Re: [PATCH 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one

Michal Hocko
2021-01-06T16:11:43Z

On Mon 04-01-21 14:58:38, Muchun Song wrote:
> If the refcount is one when it is migrated, it means that the page
> was freed from under us. So we are done and do not need to migrate.

Is this common enough that it would warrant the explicit check for each
migration?

> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
> mm/migrate.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index 4385f2fb5d18..a6631c4eb6a6 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
> return -ENOSYS;
> }
>
> + if (page_count(hpage) == 1) {
> + /* page was freed from under us. So we are done. */
> + putback_active_hugepage(hpage);
> + return MIGRATEPAGE_SUCCESS;
> + }
> +
> new_hpage = get_new_page(hpage, private);
> if (!new_hpage)
> return -ENOMEM;
> --
> 2.11.0

--
Michal Hocko
SUSE Labs