Re: [PATCH v1 4/4] arm64: drop pfn_valid_within() and simplify pfn_valid()

David Hildenbrand
2021-04-20T16:01:06Z

On 20.04.21 11:09, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@linux.ibm.com>
>
> The arm64's version of pfn_valid() differs from the generic because of two
> reasons:
>
> * Parts of the memory map are freed during boot. This makes it necessary to
> verify that there is actual physical memory that corresponds to a pfn
> which is done by querying memblock.
>
> * There are NOMAP memory regions. These regions are not mapped in the
> linear map and until the previous commit the struct pages representing
> these areas had default values.
>
> As the consequence of absence of the special treatment of NOMAP regions in
> the memory map it was necessary to use memblock_is_map_memory() in
> pfn_valid() and to have pfn_valid_within() aliased to pfn_valid() so that
> generic mm functionality would not treat a NOMAP page as a normal page.
>
> Since the NOMAP regions are now marked as PageReserved(), pfn walkers and
> the rest of core mm will treat them as unusable memory and thus
> pfn_valid_within() is no longer required at all and can be disabled by
> removing CONFIG_HOLES_IN_ZONE on arm64.
>
> pfn_valid() can be slightly simplified by replacing
> memblock_is_map_memory() with memblock_is_memory().
>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> arch/arm64/Kconfig | 3 ---
> arch/arm64/mm/init.c | 4 ++--
> 2 files changed, 2 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index e4e1b6550115..58e439046d05 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1040,9 +1040,6 @@ config NEED_PER_CPU_EMBED_FIRST_CHUNK
> def_bool y
> depends on NUMA
>
> -config HOLES_IN_ZONE
> - def_bool y
> -
> source "kernel/Kconfig.hz"
>
> config ARCH_SPARSEMEM_ENABLE
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index c54e329aca15..370f33765b64 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -243,7 +243,7 @@ int pfn_valid(unsigned long pfn)
>
> /*
> * ZONE_DEVICE memory does not have the memblock entries.
> - * memblock_is_map_memory() check for ZONE_DEVICE based
> + * memblock_is_memory() check for ZONE_DEVICE based
> * addresses will always fail. Even the normal hotplugged
> * memory will never have MEMBLOCK_NOMAP flag set in their
> * memblock entries. Skip memblock search for all non early
> @@ -254,7 +254,7 @@ int pfn_valid(unsigned long pfn)
> return pfn_section_valid(ms, pfn);
> }
> #endif
> - return memblock_is_map_memory(addr);
> + return memblock_is_memory(addr);
> }
> EXPORT_SYMBOL(pfn_valid);
>
>

What are the steps needed to get rid of custom pfn_valid() completely?

I'd assume we would have to stop freeing parts of the mem map during
boot. How relevant is that for arm64 nowadays, especially with reduced
section sizes?

--
Thanks,

David / dhildenb