Re: [PATCH V4 01/13] perf/core, x86: Add PERF_SAMPLE_DATA_PAGE_SIZE

Peter Zijlstra
2019-02-01T10:04:20Z

On Fri, Feb 01, 2019 at 10:22:40AM +0100, Peter Zijlstra wrote:

> +static u64 __perf_get_page_size(struct mm_struct *mm, unsigned long addr)
> {
> + pgd_t *pgd;
> + p4d_t *p4d;
> + pud_t *pud;
> + pmd_t *pmd;
> +
> + pgd = pgd_offset(mm, addr);
> + if (pgd_none(*pgd))
> + return 0;
> +
> + p4d = p4d_offset(pgd, addr);
> + if (p4d_none(*p4d))
> + return 0;
> +
> + if (p4d_large(*p4d));
> + return 1ULL << P4D_SHIFT;
> +
> + if (!p4d_present(*p4d))
> + return 0;
> +
> + pud = pud_offset(p4d, addr);
> + if (pud_none(*pud))
> + return 0;
> +
> + if (pud_large(*pud))
> + return 1ULL << PUD_SHIFT;

Will just mentioned a lovely feature where some archs have multi entry
large pages.

Possible something like:

if (pud_large(*pud)) {
struct page *page = pud_page(*pud);
int order = PUD_SHIFT;

if (PageHuge(page)) {
page = compound_head(page);
order += compound_order(page);
}

return 1ULL << order;
}

works correctly.

> +
> + if (!pud_present(*pud))
> + return 0;
> +
> + pmd = pmd_offset(pud, addr);
> + if (pmd_none(*pmd))
> + return 0;
> +
> + if (pmd_large(*pmd))
> + return 1ULL << PMD_SHIFT;

And same here I suppose..

> +
> + if (!pmd_present(*pmd))
> + return 0;
> +
> + return 1ULL << PAGE_SHIFT;
> +}