On Tue, Apr 16, 2019 at 03:44:52PM +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, 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@xxxxxxxxxxxxx> Reviewed-by: Jérôme Glisse <jglisse@xxxxxxxxxx> Small question below > --- > mm/Kconfig | 22 ++++++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/mm/Kconfig b/mm/Kconfig > index 0eada3f818fa..ff278ac9978a 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -761,4 +761,26 @@ 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 processes Is there any case where it does not provide better concurrency ? The should make me wonder :) > + since the page fault handler will not wait for other thread's 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 a concurrent modification > + is detected or because underlying PMD or PTE tables are not yet > + allocated, the speculative page fault fails and a classic page fault > + is then tried. > + > endmenu > -- > 2.21.0 >
