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    SubjectRe: [PATCH v2 6/7] x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
    Date
    On 26.02.21 13:04, Oscar Salvador wrote:
    > On Thu, Feb 25, 2021 at 07:29:07PM +0100, David Hildenbrand wrote:
    >> On 09.02.21 14:38, Oscar Salvador wrote:
    >>> Enable x86_64 platform to use the MHP_MEMMAP_ON_MEMORY feature.
    >>>
    >>> Signed-off-by: Oscar Salvador <osalvador@suse.de>
    >>> ---
    >>> arch/x86/Kconfig | 4 ++++
    >>> 1 file changed, 4 insertions(+)
    >>>
    >>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    >>> index 72663de8b04c..81046b7adb10 100644
    >>> --- a/arch/x86/Kconfig
    >>> +++ b/arch/x86/Kconfig
    >>> @@ -2440,6 +2440,10 @@ config ARCH_ENABLE_MEMORY_HOTREMOVE
    >>> def_bool y
    >>> depends on MEMORY_HOTPLUG
    >>> +config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
    >>> + def_bool y
    >>> + depends on X86_64 && MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP_ENABLE
    >>
    >> It depends on SPARSEMEM_VMEMMAP, no?
    >>
    >> I think we could have
    >>
    >> SPARSEMEM_VMEMMAP_ENABLE=y
    >> and
    >> SPARSEMEM_VMEMMAP=n
    >>
    >> on manually tuned configs.
    >
    > I do not think this can happen:
    >
    > from mm/Kconfig:
    >
    > config SPARSEMEM_VMEMMAP_ENABLE
    > bool
    >
    > config SPARSEMEM_VMEMMAP
    > bool "Sparse Memory virtual memmap"
    > depends on SPARSEMEM && SPARSEMEM_VMEMMAP_ENABLE
    > default y
    > help
    > SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise
    > pfn_to_page and page_to_pfn operations. This is the most
    > efficient option when sufficient kernel resources are available
    >
    > and from arch/x86/Kconfig:
    >
    > config ARCH_SPARSEMEM_ENABLE
    > def_bool y
    > depends on X86_64 || NUMA || X86_32 || X86_32_NON_STANDARD
    > select SPARSEMEM_STATIC if X86_32
    > select SPARSEMEM_VMEMMAP_ENABLE if X86_64
    >
    >
    > So, if I read this correctly, for SPARSEMEM_VMEMMAP to be true,
    > SPARSEMEM_VMEMMAP_ENABLE needs to be true as well.
    >
    > Am I missing something?

    Take your config and set
    X86_5LEVEL=n
    (because it enforces SPARSEMEM_VMEMMAP)
    and
    SPARSEMEM_VMEMMAP=n

    When compiling, you'll end up with a config like
    CONFIG_SPARSEMEM_VMEMMAP_ENABLE=y
    # CONFIG_SPARSEMEM_VMEMMAP is not set

    Yet, with your patch you would get

    ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE=y

    And it would not get fenced off in the code, right?


    I think you either have to check (IS_ENABLED(CONFIG_SPARSEMEM_VMEMMAP))
    in addition in your code, or enforce it differently. Like


    config MHP_MEMMAP_ON_MEMORY
    depends on SPARSEMEM_VMEMMAP && ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
    bool


    Then you can simplify the arch Kconfig settings, removing the sparesemem
    dependency there.

    --
    Thanks,

    David / dhildenb

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