Re: [PATCH v2 4/4] hugetlb: add hugetlb demote page support

[David Hildenbrand]

On 23.09.21 19:53, Mike Kravetz wrote:
> Demote page functionality will split a huge page into a number of huge
> pages of a smaller size.  For example, on x86 a 1GB huge page can be
> demoted into 512 2M huge pages.  Demotion is done 'in place' by simply
> splitting the huge page.
>
> Added '*_for_demote' wrappers for remove_hugetlb_page,
> destroy_compound_gigantic_page and prep_compound_gigantic_page for use
> by demote code.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> ---
>   mm/hugetlb.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++---
>   1 file changed, 75 insertions(+), 4 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 2317d411243d..ab7bd0434057 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1260,7 +1260,7 @@ static int hstate_next_node_to_free(struct hstate *h, nodemask_t *nodes_allowed)
>   		((node = hstate_next_node_to_free(hs, mask)) || 1);	\
>   		nr_nodes--)
>   
> -#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
> +/* used to demote non-gigantic_huge pages as well */
>   static void __destroy_compound_gigantic_page(struct page *page,
>   					unsigned int order, bool demote)
>   {
> @@ -1283,6 +1283,13 @@ static void __destroy_compound_gigantic_page(struct page *page,
>   	__ClearPageHead(page);
>   }
>   
> +static void destroy_compound_gigantic_page_for_demote(struct page *page,
> +					unsigned int order)
> +{
> +	__destroy_compound_gigantic_page(page, order, true);
> +}
> +
> +#ifdef CONFIG_ARCH_HAS_GIGANTIC_PAGE
>   static void destroy_compound_gigantic_page(struct page *page,
>   					unsigned int order)
>   {
> @@ -1428,6 +1435,12 @@ static void remove_hugetlb_page(struct hstate *h, struct page *page,
>   	__remove_hugetlb_page(h, page, adjust_surplus, false);
>   }
>   
> +static void remove_hugetlb_page_for_demote(struct hstate *h, struct page *page,
> +							bool adjust_surplus)
> +{
> +	__remove_hugetlb_page(h, page, adjust_surplus, true);
> +}
> +
>   static void add_hugetlb_page(struct hstate *h, struct page *page,
>   			     bool adjust_surplus)
>   {
> @@ -1777,6 +1790,12 @@ static bool prep_compound_gigantic_page(struct page *page, unsigned int order)
>   	return __prep_compound_gigantic_page(page, order, false);
>   }
>   
> +static bool prep_compound_gigantic_page_for_demote(struct page *page,
> +							unsigned int order)
> +{
> +	return __prep_compound_gigantic_page(page, order, true);
> +}
> +
>   /*
>    * PageHuge() only returns true for hugetlbfs pages, but not for normal or
>    * transparent huge pages.  See the PageTransHuge() documentation for more
> @@ -3298,9 +3317,55 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
>   	return 0;
>   }
>   
> +static int demote_free_huge_page(struct hstate *h, struct page *page)
> +{
> +	int i, nid = page_to_nid(page);
> +	struct hstate *target_hstate;
> +	bool cma_page = HPageCma(page);
> +
> +	target_hstate = size_to_hstate(PAGE_SIZE << h->demote_order);
> +
> +	remove_hugetlb_page_for_demote(h, page, false);
> +	spin_unlock_irq(&hugetlb_lock);
> +
> +	if (alloc_huge_page_vmemmap(h, page)) {
> +		/* Allocation of vmemmmap failed, we can not demote page */
> +		spin_lock_irq(&hugetlb_lock);
> +		set_page_refcounted(page);
> +		add_hugetlb_page(h, page, false);

I dislike using 0/1 as return values as it will just hide the actual issue.

This here would be -ENOMEM, right?



--
Thanks,

David / dhildenb