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SubjectRe: [PATCH 1/1] mm: move FAULT_AROUND_ORDER to arch/
On Tue, Mar 25, 2014 at 12:20:15PM +0530, Madhavan Srinivasan wrote:
> Kirill A. Shutemov with the commit 96bacfe542 introduced
> vm_ops->map_pages() for mapping easy accessible pages around
> fault address in hope to reduce number of minor page faults.
> Based on his workload runs, suggested FAULT_AROUND_ORDER
> (knob to control the numbers of pages to map) is 4.
>
> This patch moves the FAULT_AROUND_ORDER macro to arch/ for
> architecture maintainers to decide on suitable FAULT_AROUND_ORDER
> value based on performance data for that architecture.
>
> Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
> ---
> arch/powerpc/include/asm/pgtable.h | 6 ++++++
> arch/x86/include/asm/pgtable.h | 5 +++++
> include/asm-generic/pgtable.h | 10 ++++++++++
> mm/memory.c | 2 --
> 4 files changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 3ebb188..9fcbd48 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -19,6 +19,12 @@ struct mm_struct;
> #endif
>
> /*
> + * With a few real world workloads that were run,
> + * the performance data showed that a value of 3 is more advantageous.
> + */
> +#define FAULT_AROUND_ORDER 3
> +
> +/*
> * We save the slot number & secondary bit in the second half of the
> * PTE page. We use the 8 bytes per each pte entry.
> */
> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 938ef1d..8387a65 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -7,6 +7,11 @@
> #include <asm/pgtable_types.h>
>
> /*
> + * Based on Kirill's test results, fault around order is set to 4
> + */
> +#define FAULT_AROUND_ORDER 4
> +
> +/*
> * Macro to mark a page protection value as UC-
> */
> #define pgprot_noncached(prot) \
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 1ec08c1..62f7f07 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -7,6 +7,16 @@
> #include <linux/mm_types.h>
> #include <linux/bug.h>
>
> +
> +/*
> + * Fault around order is a control knob to decide the fault around pages.
> + * Default value is set to 0UL (disabled), but the arch can override it as
> + * desired.
> + */
> +#ifndef FAULT_AROUND_ORDER
> +#define FAULT_AROUND_ORDER 0UL
> +#endif

FAULT_AROUND_ORDER == 0 case should be handled separately in
do_read_fault(): no reason to go to do_fault_around() if we are going to
fault in only one page.

--
Kirill A. Shutemov


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