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Date:   Wed, 11 Nov 2020 16:38:48 +0000
From:   Matthew Wilcox <willy@infradead.org>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Liang, Kan" <kan.liang@linux.intel.com>,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>, mingo@redhat.com,
        acme@kernel.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, eranian@google.com, ak@linux.intel.com,
        dave.hansen@intel.com, kirill.shutemov@linux.intel.com,
        benh@kernel.crashing.org, paulus@samba.org,
        David Miller <davem@davemloft.net>, vbabka@suse.cz
Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE
Message-ID: <20201111163848.GU17076@casper.infradead.org>
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On Wed, Nov 11, 2020 at 04:57:24PM +0100, Peter Zijlstra wrote:
> On Wed, Nov 11, 2020 at 03:30:22PM +0000, Matthew Wilcox wrote:
> > This confuses me.  Why only special-case hugetlbfs pages here?  Should
> > they really be treated differently from THP?  If you want to consider
> > that we might be mapping a page that's twice as big as a PUD entry and
> > this is only half of it, then the simple way is:
> > 
> > 	if (pud_leaf(pud)) {
> > #ifdef pud_page
> > 		page = compound_head(pud_page(*pud));
> > 		return page_size(page);
> 
> Also; this is 'wrong'. The purpose of this function is to return the
> hardware TLB size of a given address. The above will return the compound
> size, for any random compound page, which would be myrads of reasons.

Oh, then the whole thing is overly-complicated.  This should just be

	if (pud_leaf(pud))
		return PUD_SIZE;