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SubjectRe: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one
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On 10.01.21 13:40, 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.
>
> This optimization is consistent with the regular pages, just like
> unmap_and_move() does.
>
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> Acked-by: Yang Shi <shy828301@gmail.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;
>

Question: What if called via alloc_contig_range() where we even want to
"migrate" free pages, meaning, relocate it?

--
Thanks,

David / dhildenb

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