From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 612B02806E4 for ; Tue, 22 Aug 2017 12:21:08 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id 83so326283572pgb.14 for ; Tue, 22 Aug 2017 09:21:08 -0700 (PDT) Received: from foss.arm.com (usa-sjc-mx-foss1.foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id e3si9083424pga.511.2017.08.22.09.21.06 for ; Tue, 22 Aug 2017 09:21:07 -0700 (PDT) Subject: Re: [PATCH v7 5/9] arm64: hugetlb: Handle swap entries in huge_pte_offset() for contiguous hugepages References: <20170822104249.2189-1-punit.agrawal@arm.com> <20170822104249.2189-6-punit.agrawal@arm.com> <87wp5vmzpn.fsf@e105922-lin.cambridge.arm.com> <87inhfmv9f.fsf@e105922-lin.cambridge.arm.com> From: Julien Thierry Message-ID: <010915f9-2322-1add-bf9a-dc0e830d6548@arm.com> Date: Tue, 22 Aug 2017 17:21:02 +0100 MIME-Version: 1.0 In-Reply-To: <87inhfmv9f.fsf@e105922-lin.cambridge.arm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Punit Agrawal Cc: will.deacon@arm.com, catalin.marinas@arm.com, mark.rutland@arm.com, David Woods , steve.capper@arm.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org On 22/08/17 17:18, Punit Agrawal wrote: > Julien Thierry writes: > >> On 22/08/17 15:41, Punit Agrawal wrote: >>> Julien Thierry writes: >>> >>>> Hi Punit, >>>> >>>> On 22/08/17 11:42, Punit Agrawal wrote: >>>>> huge_pte_offset() was updated to correctly handle swap entries for >>>>> hugepages. With the addition of the size parameter, it is now possible >>>>> to disambiguate whether the request is for a regular hugepage or a >>>>> contiguous hugepage. >>>>> >>>>> Fix huge_pte_offset() for contiguous hugepages by using the size to find >>>>> the correct page table entry. >>>>> >>>>> Signed-off-by: Punit Agrawal >>>>> Cc: David Woods >>>>> --- >>>>> arch/arm64/mm/hugetlbpage.c | 21 ++++++++++++++++----- >>>>> 1 file changed, 16 insertions(+), 5 deletions(-) >>>>> >>>>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c >>>>> index 594232598cac..b95e24dc3477 100644 >>>>> --- a/arch/arm64/mm/hugetlbpage.c >>>>> +++ b/arch/arm64/mm/hugetlbpage.c >>>>> @@ -214,6 +214,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, >>>>> pgd_t *pgd; >>>>> pud_t *pud; >>>>> pmd_t *pmd; >>>>> + pte_t *pte; >>>>> pgd = pgd_offset(mm, addr); >>>>> pr_debug("%s: addr:0x%lx pgd:%p\n", __func__, addr, pgd); >>>>> @@ -221,19 +222,29 @@ pte_t *huge_pte_offset(struct mm_struct *mm, >>>>> return NULL; >>>>> pud = pud_offset(pgd, addr); >>>>> - if (pud_none(*pud)) >>>>> + if (sz != PUD_SIZE && pud_none(*pud)) >>>>> return NULL; >>>>> - /* swap or huge page */ >>>>> - if (!pud_present(*pud) || pud_huge(*pud)) >>>>> + /* hugepage or swap? */ >>>>> + if (pud_huge(*pud) || !pud_present(*pud)) >>>>> return (pte_t *)pud; >>>>> /* table; check the next level */ >>>>> + if (sz == CONT_PMD_SIZE) >>>>> + addr &= CONT_PMD_MASK; >>>>> + >>>>> pmd = pmd_offset(pud, addr); >>>>> - if (pmd_none(*pmd)) >>>>> + if (!(sz == PMD_SIZE || sz == CONT_PMD_SIZE) && >>>>> + pmd_none(*pmd)) >>>>> return NULL; >>>>> - if (!pmd_present(*pmd) || pmd_huge(*pmd)) >>>>> + if (pmd_huge(*pmd) || !pmd_present(*pmd)) >>>>> return (pte_t *)pmd; >>>>> + if (sz == CONT_PTE_SIZE) { >>>>> + pte = pte_offset_kernel( >>>>> + pmd, (addr & CONT_PTE_MASK)); >>>>> + return pte; >>>> >>>> Nit: Looks like this is the only place the new variable pte is >>>> used. Since we don't need to test its value, why not just write: >>>> return pte_offset_kernel(pmd, (addr & CONT_PTE_MASK)); >>>> >>>> and get rid of the pte variable? >>> >>> There is no benefit to getting rid of "pte" other than conciseness of >>> the patch. Having an explicit identifier helps highlight the level of >>> the page tables we are accessing. >>> >>> And we always want to prioritise readability vs conciseness of the >>> patch, no? >>> >> >> I agree, but I feel here it is more redundancy than increase of >> readability, because we know pte_offset_kernel returns the address of >> a pte, no? (otherwise I feel a comment would fit better than a >> variable). >> >> Also, we end up with a variable declared in one scope where it is not >> used, and it is referenced in a single inner scope, which seems a bit >> odd to me. Might make the reader pointlessly wonder where else it is >> used. > > I would've thought looking at the function makes the variable usage > quite clear. But I think at this stage we are disagreeing over personal > preferences rather than any real issues (imho) with the code. > > If you feel strongly about this, I can update the code if there is a > need for another version. But I am reluctant to send a new version just > for this change. > Fair enough, it was just nitpicking. Rest of the patchset looks good from my understanding. Cheers, -- Julien Thierry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org