On Mon, Oct 26, 2020 at 10:51:00PM +0800, Muchun Song wrote:
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#define VMEMMAP_HPAGE_SHIFT PMD_SHIFT
> +#define arch_vmemmap_support_huge_mapping() boot_cpu_has(X86_FEATURE_PSE)
I do not think you need this.
We already have hugepages_supported().
> +#ifdef CONFIG_HUGETLB_PAGE_FREE_VMEMMAP
> +#ifndef arch_vmemmap_support_huge_mapping
> +static inline bool arch_vmemmap_support_huge_mapping(void)
> +{
> + return false;
> +}
Same as above
> static inline unsigned int nr_free_vmemmap(struct hstate *h)
> {
> return h->nr_free_vmemmap_pages;
> }
>
> +static inline unsigned int nr_vmemmap(struct hstate *h)
> +{
> + return nr_free_vmemmap(h) + RESERVE_VMEMMAP_NR;
> +}
> +
> +static inline unsigned long nr_vmemmap_size(struct hstate *h)
> +{
> + return (unsigned long)nr_vmemmap(h) << PAGE_SHIFT;
> +}
> +
> +static inline unsigned int nr_pgtable(struct hstate *h)
> +{
> + unsigned long vmemmap_size = nr_vmemmap_size(h);
> +
> + if (!arch_vmemmap_support_huge_mapping())
> + return 0;
> +
> + /*
> + * No need pre-allocate page tabels when there is no vmemmap pages
> + * to free.
> + */
> + if (!nr_free_vmemmap(h))
> + return 0;
> +
> + return ALIGN(vmemmap_size, VMEMMAP_HPAGE_SIZE) >> VMEMMAP_HPAGE_SHIFT;
> +}
IMHO, Mike's naming suggestion fit much better.
> +static void vmemmap_pgtable_deposit(struct page *page, pte_t *pte_p)
> +{
> + pgtable_t pgtable = virt_to_page(pte_p);
> +
> + /* FIFO */
> + if (!page_huge_pte(page))
> + INIT_LIST_HEAD(&pgtable->lru);
> + else
> + list_add(&pgtable->lru, &page_huge_pte(page)->lru);
> + page_huge_pte(page) = pgtable;
> +}
I think it would make more sense if this took a pgtable argument
instead of a pte_t *.
> +static pte_t *vmemmap_pgtable_withdraw(struct page *page)
> +{
> + pgtable_t pgtable;
> +
> + /* FIFO */
> + pgtable = page_huge_pte(page);
> + if (unlikely(!pgtable))
> + return NULL;
AFAICS, above check only needs to be run once.
It think we can move it to vmemmap_pgtable_free, can't we?
> + page_huge_pte(page) = list_first_entry_or_null(&pgtable->lru,
> + struct page, lru);
> + if (page_huge_pte(page))
> + list_del(&pgtable->lru);
> + return page_to_virt(pgtable);
> +}
At the risk of adding more code, I think it would be nice to return a
pagetable_t?
So it is more coherent with the name of the function and with what
we are doing.
It is a pitty we cannot converge these and pgtable_trans_huge_*.
They share some code but it is different enough.
> +static int vmemmap_pgtable_prealloc(struct hstate *h, struct page *page)
> +{
> + int i;
> + pte_t *pte_p;
> + unsigned int nr = nr_pgtable(h);
> +
> + if (!nr)
> + return 0;
> +
> + vmemmap_pgtable_init(page);
Maybe just open code this one?
> +static inline void vmemmap_pgtable_free(struct hstate *h, struct page *page)
> +{
> + pte_t *pte_p;
> +
> + if (!nr_pgtable(h))
> + return;
> +
> + while ((pte_p = vmemmap_pgtable_withdraw(page)))
> + pte_free_kernel(&init_mm, pte_p);
As mentioned above, move the pgtable_t check from vmemmap_pgtable_withdraw
in here.
> static void prep_new_huge_page(struct hstate *h, struct page *page, int nid)
> {
> + /* Must be called before the initialization of @page->lru */
> + vmemmap_pgtable_free(h, page);
> +
> INIT_LIST_HEAD(&page->lru);
> set_compound_page_dtor(page, HUGETLB_PAGE_DTOR);
> set_hugetlb_cgroup(page, NULL);
> @@ -1783,6 +1892,14 @@ static struct page *alloc_fresh_huge_page(struct hstate *h,
> if (!page)
> return NULL;
>
> + if (vmemmap_pgtable_prealloc(h, page)) {
> + if (hstate_is_gigantic(h))
> + free_gigantic_page(page, huge_page_order(h));
> + else
> + put_page(page);
> + return NULL;
> + }
> +
I must confess I am bit puzzled.
IIUC, in this patch we are just adding the helpers to create/tear the page
tables.
I do not think we actually need to call vmemmap_pgtable_prealloc/vmemmap_pgtable_free, do we?
In the end, we are just allocating pages for pagetables and then free them shortly.
I think it would make more sense to add the calls when they need to be?
--
Oscar Salvador
SUSE L3
