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

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Date:   Fri, 9 Aug 2019 13:03:30 -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 2019-08-09 11:01 a.m., Greentime Hu wrote:
> Hi Logan,
> 
> Logan Gunthorpe <logang@...tatee.com> 於 2019年8月9日 週五 下午11:47寫道：
>>
>>
>>
>> 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.
>>
> 
> Thank you for point me out that. I just checked the generic
> implementation and I should use that one.
> Sorry I didn't check the generic one and just implement it again.
> I think the only patch we need is the first part to use generic
> pfn_valid(). I just tested it and yes it can boot successfully in dts
> with hole.
> 
> It will fail in this check ((pfn)-pfn_base) < max_mapnr.

Sounds to me like max_mapnr is not set correctly. See the code in
setup_bootmem(). Seems like 'mem_size' should be set to the largest
memory block, not just the one that contains the kernel...


> 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..80d28fa1e2eb 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -100,8 +100,10 @@ extern unsigned long min_low_pfn;
>  #define page_to_bus(page)      (page_to_phys(page))
>  #define phys_to_page(paddr)    (pfn_to_page(phys_to_pfn(paddr)))
> 
> +#if !defined(CONFIG_SPARSEMEM_VMEMMAP)
>  #define pfn_valid(pfn) \
>         (((pfn) >= pfn_base) && (((pfn)-pfn_base) < max_mapnr))
> +#endif
> 
>  #define ARCH_PFN_OFFSET                (pfn_base)


This patch still makes no sense. I'm not sure why we have an arch
specific pfn_valid() because it's very similar to the generic one. But
my guess is there's a reason for it and it's not doing what it is
supposed when you remove it for the sparsemem case.

Logan