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    SubjectRe: [PATCH 2/2] arm64: mm: enable CONFIG_HOLES_IN_ZONE for NUMA
    On 4 January 2017 at 13:28, Will Deacon <will.deacon@arm.com> wrote:
    > On Wed, Dec 14, 2016 at 09:11:47AM +0000, Ard Biesheuvel wrote:
    >> The NUMA code may get confused by the presence of NOMAP regions within
    >> zones, resulting in spurious BUG() checks where the node id deviates
    >> from the containing zone's node id.
    >>
    >> Since the kernel has no business reasoning about node ids of pages it
    >> does not own in the first place, enable CONFIG_HOLES_IN_ZONE to ensure
    >> that such pages are disregarded.
    >>
    >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    >> ---
    >> arch/arm64/Kconfig | 4 ++++
    >> 1 file changed, 4 insertions(+)
    >>
    >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
    >> index 111742126897..0472afe64d55 100644
    >> --- a/arch/arm64/Kconfig
    >> +++ b/arch/arm64/Kconfig
    >> @@ -614,6 +614,10 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
    >> def_bool y
    >> depends on NUMA
    >>
    >> +config HOLES_IN_ZONE
    >> + def_bool y
    >> + depends on NUMA
    >> +
    >> source kernel/Kconfig.preempt
    >> source kernel/Kconfig.hz
    >
    > I'm happy to apply this, but I'll hold off until the first patch is queued
    > somewhere, since this doesn't help without the VM_BUG_ON being moved.
    >
    > Alternatively, I can queue both if somebody from the mm camp acks the
    > first patch.
    >

    Actually, I am not convinced the discussion is finalized. These
    patches do fix the issue, but Robert also suggested an alternative fix
    which may be preferable.

    http://marc.info/?l=linux-arm-kernel&m=148190753510107&w=2

    I haven't responded to it yet, due to the holidays, but I'd like to
    explore that solution a bit further before applying anything, if you
    don't mind.

    Thanks,
    Ard.

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