[Devel] [PATCH RHEL7 COMMIT] ms/mm: select HAVE_MOVE_PMD on x86 for faster mremap

Konstantin Khorenko khorenko at virtuozzo.com
Thu Jan 10 14:10:04 MSK 2019

The commit is pushed to "branch-rh7-3.10.0-957.1.3.vz7.83.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.1.3.vz7.83.4
commit d2a46b09c31cd9bcb362bc03f31cb8162ed4eeea
Author: Joel Fernandes (Google) <joel at joelfernandes.org>
Date:   Thu Jan 3 15:28:41 2019 -0800

    ms/mm: select HAVE_MOVE_PMD on x86 for faster mremap
    Moving page-tables at the PMD-level on x86 is known to be safe.  Enable
    this option so that we can do fast mremap when possible.
    Link: http://lkml.kernel.org/r/20181108181201.88826-4-joelaf@google.com
    Signed-off-by: Joel Fernandes (Google) <joel at joelfernandes.org>
    Suggested-by: Kirill A. Shutemov <kirill at shutemov.name>
    Acked-by: Kirill A. Shutemov <kirill at shutemov.name>
    Cc: Julia Lawall <Julia.Lawall at lip6.fr>
    Cc: Michal Hocko <mhocko at kernel.org>
    Cc: William Kucharski <william.kucharski at oracle.com>
    Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
    (cherry picked from commit 9f132f7e145506efc0744426cb338b18a54afc3b)
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    Patchset description:
    Patch "mm: speed up mremap by 20x on large regions" introduces
    optimization: when a moved region has source and destination addresses
    and size equal to multiple of PMD_SIZE; PTEs are not really copyed.
    Instead of this, new PMD pointer is changed to point to old PTEs, while
    old PMD is cleared.
    This may be useful, when CRIU remaps large memory areas on restore (but
    really, alignment to PMD_SIZE is not very often, though possible).
 arch/x86/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 35add8085a41..0534a73f379f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -35,6 +35,7 @@ config X86
 	select ARCH_SUPPORTS_INT128 if X86_64
 	select HAVE_IDE
+	select HAVE_MOVE_PMD

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