From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id C95762806E4 for ; Tue, 22 Aug 2017 12:18:10 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id r133so324983625pgr.6 for ; Tue, 22 Aug 2017 09:18:10 -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 o33si9879311plb.1041.2017.08.22.09.18.08 for ; Tue, 22 Aug 2017 09:18:09 -0700 (PDT) From: Punit Agrawal 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> Date: Tue, 22 Aug 2017 17:18:04 +0100 In-Reply-To: (Julien Thierry's message of "Tue, 22 Aug 2017 16:01:56 +0100") Message-ID: <87inhfmv9f.fsf@e105922-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: Julien Thierry 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 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. Thanks, Punit -- 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