On 8/10/2020 5:47 PM, Dave Hansen wrote:
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?
This tries to return the kernel software page size. I will add a commit to the function. For the above cases, I think they can be detected by PageCompound(page). The current code should already cover them. Is my understanding correct?
Thanks, Kan
