page migration: Fail with error if swap not setup

[Christoph Lameter <clameter@sgi.com>]

Currently the migration of anonymous pages will silently fail if no swap 
is setup. This patch makes page migration functions check for available 
swap and fail with -ENODEV if no swap space is available.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.16-rc6/mm/mempolicy.c
===================================================================
--- linux-2.6.16-rc6.orig/mm/mempolicy.c	2006-03-14 16:31:15.000000000 -0800
+++ linux-2.6.16-rc6/mm/mempolicy.c	2006-03-14 17:25:09.000000000 -0800
@@ -330,9 +330,14 @@ check_range(struct mm_struct *mm, unsign
 	int err;
 	struct vm_area_struct *first, *vma, *prev;
 
-	/* Clear the LRU lists so pages can be isolated */
-	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL))
+	if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) {
+		/* Must have available swap entries for migration */
+		if (nr_swap_pages <=0)
+			return ERR_PTR(-ENODEV);
+
+		/* Clear the LRU lists so pages can be isolated */
 		lru_add_drain_all();
+	}
 
 	first = find_vma(mm, start);
 	if (!first)

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