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

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Date:   Fri, 9 Aug 2019 09:46:49 -0600
From:   Logan Gunthorpe <logang@...tatee.com>
To:     Greentime Hu <green.hu@...il.com>
Cc:     greentime.hu@...ive.com, paul.walmsley@...ive.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>,
        Zong Li <zong@...estech.com>, Olof Johansson <olof@...om.net>,
        linux-riscv@...ts.infradead.org,
        Michael Clark <michaeljclark@....com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v4 2/2] RISC-V: Implement sparsemem



On 2019-08-08 10:23 p.m., Greentime Hu wrote:
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 3f12b069af1d..208b3e14ccd8 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -116,7 +116,8 @@ config PGTABLE_LEVELS
>         default 2
> 
>  config HAVE_ARCH_PFN_VALID
> -       def_bool y
> +       bool
> +       default !SPARSEMEM_VMEMMAP
> 
>  menu "Platform type"
> 
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 8ddb6c7fedac..6991f7a5a4a7 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -93,16 +93,20 @@ extern unsigned long min_low_pfn;
>  #define virt_to_pfn(vaddr)     (phys_to_pfn(__pa(vaddr)))
>  #define pfn_to_virt(pfn)       (__va(pfn_to_phys(pfn)))
> 
> +#if !defined(CONFIG_SPARSEMEM_VMEMMAP)
> +#define pfn_valid(pfn) \
> +       (((pfn) >= pfn_base) && (((pfn)-pfn_base) < max_mapnr))
>  #define virt_to_page(vaddr)    (pfn_to_page(virt_to_pfn(vaddr)))
>  #define page_to_virt(page)     (pfn_to_virt(page_to_pfn(page)))
> +#else
> +#define virt_to_page(vaddr)    ((struct page *)((((u64)vaddr -
> va_pa_offset) / PAGE_SIZE) * sizeof(struct page) + VMEMMAP_START))
> +#define page_to_virt(pg)       ((void *)(((((u64)pg - VMEMMAP_START) /
> sizeof(struct page)) * PAGE_SIZE) + va_pa_offset))
> +#endif

This doesn't make sense to me at all. It should always use pfn_to_page()
for virt_to_page() and the generic pfn_to_page()/page_to_pfn()
implementations essentially already do what you are doing in a cleaner
way. So I'd be really surprised if this does anything at all.

Logan