Merge "mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT"

	  This feature collects and exposes statistics via debugfs. The

	  information includes global and per chunk statistics, which can

	  be used to help understand percpu memory usage.

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.