On 05/17/2018 04:06 AM, 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, ARCH_HAS_PTE_SPECIAL, SMP and MMU.
> The architecture support is needed since the speculative page fault handler
> is called from the architecture's page faulting code, and some code has to
> be added there to handle the speculative handler.
> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page()
> does processing that is not compatible with the speculative handling in the
> case ARCH_HAS_PTE_SPECIAL is not set.
> Suggested-by: Thomas Gleixner <t...@linutronix.de>
> Suggested-by: David Rientjes <rient...@google.com>
> Signed-off-by: Laurent Dufour <lduf...@linux.vnet.ibm.com>
> mm/Kconfig | 22 ++++++++++++++++++++++
> 1 file changed, 22 insertions(+)
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 1d0888c5b97a..a38796276113 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -761,3 +761,25 @@ config GUP_BENCHMARK
> config ARCH_HAS_PTE_SPECIAL
> +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 ARCH_HAS_PTE_SPECIAL && 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
because 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
allocated, the speculative page fault fails and a classic page fault
> + is then tried.
Also, all of the help text (below the "help" line) should be indented by
1 tab + 2 spaces (in coding-style.rst).