Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
From: Randy Dunlap <hidden>
Date: 2018-05-17 16:36:20
Also in:
linuxppc-dev, lkml
Hi, On 05/17/2018 04:06 AM, Laurent Dufour wrote:
quoted hunk ↗ jump to hunk
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 <redacted> Suggested-by: David Rientjes <rientjes@google.com> Signed-off-by: Laurent Dufour <redacted> --- 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). -- ~Randy