+#ifdef CONFIG_MIGRATION
+/*
+ * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
+ * Called by migrate.c to remove migration ptes, but might be used more later.
+ */
+static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
+ struct vm_area_struct *, unsigned long, void *), void *arg)
+{
+ struct anon_vma *anon_vma;
+ struct anon_vma_chain *avc;
+ int ret = SWAP_AGAIN;
+
+ /*
+ * Note: remove_migration_ptes() cannot use page_lock_anon_vma()
+ * because that depends on page_mapped(); but not all its usages
+ * are holding mmap_sem. Users without mmap_sem are required to
+ * take a reference count to prevent the anon_vma disappearing
+ */
+ anon_vma = page_anon_vma(page);
+ if (!anon_vma)
+ return ret;
+ spin_lock(&anon_vma->lock);
+ list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
+ struct vm_area_struct *vma = avc->vma;
+ unsigned long address = vma_address(page, vma);
+ if (address == -EFAULT)
+ continue;
+ ret = rmap_one(page, vma, address, arg);
+ if (ret != SWAP_AGAIN)
+ break;
+ }
+ spin_unlock(&anon_vma->lock);
+ return ret;
+}
+
+static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
+ struct vm_area_struct *, unsigned long, void *), void *arg)
+{
+ struct address_space *mapping = page->mapping;
+ pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
+ struct vm_area_struct *vma;
+ struct prio_tree_iter iter;
+ int ret = SWAP_AGAIN;
+
+ if (!mapping)
+ return ret;
+ spin_lock(&mapping->i_mmap_lock);
+ vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
+ unsigned long address = vma_address(page, vma);
+ if (address == -EFAULT)
+ continue;
+ ret = rmap_one(page, vma, address, arg);
+ if (ret != SWAP_AGAIN)
+ break;
+ }
+ /*
+ * No nonlinear handling: being always shared, nonlinear vmas
+ * never contain migration ptes. Decide what to do about this
+ * limitation to linear when we need rmap_walk() on nonlinear.
+ */
+ spin_unlock(&mapping->i_mmap_lock);
+ return ret;
+}
+
+int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
+ struct vm_area_struct *, unsigned long, void *), void *arg)
+{
+ VM_BUG_ON(!PageLocked(page));
+
+ if (unlikely(PageKsm(page)))
+ return rmap_walk_ksm(page, rmap_one, arg);
+ else if (PageAnon(page))
+ return rmap_walk_anon(page, rmap_one, arg);
+ else
+ return rmap_walk_file(page, rmap_one, arg);
+}
+#endif /* CONFIG_MIGRATION */