linux-kernel - Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Date:   Fri, 9 Oct 2020 08:29:25 -0400
From:   "Liang, Kan" <kan.liang@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, eranian@...gle.com, ak@...ux.intel.com,
        dave.hansen@...el.com, kirill.shutemov@...ux.intel.com,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        Will Deacon <will@...nel.org>,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE



On 10/9/2020 5:09 AM, Peter Zijlstra wrote:
> (we might not need the #ifdef gunk, but I've not yet dug out my cross
>   compilers this morning)
> 
> ---
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7009,6 +7009,7 @@ static u64 perf_virt_to_phys(u64 virt)
>    */
>   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;
> @@ -7030,15 +7031,27 @@ static u64 __perf_get_page_size(struct m
>   	if (!pud_present(*pud))
>   		return 0;
>   
> -	if (pud_leaf(*pud))
> +	if (pud_leaf(*pud)) {
> +#ifdef pud_page
> +		page = pud_page(*pud);
> +		if (PageHuge(page))
> +			return page_size(compound_head(page));

I think the page_size() returns the Kernel Page Size of a compound page.
What we want is the MMU page size.

If it's for the generic code, I think it should be a problem for X86.

Thanks,
Kan

> +#endif
>   		return 1ULL << PUD_SHIFT;
> +	}
>   
>   	pmd = pmd_offset(pud, addr);
>   	if (!pmd_present(*pmd))
>   		return 0;
>   
> -	if (pmd_leaf(*pmd))
> +	if (pmd_leaf(*pmd)) {
> +#ifdef pmd_page
> +		page = pmd_page(*pmd);
> +		if (PageHuge(page))
> +			return page_size(compound_head(page));
> +#endif
>   		return 1ULL << PMD_SHIFT;
> +	}
>   
>   	pte = pte_offset_map(pmd, addr);
>   	if (!pte_present(*pte)) {
> @@ -7046,6 +7059,10 @@ static u64 __perf_get_page_size(struct m
>   		return 0;
>   	}
>   
> +	page = pte_page(*pte);
> +	if (PageHuge(page))
> +		return page_size(compound_head(page));
> +
>   	pte_unmap(pte);
>   	return PAGE_SIZE;
>   }