Messages in this thread | | | Subject | Re: [PATCH V6 01/16] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE | From | Dave Hansen <> | Date | Mon, 10 Aug 2020 14:47:11 -0700 |
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On 8/10/20 2:24 PM, Kan Liang wrote: > +static u64 __perf_get_page_size(struct mm_struct *mm, unsigned long addr) > +{ > + struct page *page; > + pgd_t *pgd; > + p4d_t *p4d; > + pud_t *pud; > + pmd_t *pmd; > + pte_t *pte; > + > + pgd = pgd_offset(mm, addr); > + if (pgd_none(*pgd)) > + return 0; > + > + p4d = p4d_offset(pgd, addr); > + if (!p4d_present(*p4d)) > + return 0; > + > +#if (defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)) > + if (p4d_leaf(*p4d)) { > + page = p4d_page(*p4d); > + > + if (PageCompound(page)) > + return page_size(compound_head(page)); > + > + return P4D_SIZE; > + } > +#endif > + > + pud = pud_offset(p4d, addr); > + if (!pud_present(*pud)) > + return 0; > + > +#if (defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)) > + if (pud_leaf(*pud)) { > + page = pud_page(*pud); > + > + if (PageCompound(page)) > + return page_size(compound_head(page)); > + > + return PUD_SIZE; > + } > +#endif > + > + pmd = pmd_offset(pud, addr); > + if (!pmd_present(*pmd)) > + return 0; > + > +#if (defined(CONFIG_HUGETLB_PAGE) || defined(CONFIG_TRANSPARENT_HUGEPAGE)) > + if (pmd_leaf(*pmd)) { > + page = pmd_page(*pmd); > + > + if (PageCompound(page)) > + return page_size(compound_head(page)); > + > + return PMD_SIZE; > + } > +#endif > + > + pte = pte_offset_map(pmd, addr); > + if (!pte_present(*pte)) { > + pte_unmap(pte); > + return 0; > + } > + > + pte_unmap(pte); > + return PAGE_SIZE; > +}
It's probably best if we very carefully define up front what is getting reported here. For instance, I believe we already have some fun cases with huge tmpfs where a compound page is mapped with 4k PTEs. Kirill also found a few drivers doing this as well. I think there were also some weird cases for ARM hugetlbfs where there were multiple hardware page table entries mapping a single hugetlbfs page. These would be cases where compound_head() size would be greater than the size of the leaf paging structure entry.
This is also why we have KerelPageSize and MMUPageSize in /proc/$pid/smaps.
So, is this returning the kernel software page size or the MMU size?
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