On Fri, Aug 14, 2020 at 10:37:29AM +0800, Ming Mao wrote:
> +static long hugetlb_page_vaddr_get_pfn(unsigned long vaddr, long npage,
> + unsigned long pfn)
> +{
> + long hugetlb_residual_npage;
> + long contiguous_npage;
> + struct page *head = compound_head(pfn_to_page(pfn));
> +
> + /*
> + * If pfn is valid,
> + * hugetlb_residual_npage is greater than or equal to 1.
> + */
> + hugetlb_residual_npage = hugetlb_get_residual_pages(vaddr,
> + compound_order(head));
> + if (hugetlb_residual_npage < 0)
> + return -1;
> +
> + /* The page of vaddr has been gotten by vaddr_get_pfn */
> + contiguous_npage = min_t(long, (hugetlb_residual_npage - 1), npage);
> + if (!contiguous_npage)
> + return 0;
> + /*
> + * Unlike THP, the splitting should not happen for hugetlb pages.
> + * Since PG_reserved is not relevant for compound pages, and the pfn of
> + * PAGE_SIZE page which in hugetlb pages is valid,
> + * it is not necessary to check rsvd for hugetlb pages.
> + * We do not need to alloc pages because of vaddr and we can finish all
> + * work by a single operation to the head page.
> + */
> + atomic_add(contiguous_npage, compound_pincount_ptr(head));
> + page_ref_add(head, contiguous_npage);
> + mod_node_page_state(page_pgdat(head), NR_FOLL_PIN_ACQUIRED, contiguous_npage);
I think I asked this question in v1, but I didn't get any answer... So I'm
trying again...
Could I ask why manual referencing of pages is done here rather than using
pin_user_pages_remote() just like what we've done with vaddr_get_pfn(), and let
try_grab_page() to do the page reference and accountings?
I feel like this at least is against the FOLL_PIN workflow of gup, because
those FOLL_PIN paths were bypassed, afaict.
> +
> + return contiguous_npage;
> +}
--
Peter Xu
