
+		return ret;
+	return ret == len ? 0 : -1;
+}
+
 /*
  * Schedule all required I/O operations.  Do not wait for completion.
  */
@@ -110,7 +128,7 @@ static long madvise_willneed(struct vm_area_struct * vma,
 	struct file *file = vma->vm_file;
 
 	if (!file)
-		return -EBADF;
+		return madvice_willneed_anon(vma, prev, start, end);
 
 	if (file->f_mapping->a_ops->get_xip_page) {
 		/* no bad return value, but ignore advice */