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SubjectRe: [PATCH v10 01/25] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
Hi Laurent,

I guess it's good timing to review. Guess LSF/MM goes so might change
a lot since then. :) Anyway, I grap a time to review.

On Tue, Apr 17, 2018 at 04:33:07PM +0200, Laurent Dufour wrote:
> This configuration variable will be used to build the code needed to
> handle speculative page fault.
>
> By default it is turned off, and activated depending on architecture
> support, SMP and MMU.

Can we have description in here why it depends on architecture?

>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Suggested-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
> ---
> mm/Kconfig | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index d5004d82a1d6..5484dca11199 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -752,3 +752,25 @@ config GUP_BENCHMARK
> performance of get_user_pages_fast().
>
> See tools/testing/selftests/vm/gup_benchmark.c
> +
> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> + def_bool n
> +
> +config SPECULATIVE_PAGE_FAULT
> + bool "Speculative page faults"
> + default y
> + depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
> + depends on MMU && SMP
> + help
> + Try to handle user space page faults without holding the mmap_sem.
> +
> + This should allow better concurrency for massively threaded process
> + since the page fault handler will not wait for other threads memory
> + layout change to be done, assuming that this change is done in another
> + part of the process's memory space. This type of page fault is named
> + speculative page fault.
> +
> + If the speculative page fault fails because of a concurrency is
> + detected or because underlying PMD or PTE tables are not yet
> + allocating, it is failing its processing and a classic page fault
> + is then tried.
> --
> 2.7.4
>

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