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[217.140.101.70]) by mx.google.com with ESMTP id m26si200120ejr.19.2019.03.11.01.28.40 for ; Mon, 11 Mar 2019 01:28:40 -0700 (PDT) Received-SPF: pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.101.70 as permitted sender) client-ip=217.140.101.70; Authentication-Results: mx.google.com; spf=pass (google.com: domain of anshuman.khandual@arm.com designates 217.140.101.70 as permitted sender) smtp.mailfrom=anshuman.khandual@arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9D338A78; Mon, 11 Mar 2019 01:28:39 -0700 (PDT) Received: from [10.163.1.86] (unknown [10.163.1.86]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C16FD3F59C; Mon, 11 Mar 2019 01:28:30 -0700 (PDT) Subject: Re: [PATCH v3 3/3] arm64: mm: enable per pmd page table lock To: Yu Zhao , Catalin Marinas , Will Deacon , Mark Rutland Cc: "Aneesh Kumar K . V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Joel Fernandes , "Kirill A . Shutemov" , Ard Biesheuvel , Chintan Pandya , Jun Yao , Laura Abbott , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org References: <20190218231319.178224-1-yuzhao@google.com> <20190310011906.254635-1-yuzhao@google.com> <20190310011906.254635-3-yuzhao@google.com> From: Anshuman Khandual Message-ID: Date: Mon, 11 Mar 2019 13:58:27 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190310011906.254635-3-yuzhao@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03/10/2019 06:49 AM, Yu Zhao wrote: > Switch from per mm_struct to per pmd page table lock by enabling > ARCH_ENABLE_SPLIT_PMD_PTLOCK. This provides better granularity for > large system. > > I'm not sure if there is contention on mm->page_table_lock. Given > the option comes at no cost (apart from initializing more spin > locks), why not enable it now. > > We only do so when pmd is not folded, so we don't mistakenly call > pgtable_pmd_page_ctor() on pud or p4d in pgd_pgtable_alloc(). (We > check shift against PMD_SHIFT, which is same as PUD_SHIFT when pmd > is folded). > > Signed-off-by: Yu Zhao > --- > arch/arm64/Kconfig | 3 +++ > arch/arm64/include/asm/pgalloc.h | 12 +++++++++++- > arch/arm64/include/asm/tlb.h | 5 ++++- > 3 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index cfbf307d6dc4..a3b1b789f766 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -872,6 +872,9 @@ config ARCH_WANT_HUGE_PMD_SHARE > config ARCH_HAS_CACHE_LINE_SIZE > def_bool y > > +config ARCH_ENABLE_SPLIT_PMD_PTLOCK > + def_bool y if PGTABLE_LEVELS > 2 > + > config SECCOMP > bool "Enable seccomp to safely compute untrusted bytecode" > ---help--- > diff --git a/arch/arm64/include/asm/pgalloc.h b/arch/arm64/include/asm/pgalloc.h > index 52fa47c73bf0..dabba4b2c61f 100644 > --- a/arch/arm64/include/asm/pgalloc.h > +++ b/arch/arm64/include/asm/pgalloc.h > @@ -33,12 +33,22 @@ > > static inline pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long addr) > { > - return (pmd_t *)__get_free_page(PGALLOC_GFP); > + struct page *page; > + > + page = alloc_page(PGALLOC_GFP); > + if (!page) > + return NULL; > + if (!pgtable_pmd_page_ctor(page)) { > + __free_page(page); > + return NULL; > + } > + return page_address(page); > } > > static inline void pmd_free(struct mm_struct *mm, pmd_t *pmdp) > { > BUG_ON((unsigned long)pmdp & (PAGE_SIZE-1)); > + pgtable_pmd_page_dtor(virt_to_page(pmdp)); > free_page((unsigned long)pmdp); > } There is just one problem here. ARM KVM's stage2_pmd_free() calls into pmd_free() on a page originally allocated with __get_free_page() and never went through pgtable_pmd_page_ctor(). So when ARCH_ENABLE_SPLIT_PMD_PTLOCK is enabled stage2_pmd_free() pgtable_pmd_page_dtor() ptlock_free() kmem_cache_free(page_ptl_cachep, page->ptl) Though SLUB implementation for kmem_cache_free() seems to be handling NULL page->ptl (as the page never got it's lock allocated or initialized) correctly I am not sure if it is a right thing to do.