From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 395772806E4 for ; Tue, 22 Aug 2017 11:02:03 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id k3so73325009pfc.0 for ; Tue, 22 Aug 2017 08:02:03 -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 j65si433146pgc.699.2017.08.22.08.02.00 for ; Tue, 22 Aug 2017 08:02:01 -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> From: Julien Thierry Message-ID: Date: Tue, 22 Aug 2017 16:01:56 +0100 MIME-Version: 1.0 In-Reply-To: <87wp5vmzpn.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 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. -- 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