linux-kernel - Re: [PATCH v4 4/4] arm64: drop pfn_valid_within() and simplify pfn

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Date:   Tue, 11 May 2021 16:40:01 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        David Hildenbrand <david@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v4 4/4] arm64: drop pfn_valid_within() and simplify
 pfn_valid()

On Tue, 11 May 2021 13:05:50 +0300 Mike Rapoport <rppt@...nel.org> wrote:

> From: Mike Rapoport <rppt@...ux.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().
> 
> ...
>
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1052,9 +1052,6 @@ 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

https://lkml.kernel.org/r/20210417075946.181402-1-wangkefeng.wang@huawei.com
already did this, so I simply dropped that hunk?  And I don't think the
changelog needs updating for this?


> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index 798f74f501d5..fb07218da2c0 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -251,7 +251,7 @@ int pfn_valid(unsigned long pfn)
>  	if (!early_section(ms))
>  		return pfn_section_valid(ms, pfn);
>  
> -	return memblock_is_map_memory(addr);
> +	return memblock_is_memory(addr);
>  }
>  EXPORT_SYMBOL(pfn_valid);