On 13.01.21 06:22, Muchun Song wrote:
> All pages isolated for the migration have an elevated reference count
> and therefore seeing a reference count equal to 1 means that the last
> user of the page has dropped the reference and the page has became
> unused and there doesn't make much sense to migrate it anymore. This has
> been done for regular pages and this patch does the same for hugetlb
> pages. Although the likelyhood of the race is rather small for hugetlb
> pages it makes sense the two code paths in sync.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Acked-by: Yang Shi <shy828301@xxxxxxxxx>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> 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;
>
Happy to say that I now know understand what's going on here
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
--
Thanks,
David / dhildenb
