[3.8.y.z,extended,stable] Patch "mm: numa: avoid unnecessary disruption of NUMA hinting during" has been added to staging queue

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 1e9f627..270447e 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -94,10 +94,19 @@  static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 #endif /* CONFIG_MIGRATION */

 #ifdef CONFIG_NUMA_BALANCING
+extern bool pmd_trans_migrating(pmd_t pmd);
+extern void wait_migrate_huge_page(struct anon_vma *anon_vma, pmd_t *pmd);
 extern int migrate_misplaced_page(struct page *page, int node);
 extern int migrate_misplaced_page(struct page *page, int node);
 extern bool migrate_ratelimited(int node);
 #else
+static inline bool pmd_trans_migrating(pmd_t pmd)
+{
+	return false;
+}
+static inline void wait_migrate_huge_page(struct anon_vma *anon_vma, pmd_t *pmd)
+{
+}
 static inline int migrate_misplaced_page(struct page *page, int node)
 {
 	return -EAGAIN; /* can't migrate now */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a67726d..21ca328 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -908,6 +908,10 @@  int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		ret = 0;
 		goto out_unlock;
 	}
+
+	/* mmap_sem prevents this happening but warn if that changes */
+	WARN_ON(pmd_trans_migrating(pmd));
+
 	if (unlikely(pmd_trans_splitting(pmd))) {
 		/* split huge page running from under us */
 		spin_unlock(&src_mm->page_table_lock);
@@ -1313,6 +1317,17 @@  int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (unlikely(!pmd_same(pmd, *pmdp)))
 		goto out_unlock;

+	/*
+	 * If there are potential migrations, wait for completion and retry
+	 * without disrupting NUMA hinting information. Do not relock and
+	 * check_same as the page may no longer be mapped.
+	 */
+	if (unlikely(pmd_trans_migrating(*pmdp))) {
+		spin_unlock(&mm->page_table_lock);
+		wait_migrate_huge_page(vma->anon_vma, pmdp);
+		goto out;
+	}
+
 	page = pmd_page(pmd);
 	page_nid = page_to_nid(page);
 	count_vm_numa_event(NUMA_HINT_FAULTS);
@@ -1331,12 +1346,7 @@  int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 			goto clear_pmdnuma;
 	}

-	/*
-	 * If there are potential migrations, wait for completion and retry. We
-	 * do not relock and check_same as the page may no longer be mapped.
-	 * Furtermore, even if the page is currently misplaced, there is no
-	 * guarantee it is still misplaced after the migration completes.
-	 */
+	/* Migration could have started since the pmd_trans_migrating check */
 	if (!page_locked) {
 		spin_unlock(&mm->page_table_lock);
 		wait_on_page_locked(page);
diff --git a/mm/migrate.c b/mm/migrate.c
index 5a62622..8e117b7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1605,6 +1605,18 @@  int numamigrate_isolate_page(pg_data_t *pgdat, struct page *page)
 	return 1;
 }

+bool pmd_trans_migrating(pmd_t pmd)
+{
+	struct page *page = pmd_page(pmd);
+	return PageLocked(page);
+}
+
+void wait_migrate_huge_page(struct anon_vma *anon_vma, pmd_t *pmd)
+{
+	struct page *page = pmd_page(*pmd);
+	wait_on_page_locked(page);
+}
+
 /*
  * Attempt to migrate a misplaced page to the specified destination
  * node. Caller is expected to have an elevated reference count on