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

[Peter Zijlstra]

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;
> +}