From: Anshuman Khandual <anshuman.khandual@arm.com> To: Yu Zhao <yuzhao@google.com> Cc: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>, Andrew Morton <akpm@linux-foundation.org>, Nick Piggin <npiggin@gmail.com>, Peter Zijlstra <peterz@infradead.org>, Joel Fernandes <joel@joelfernandes.org>, "Kirill A . Shutemov" <kirill@shutemov.name>, Mark Rutland <mark.rutland@arm.com>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Chintan Pandya <cpandya@codeaurora.org>, Jun Yao <yaojun8558363@gmail.com>, Laura Abbott <labbott@redhat.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Matthew Wilcox <willy@infradead.org> Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Date: Tue, 19 Feb 2019 11:47:12 +0530 [thread overview] Message-ID: <8f9b0bfb-b787-fa3e-7322-73a56a618aa8@arm.com> (raw) In-Reply-To: <20190219053205.GA124985@google.com> + Matthew Wilcox On 02/19/2019 11:02 AM, Yu Zhao wrote: > On Tue, Feb 19, 2019 at 09:51:01AM +0530, Anshuman Khandual wrote: >> >> >> On 02/19/2019 04:43 AM, Yu Zhao wrote: >>> For pte page, use pgtable_page_ctor(); for pmd page, use >>> pgtable_pmd_page_ctor() if not folded; and for the rest (pud, >>> p4d and pgd), don't use any. >> pgtable_page_ctor()/dtor() is not optional for any level page table page >> as it determines the struct page state and zone statistics. > > This is not true. pgtable_page_ctor() is only meant for user pte > page. The name isn't perfect (we named it this way before we had > split pmd page table lock, and never bothered to change it). > > The commit cccd843f54be ("mm: mark pages in use for page tables") > clearly states so: > Note that only pages currently accounted as NR_PAGETABLES are > tracked as PageTable; this does not include pgd/p4d/pud/pmd pages. I think the commit is the following one and it does say so. But what is the rationale of tagging only PTE page as PageTable and updating the zone stat but not doing so for higher level page table pages ? Are not they used as page table pages ? Should not they count towards NR_PAGETABLE ? 1d40a5ea01d53251c ("mm: mark pages in use for page tables") > > I'm sure if we go back further, we can find similar stories: we > don't set PageTable on page tables other than pte; and we don't > account page tables other than pte. I don't have any objection if > you want change these two. But please make sure they are consistent > across all archs. pgtable_page_ctor/dtor() use across arch is not consistent and there is a need for generalization which has been already acknowledged earlier. But for now we can atleast fix this on arm64. https://lore.kernel.org/lkml/1547619692-7946-1-git-send-email-anshuman.khandual@arm.com/ > >> We should not skip it for any page table page. > > In fact, calling it on pmd/pud/p4d is peculiar, and may even be > considered wrong. AFAIK, no other arch does so. Why would it be considered wrong ? IIUC archs have their own understanding of this and there are different implementations. But doing something for PTE page and skipping for others is plain inconsistent. > >> As stated before pgtable_pmd_page_ctor() is not a replacement for >> pgtable_page_ctor(). > > pgtable_pmd_page_ctor() must be used on user pmd. For kernel pmd, > it's okay to use pgtable_page_ctor() instead only because kernel > doesn't have thp. The only extra thing to be done for THP is initializing page->pmd_huge_pte apart from calling pgtable_page_ctor(). Right not it just works on arm64 may be because page->pmd_huge_pte never gets accessed before it's init and no path checks for it when not THP. Its better to init/reset pmd_huge_pte.
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From: Anshuman Khandual <anshuman.khandual@arm.com> To: Yu Zhao <yuzhao@google.com> Cc: Mark Rutland <mark.rutland@arm.com>, linux-arch@vger.kernel.org, Matthew Wilcox <willy@infradead.org>, Ard Biesheuvel <ard.biesheuvel@linaro.org>, Peter Zijlstra <peterz@infradead.org>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org, Nick Piggin <npiggin@gmail.com>, Jun Yao <yaojun8558363@gmail.com>, linux-mm@kvack.org, "Aneesh Kumar K . V" <aneesh.kumar@linux.vnet.ibm.com>, Chintan Pandya <cpandya@codeaurora.org>, Joel Fernandes <joel@joelfernandes.org>, "Kirill A . Shutemov" <kirill@shutemov.name>, Andrew Morton <akpm@linux-foundation.org>, Laura Abbott <labbott@redhat.com>, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Date: Tue, 19 Feb 2019 11:47:12 +0530 [thread overview] Message-ID: <8f9b0bfb-b787-fa3e-7322-73a56a618aa8@arm.com> (raw) In-Reply-To: <20190219053205.GA124985@google.com> + Matthew Wilcox On 02/19/2019 11:02 AM, Yu Zhao wrote: > On Tue, Feb 19, 2019 at 09:51:01AM +0530, Anshuman Khandual wrote: >> >> >> On 02/19/2019 04:43 AM, Yu Zhao wrote: >>> For pte page, use pgtable_page_ctor(); for pmd page, use >>> pgtable_pmd_page_ctor() if not folded; and for the rest (pud, >>> p4d and pgd), don't use any. >> pgtable_page_ctor()/dtor() is not optional for any level page table page >> as it determines the struct page state and zone statistics. > > This is not true. pgtable_page_ctor() is only meant for user pte > page. The name isn't perfect (we named it this way before we had > split pmd page table lock, and never bothered to change it). > > The commit cccd843f54be ("mm: mark pages in use for page tables") > clearly states so: > Note that only pages currently accounted as NR_PAGETABLES are > tracked as PageTable; this does not include pgd/p4d/pud/pmd pages. I think the commit is the following one and it does say so. But what is the rationale of tagging only PTE page as PageTable and updating the zone stat but not doing so for higher level page table pages ? Are not they used as page table pages ? Should not they count towards NR_PAGETABLE ? 1d40a5ea01d53251c ("mm: mark pages in use for page tables") > > I'm sure if we go back further, we can find similar stories: we > don't set PageTable on page tables other than pte; and we don't > account page tables other than pte. I don't have any objection if > you want change these two. But please make sure they are consistent > across all archs. pgtable_page_ctor/dtor() use across arch is not consistent and there is a need for generalization which has been already acknowledged earlier. But for now we can atleast fix this on arm64. https://lore.kernel.org/lkml/1547619692-7946-1-git-send-email-anshuman.khandual@arm.com/ > >> We should not skip it for any page table page. > > In fact, calling it on pmd/pud/p4d is peculiar, and may even be > considered wrong. AFAIK, no other arch does so. Why would it be considered wrong ? IIUC archs have their own understanding of this and there are different implementations. But doing something for PTE page and skipping for others is plain inconsistent. > >> As stated before pgtable_pmd_page_ctor() is not a replacement for >> pgtable_page_ctor(). > > pgtable_pmd_page_ctor() must be used on user pmd. For kernel pmd, > it's okay to use pgtable_page_ctor() instead only because kernel > doesn't have thp. The only extra thing to be done for THP is initializing page->pmd_huge_pte apart from calling pgtable_page_ctor(). Right not it just works on arm64 may be because page->pmd_huge_pte never gets accessed before it's init and no path checks for it when not THP. Its better to init/reset pmd_huge_pte. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-02-19 6:17 UTC|newest] Thread overview: 120+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-02-14 21:16 [PATCH] arm64: mm: enable per pmd page table lock Yu Zhao 2019-02-14 21:16 ` Yu Zhao 2019-02-18 15:12 ` Will Deacon 2019-02-18 15:12 ` Will Deacon 2019-02-18 19:49 ` Yu Zhao 2019-02-18 19:49 ` Yu Zhao 2019-02-18 20:48 ` Yu Zhao 2019-02-18 20:48 ` Yu Zhao 2019-02-19 4:09 ` Anshuman Khandual 2019-02-19 4:09 ` Anshuman Khandual 2019-02-18 23:13 ` [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Yu Zhao 2019-02-18 23:13 ` Yu Zhao 2019-02-18 23:13 ` [PATCH v2 2/3] arm64: mm: don't call page table ctors for init_mm Yu Zhao 2019-02-18 23:13 ` Yu Zhao 2019-02-26 15:13 ` Mark Rutland 2019-02-26 15:13 ` Mark Rutland 2019-03-09 3:52 ` Yu Zhao 2019-03-09 3:52 ` Yu Zhao 2019-02-18 23:13 ` [PATCH v2 3/3] arm64: mm: enable per pmd page table lock Yu Zhao 2019-02-18 23:13 ` Yu Zhao 2019-02-19 4:21 ` [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Anshuman Khandual 2019-02-19 4:21 ` Anshuman Khandual 2019-02-19 5:32 ` Yu Zhao 2019-02-19 5:32 ` Yu Zhao 2019-02-19 6:17 ` Anshuman Khandual [this message] 2019-02-19 6:17 ` Anshuman Khandual 2019-02-19 22:28 ` Yu Zhao 2019-02-19 22:28 ` Yu Zhao 2019-02-20 10:27 ` Anshuman Khandual 2019-02-20 10:27 ` Anshuman Khandual 2019-02-20 12:24 ` Matthew Wilcox 2019-02-20 12:24 ` Matthew Wilcox 2019-02-20 20:22 ` Yu Zhao 2019-02-20 20:22 ` Yu Zhao 2019-02-20 20:59 ` Matthew Wilcox 2019-02-20 20:59 ` Matthew Wilcox 2019-02-20 20:59 ` Matthew Wilcox 2019-02-20 1:34 ` Matthew Wilcox 2019-02-20 1:34 ` Matthew Wilcox 2019-02-20 1:34 ` Matthew Wilcox 2019-02-20 3:20 ` Anshuman Khandual 2019-02-20 3:20 ` Anshuman Khandual 2019-02-20 21:03 ` Matthew Wilcox 2019-02-20 21:03 ` Matthew Wilcox 2019-02-20 21:03 ` Matthew Wilcox 2019-02-26 15:12 ` Mark Rutland 2019-02-26 15:12 ` Mark Rutland 2019-03-09 4:01 ` Yu Zhao 2019-03-09 4:01 ` Yu Zhao 2019-03-09 4:01 ` Yu Zhao 2019-03-10 1:19 ` [PATCH v3 " Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-10 1:19 ` [PATCH v3 2/3] arm64: mm: don't call page table ctors for init_mm Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-10 1:19 ` [PATCH v3 3/3] arm64: mm: enable per pmd page table lock Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-10 1:19 ` Yu Zhao 2019-03-11 8:28 ` Anshuman Khandual 2019-03-11 8:28 ` Anshuman Khandual 2019-03-11 23:10 ` Yu Zhao 2019-03-11 23:10 ` Yu Zhao 2019-03-11 12:12 ` Mark Rutland 2019-03-11 12:12 ` Mark Rutland 2019-03-11 12:57 ` Anshuman Khandual 2019-03-11 12:57 ` Anshuman Khandual 2019-03-11 23:11 ` Yu Zhao 2019-03-11 23:11 ` Yu Zhao 2019-03-11 23:11 ` Yu Zhao 2019-03-11 7:45 ` [PATCH v3 1/3] arm64: mm: use appropriate ctors for page tables Anshuman Khandual 2019-03-11 7:45 ` Anshuman Khandual 2019-03-11 23:23 ` Yu Zhao 2019-03-11 23:23 ` Yu Zhao 2019-03-12 0:57 ` [PATCH v4 1/4] " Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` [PATCH v4 2/4] arm64: mm: don't call page table ctors for init_mm Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` [PATCH v4 3/4] arm64: mm: call ctor for stage2 pmd page Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 2:19 ` [PATCH] KVM: ARM: Remove pgtable page standard functions from stage-2 page tables Anshuman Khandual 2019-03-12 2:19 ` Anshuman Khandual 2019-03-12 2:40 ` Yu Zhao 2019-03-12 2:40 ` Yu Zhao 2019-03-12 10:37 ` Suzuki K Poulose 2019-03-12 10:37 ` Suzuki K Poulose 2019-03-12 11:31 ` Anshuman Khandual 2019-03-12 11:31 ` Anshuman Khandual 2019-03-12 11:43 ` Suzuki K Poulose 2019-03-12 11:43 ` Suzuki K Poulose 2019-03-12 13:25 ` [PATCH V2] " Anshuman Khandual 2019-03-12 13:25 ` Anshuman Khandual 2019-04-01 16:16 ` Will Deacon 2019-04-01 16:16 ` Will Deacon 2019-04-01 16:16 ` Will Deacon 2019-04-01 18:34 ` Yu Zhao 2019-04-01 18:34 ` Yu Zhao 2019-04-01 18:34 ` Yu Zhao 2019-04-02 9:03 ` Will Deacon 2019-04-02 9:03 ` Will Deacon 2019-04-02 9:03 ` Will Deacon 2019-04-08 14:22 ` Will Deacon 2019-04-08 14:22 ` Will Deacon 2019-04-08 14:22 ` Will Deacon 2019-04-08 14:22 ` Will Deacon 2019-04-08 17:18 ` Yu Zhao 2019-04-08 17:18 ` Yu Zhao 2019-04-08 17:18 ` Yu Zhao 2019-04-08 9:09 ` Marc Zyngier 2019-04-08 9:09 ` Marc Zyngier 2019-04-08 9:09 ` Marc Zyngier 2019-04-08 9:09 ` Marc Zyngier 2019-03-12 0:57 ` [PATCH v4 4/4] arm64: mm: enable per pmd page table lock Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-03-12 0:57 ` Yu Zhao 2019-02-19 3:08 ` [PATCH] " Anshuman Khandual 2019-02-19 3:08 ` Anshuman Khandual
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