[PATCH 3/5] hugetlb: only set HP_Migratable 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.  The check
in unmap_and_move_huge_page for migration support can be removed as it
is no longer necessary.  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.

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            | 12 ------------
 4 files changed, 14 insertions(+), 17 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 89bc9062b4f6..14d77d01e38d 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]);
 
-		hugetlb_set_page_flag(page, HP_Migratable);
+		hugetlb_set_HP_Migratable(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 353d81913cc7..e7157cf9967f 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -716,6 +716,15 @@ static inline bool hugepage_migration_supported(struct hstate *h)
 	return arch_hugetlb_migration_supported(h);
 }
 
+/*
+ * Only set flag if hstate supports migration
+ */
+static inline void hugetlb_set_HP_Migratable(struct page *page)
+{
+	if (hugepage_migration_supported(page_hstate(page)))
+		hugetlb_set_page_flag(page, HP_Migratable);
+}
+
 /*
  * 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 c43cebf2f278..31e896c70ba0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4197,7 +4197,7 @@ 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);
-		hugetlb_set_page_flag(new_page, HP_Migratable);
+		hugetlb_set_HP_Migratable(new_page);
 		/* Make the old page be freed below */
 		new_page = old_page;
 	}
@@ -4439,7 +4439,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
 	 * been isolated for migration.
 	 */
 	if (new_page)
-		hugetlb_set_page_flag(page, HP_Migratable);
+		hugetlb_set_HP_Migratable(page);
 
 	unlock_page(page);
 out:
@@ -4750,7 +4750,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 	update_mmu_cache(dst_vma, dst_addr, dst_pte);
 
 	spin_unlock(ptl);
-	hugetlb_set_page_flag(page, HP_Migratable);
+	hugetlb_set_HP_Migratable(page);
 	if (vm_shared)
 		unlock_page(page);
 	ret = 0;
@@ -5585,7 +5585,7 @@ void putback_active_hugepage(struct page *page)
 {
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 	spin_lock(&hugetlb_lock);
-	hugetlb_set_page_flag(page, HP_Migratable);
+	hugetlb_set_HP_Migratable(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 0339f3874d7c..296d61613abc 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1272,18 +1272,6 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	struct anon_vma *anon_vma = NULL;
 	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.
-	 */
-	if (!hugepage_migration_supported(page_hstate(hpage))) {
-		list_move_tail(&hpage->lru, ret);
-		return -ENOSYS;
-	}
-
 	if (page_count(hpage) == 1) {
 		/* page was freed from under us. So we are done. */
 		putback_active_hugepage(hpage);
-- 
2.29.2