Date:   Mon, 12 Aug 2019 12:01:49 +0800
From:   Greentime Hu <green.hu@...il.com>
To:     Logan Gunthorpe <logang@...tatee.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

Hi Logan,

Logan Gunthorpe <logang@...tatee.com> 於 2019年8月10日 週六 上午3:03寫道：
>
>
>
> 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.

It will use another pfn_valid() implementation in
include/linux/mmzone.h if CONFIG_SPARSEMEM and
!CONFIG_HAVE_ARCH_PFN_VALID
It will be this one.

static inline int pfn_valid(unsigned long pfn)
{
        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
                return 0;
        return valid_section(__nr_to_section(pfn_to_section_nr(pfn)));
}

This generic pfn_valid() API can check the pfn is valid or not even if
there a hole in the memory.
For example:
A hole is between 0x100000000 to 0x180000000 (4GB-6GB) in my dts test case.

[    0.000000] In setup_bootmem, pfn_valid(0x180000)=1
[    0.000000] In setup_bootmem, pfn_valid(0x80000)=1
[    0.000000] In setup_bootmem, pfn_valid(0x80200)=1
[    0.000000] In setup_bootmem, pfn_valid(0x80300)=1
[    0.000000] In setup_bootmem, pfn_valid(0x160000)=0
[    0.000000] In setup_bootmem, pfn_valid(0x17ffff)=0
[    0.000000] In setup_bootmem, pfn_valid(0x120000)=0
[    0.000000] In setup_bootmem, pfn_valid(0x100000)=0
[    0.000000] In setup_bootmem, pfn_valid(0xfffff)=1

This generic pfn_valid() could tell the pfn is valid or not.


I think this one is only available for flatmem.
#define pfn_valid(pfn)  (((pfn) >= pfn_base) && (((pfn)-pfn_base) < max_mapnr))

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