On Fri, Jun 11, 2021 at 09:31:16PM -0700, Hugh Dickins wrote:
> +++ linux/include/linux/pagemap.h 2021-06-11 17:30:28.726720252 -0700
> @@ -516,8 +516,7 @@ static inline struct page *read_mapping_
> }
>
> /*
> - * Get index of the page with in radix-tree
> - * (TODO: remove once hugetlb pages will have ->index in PAGE_SIZE)
> + * Get index of the page within radix-tree (but not for hugetlb pages).
> */
I think the TODO should be retained. It's still something that I
intend to do.
> static inline pgoff_t page_to_pgoff(struct page *page)
> {
> - if (unlikely(PageHeadHuge(page)))
> - return page->index << compound_order(page);
> -
> + if (unlikely(PageHuge(page))) {
> + extern pgoff_t hugetlb_basepage_index(struct page *page);
> + return hugetlb_basepage_index(page);
> + }
> return page_to_index(page);
> }
Yes, this change absolutely makes sense. It's just a landmine if it
returns the right answer for some tail pages but garbage for other
kinds of tail pages.
> --- 5.13-rc5/mm/hugetlb.c 2021-06-06 16:57:26.263006733 -0700
> +++ linux/mm/hugetlb.c 2021-06-11 17:30:28.730720276 -0700
> @@ -1588,15 +1588,12 @@ struct address_space *hugetlb_page_mappi
> return NULL;
> }
>
> -pgoff_t __basepage_index(struct page *page)
> +pgoff_t hugetlb_basepage_index(struct page *page)
> {
> struct page *page_head = compound_head(page);
> pgoff_t index = page_index(page_head);
> unsigned long compound_idx;
>
> - if (!PageHuge(page_head))
> - return page_index(page);
> -
> if (compound_order(page_head) >= MAX_ORDER)
> compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
> else
>
urgh. this trailing bit should be:
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
compound_idx = page_to_pfn(page) - page_to_pfn(page_head);
#else
compound_idx = page - page_head;
#endif
