On 17/05/2018 18:36, Randy Dunlap wrote: > Hi, > > 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 <tglx@xxxxxxxxxxxxx> >> Suggested-by: David Rientjes <rientjes@xxxxxxxxxx> >> Signed-off-by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx> >> --- >> 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 >> bool >> + >> +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 > > processes > >> + since the page fault handler will not wait for other threads memory > > thread's > >> + 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). Thanks, Randy for reviewing my miserable English grammar. I'll fix that and the indentation.
