Provide simple functions to lazy migrate a process (or part thereof).
These will be used to implement memory migration for NUMA process
migration.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
 include/linux/mempolicy.h |    3 +++
 mm/mempolicy.c            |   40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -250,6 +250,9 @@ extern int vma_migratable(struct vm_area
 
 extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
 
+extern void lazy_migrate_vma(struct vm_area_struct *vma, int node);
+extern void lazy_migrate_process(struct mm_struct *mm, int node);
+
 #else
 
 struct mempolicy {};
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1173,6 +1173,46 @@ static long do_mbind(unsigned long start
 	return err;
 }
 
+void lazy_migrate_vma(struct vm_area_struct *vma, int node)
+{
+	nodemask_t nmask = nodemask_of_node(node);
+	LIST_HEAD(pagelist);
+
+	struct mempol_walk_data data = {
+		.nodes = &nmask,
+		.flags = MPOL_MF_MOVE | MPOL_MF_INVERT, /* move all pages not in set */
+		.private = &pagelist,
+		.vma = vma,
+	};
+
+	struct mm_walk walk = {
+		.pte_entry = check_pte_entry,
+		.mm = vma->vm_mm,
+		.private = &data,
+	};
+
+	if (vma->vm_file)
+		return;
+
+	if (!vma_migratable(vma))
+		return;
+
+	if (!walk_page_range(vma->vm_start, vma->vm_end, &walk))
+		migrate_pages_unmap_only(&pagelist);
+
+	putback_lru_pages(&pagelist);
+}
+
+void lazy_migrate_process(struct mm_struct *mm, int node)
+{
+	struct vm_area_struct *vma;
+
+	down_read(&mm->mmap_sem);
+	for (vma = mm->mmap; vma; vma = vma->vm_next)
+		lazy_migrate_vma(vma, node);
+	up_read(&mm->mmap_sem);
+}
+
 /*
  * User space interface with variable sized bitmaps for nodelists.
  */