[PATCH v3 3/5] hugetlb: only set HPageMigratable for migratable hstates

[Mike Kravetz]

The HP_Migratable flag indicates a page is a candidate for migration.
Only set the flag if the page's hstate supports migration.  This allows
the migration paths to detect non-migratable pages earlier.  If migration
is not supported for the hstate, HP_Migratable will not be set, the page
will not be isolated and no attempt will be made to migrate.  We should
never get to unmap_and_move_huge_page for a page where migration is not
supported, so throw a warning if we do.

Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 fs/hugetlbfs/inode.c    | 2 +-
 include/linux/hugetlb.h | 9 +++++++++
 mm/hugetlb.c            | 8 ++++----
 mm/migrate.c            | 9 ++++-----
 4 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index e1d7ed2a53a9..93f7b8d3c5fd 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -735,7 +735,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
 
 		mutex_unlock(&hugetlb_fault_mutex_table[hash]);
 
-		SetHPageMigratable(page);
+		SetHPageMigratableIfSupported(page);
 		/*
 		 * unlock_page because locked by add_to_page_cache()
 		 * put_page() due to reference from alloc_huge_page()
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 58be44a915d1..cd1960541f2a 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -740,6 +740,15 @@ static inline bool hugepage_migration_supported(struct hstate *h)
 	return arch_hugetlb_migration_supported(h);
 }
 
+/*
+ * Only set HPageMigratable if migration supported for page
+ */
+static inline void SetHPageMigratableIfSupported(struct page *page)
+{
+	if (hugepage_migration_supported(page_hstate(page)))
+		SetHPageMigratable(page);
+}
+
 /*
  * Movability check is different as compared to migration check.
  * It determines whether or not a huge page should be placed on
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index f1a3c8230dbf..4da1a29ac5e2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4194,7 +4194,7 @@ static vm_fault_t hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
 				make_huge_pte(vma, new_page, 1));
 		page_remove_rmap(old_page, true);
 		hugepage_add_new_anon_rmap(new_page, vma, haddr);
-		SetHPageMigratable(new_page);
+		SetHPageMigratableIfSupported(new_page);
 		/* Make the old page be freed below */
 		new_page = old_page;
 	}
@@ -4436,7 +4436,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
 	 * been isolated for migration.
 	 */
 	if (new_page)
-		SetHPageMigratable(page);
+		SetHPageMigratableIfSupported(page);
 
 	unlock_page(page);
 out:
@@ -4747,7 +4747,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 
 	spin_unlock(ptl);
-	SetHPageMigratable(page);
+	SetHPageMigratableIfSupported(page);
 	if (vm_shared)
 		unlock_page(page);
 	ret = 0;
@@ -5589,7 +5589,7 @@ void putback_active_hugepage(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 	spin_lock(&hugetlb_lock);
-	SetHPageMigratable(page);
+	SetHPageMigratableIfSupported(page);
 	list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
 	spin_unlock(&hugetlb_lock);
 	put_page(page);
diff --git a/mm/migrate.c b/mm/migrate.c
index a3e1acc72ad7..c8d19e83f372 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1275,13 +1275,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	struct address_space *mapping = NULL;
 
 	/*
-	 * Migratability of hugepages depends on architectures and their size.
-	 * This check is necessary because some callers of hugepage migration
-	 * like soft offline and memory hotremove don't walk through page
-	 * tables or check whether the hugepage is pmd-based or not before
-	 * kicking migration.
+	 * Support for migration should be checked at isolation time.
+	 * Therefore, we should never get here if migration is not supported
+	 * for the page.
 	 */
 	if (!hugepage_migration_supported(page_hstate(hpage))) {
+		VM_WARN_ON(1);
 		list_move_tail(&hpage->lru, ret);
 		return -ENOSYS;
 	}
-- 
2.29.2