Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page to workaround the nasty free_huge_page

Baoquan He
2020-08-10T02:17:52Z

On 08/07/20 at 05:12pm, Wei Yang wrote:
> Let's always increase surplus_huge_pages and so that free_huge_page
> could decrease it at free time.
>
> Signed-off-by: Wei Yang <richard.weiyang@linux.alibaba.com>
> ---
> mm/hugetlb.c | 14 ++++++--------
> 1 file changed, 6 insertions(+), 8 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1f2010c9dd8d..a0eb81e0e4c5 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1913,21 +1913,19 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
> return NULL;
>
> spin_lock(&hugetlb_lock);
> +
> + h->surplus_huge_pages++;
> + h->surplus_huge_pages_node[page_to_nid(page)]++;
> +
> /*
> * We could have raced with the pool size change.
> * Double check that and simply deallocate the new page
> - * if we would end up overcommiting the surpluses. Abuse
> - * temporary page to workaround the nasty free_huge_page
> - * codeflow
> + * if we would end up overcommiting the surpluses.
> */
> - if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
> - SetPageHugeTemporary(page);

Hmm, the temporary page way is taken intentionally in
commit 9980d744a0428 ("mm, hugetlb: get rid of surplus page accounting tricks").
From code, this is done inside hugetlb_lock holding, and the code flow
is straightforward, should be safe. Adding Michal to CC.

> + if (h->surplus_huge_pages > h->nr_overcommit_huge_pages) {
> spin_unlock(&hugetlb_lock);
> put_page(page);
> return NULL;
> - } else {
> - h->surplus_huge_pages++;
> - h->surplus_huge_pages_node[page_to_nid(page)]++;
> }
>
> out_unlock:
> --
> 2.20.1 (Apple Git-117)
>
>