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    SubjectRe: [PATCH V6 01/16] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE
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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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      Last update: 2020-08-10 23:47    [W:12.082 / U:0.020 seconds]
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