From: Mark Rutland <mark.rutland@arm.com>
To: Yu Zhao <yuzhao@google.com>,
Anshuman Khandual <anshuman.khandual@arm.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>,
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
Subject: Re: [PATCH v3 3/3] arm64: mm: enable per pmd page table lock
Date: Mon, 11 Mar 2019 12:12:28 +0000 [thread overview]
Message-ID: <20190311121147.GA23361@lakrids.cambridge.arm.com> (raw)
In-Reply-To: <20190310011906.254635-3-yuzhao@google.com>
Hi,
On Sat, Mar 09, 2019 at 06:19:06PM -0700, 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).
Just to check, I take it pgtable_pmd_page_ctor() is now a NOP when the
PMD is folded, and this last paragraph is stale?
> Signed-off-by: Yu Zhao <yuzhao@google.com>
> ---
> 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);
> }
It looks like arm64's existing stage-2 code is inconsistent across
alloc/free, and IIUC this change might turn that into a real problem.
Currently we allocate all levels of stage-2 table with
__get_free_page(), but free them with p?d_free(). We always miss the
ctor and always use the dtor.
Other than that, this patch looks fine to me, but I'd feel more
comfortable if we could first fix the stage-2 code to free those stage-2
tables without invoking the dtor.
Anshuman, IIRC you had a patch to fix the stage-2 code to not invoke the
dtors. If so, could you please post that so that we could take it as a
preparatory patch for this series?
Thanks,
Mark.
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index 106fdc951b6e..4e3becfed387 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -62,7 +62,10 @@ static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
> static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
> unsigned long addr)
> {
> - tlb_remove_table(tlb, virt_to_page(pmdp));
> + struct page *page = virt_to_page(pmdp);
> +
> + pgtable_pmd_page_dtor(page);
> + tlb_remove_table(tlb, page);
> }
> #endif
>
> --
> 2.21.0.360.g471c308f928-goog
>
next prev parent reply other threads:[~2019-03-11 12:12 UTC|newest]
Thread overview: 38+ 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
2019-02-18 15:12 ` Will Deacon
2019-02-18 19:49 ` Yu Zhao
2019-02-18 20:48 ` Yu Zhao
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 ` [PATCH v2 2/3] arm64: mm: don't call page table ctors for init_mm Yu Zhao
2019-02-26 15:13 ` Mark Rutland
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
2019-02-19 4:21 ` [PATCH v2 1/3] arm64: mm: use appropriate ctors for page tables Anshuman Khandual
2019-02-19 5:32 ` Yu Zhao
2019-02-19 6:17 ` Anshuman Khandual
2019-02-19 22:28 ` Yu Zhao
2019-02-20 10:27 ` Anshuman Khandual
2019-02-20 12:24 ` Matthew Wilcox
2019-02-20 20:22 ` Yu Zhao
2019-02-20 20:59 ` Matthew Wilcox
2019-02-20 1:34 ` Matthew Wilcox
2019-02-20 3:20 ` Anshuman Khandual
2019-02-20 21:03 ` Matthew Wilcox
2019-02-26 15:12 ` Mark Rutland
2019-03-09 4:01 ` Yu Zhao
2019-03-10 1:19 ` [PATCH v3 " 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 ` [PATCH v3 3/3] arm64: mm: enable per pmd page table lock Yu Zhao
2019-03-11 8:28 ` Anshuman Khandual
2019-03-11 23:10 ` Yu Zhao
2019-03-11 12:12 ` Mark Rutland [this message]
2019-03-11 12:57 ` Anshuman Khandual
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 23:23 ` Yu Zhao
2019-03-12 0:57 ` [PATCH v4 1/4] " 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 ` [PATCH v4 3/4] arm64: mm: call ctor for stage2 pmd page Yu Zhao
2019-03-12 0:57 ` [PATCH v4 4/4] arm64: mm: enable per pmd page table lock Yu Zhao
2019-02-19 3:08 ` [PATCH] " Anshuman Khandual
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