On Fri 22-01-21 11:52:29, 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>
> ---
> 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)
This is really mouthful...
> +{
> + if (hugepage_migration_supported(page_hstate(page)))
> + SetHPageMigratable(page);
and it is really a trivial wrapper. I do understand why you want to
prevent from the code duplication and potentially a missing check but
this all is just an internal hugetlb code. Even if the flag is set on
non-migrateable hugetlb page then this will not be fatal. The migration
can fail even on those pages for which migration is supported right?
So I am not really sure this is an improvement in the end. But up to you
I do not really have a strong opinion here.
--
Michal Hocko
SUSE Labs
