lkml.org 
[lkml]   [2019]   [Apr]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v12 01/31] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
    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@linutronix.de>
    > Suggested-by: David Rientjes <rientjes@google.com>
    > Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>

    Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

    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
    >

    \
     
     \ /
      Last update: 2019-04-18 23:48    [W:4.146 / U:0.048 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site