linux-kernel - Re: [PATCH v4 2/2] RISC-V: Implement sparsemem

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Date:   Tue, 13 Aug 2019 10:49:51 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Greentime Hu <green.hu@...il.com>, Rob Herring <robh@...nel.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andrew Waterman <andrew@...ive.com>,
        Palmer Dabbelt <palmer@...ive.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Stephen Bates <sbates@...thlin.com>,
        Olof Johansson <olof@...om.net>, greentime.hu@...ive.com,
        linux-riscv@...ts.infradead.org,
        Michael Clark <michaeljclark@....com>,
        Christoph Hellwig <hch@....de>, linux-mm@...r.kernel.org
Subject: Re: [PATCH v4 2/2] RISC-V: Implement sparsemem

On 2019-08-13 10:39 a.m., Paul Walmsley wrote:
> On Tue, 13 Aug 2019, Logan Gunthorpe wrote:
> 
>> On 2019-08-13 12:04 a.m., Greentime Hu wrote:
>>
>>> Every architecture with mmu defines their own pfn_valid().
>>
>> Not true. Arm64, for example just uses the generic implementation in
>> mmzone.h. 
> 
> arm64 seems to define their own:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/Kconfig#n899

Oh, yup. My mistake.

> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/mm/init.c#n235
> 
> While there are many architectures which have their own pfn_valid(); 
> oddly, almost none of them set HAVE_ARCH_PFN_VALID ?

Yes, much of this is super confusing. Seems HAVE_ARCH_PFN_VALID only
matters if SPARSEMEM is set. So risc-v probably doesn't need to set it
and we just need a #ifdef !CONFIG_FLATMEM around the pfn_valid
definition like other arches.

Logan