-----邮件原件----- 发件人: Peter Xu [mailto:peterx@xxxxxxxxxx] 发送时间: 2020年8月26日 4:59 收件人: Maoming (maoming, Cloud Infrastructure Service Product Dept.) <maoming.maoming@xxxxxxxxxx> 抄送: linux-kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; alex.williamson@xxxxxxxxxx; cohuck@xxxxxxxxxx; Zhoujian (jay) <jianjay.zhou@xxxxxxxxxx>; Huangweidong (C) <weidong.huang@xxxxxxxxxx>; aarcange@xxxxxxxxxx 主题: Re: [PATCH V2] vfio dma_map/unmap: optimized for hugetlbfs pages 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. Hi, My apologies for not answering your question. As I understand, pin_user_pages_remote() might spend much time. Because all PAGE_SIZE-pages in a hugetlb page are pinned one by one in pin_user_pages_remote() and try_grab_page(). So I think maybe we can use these simple code to do all work. Am I wrong? And is there something else we can use? For example :pin_user_pages_fast() > + > + return contiguous_npage; > +} -- Peter Xu
