[PATCH v2 3/5] hugetlb: only set HPageMigratable for migratable hstates

Mike Kravetz
2021-01-20T02:05:58Z

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@oracle.com>
---
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 ec9f03aa2738..8b8acdafd0be 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 ce3d03da0133..1e17529c8b81 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -744,6 +744,15 @@ 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 c24da40626d3..6e32751489e8 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4196,7 +4196,7 @@ 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;
}
@@ -4438,7 +4438,7 @@ 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:
@@ -4749,7 +4749,7 @@ 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;
@@ -5584,7 +5584,7 @@ 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 0339f3874d7c..943391cd1a7c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1273,13 +1273,12 @@ 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