On Fri, Jan 22, 2021 at 11:52:29AM -0800, Mike Kravetz wrote:
> 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>
I wish there was a better way to do this like opencode it at fault path,
but as you mentioned that is troublesome.
I am not a big fan of the name either, too long for my taste but I cannot
come up with anything better so:
Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>
> ---
> 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
>
>
--
Oscar Salvador
SUSE L3
