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

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Date:   Sat, 10 Aug 2019 01:01:50 +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.
In my test case it will be
((6GB>>PAGE_SHIFT)-(2GB>>PAGE_SHIFT)=(4GB>>PAGE_SHIFT) <
(3GB>>PAGE_SHIFT) to return false.
 memory@...00000 {
         device_type = "memory";
         reg = <0x0 0x80000000 0x0 0x80000000>;
 };
 memory@...000000 {
         device_type = "memory";
         reg = <0x1 0x80000000 0x0 0x40000000>;
 };

To cause the check here failed to initialize page struct.

for (pfn = start_pfn; pfn < end_pfn; pfn++) {
        /*
         * There can be holes in boot-time mem_map[]s handed to this
         * function.  They do not exist on hotplugged memory.
         */
        if (context == MEMMAP_EARLY) {
                if (!early_pfn_valid(pfn))
                        continue;
                if (!early_pfn_in_nid(pfn, nid))
                        continue;
                if (overlap_memmap_init(zone, &pfn))
                        continue;
                if (defer_init(nid, pfn, end_pfn))
                        break;
        }

        page = pfn_to_page(pfn);
        __init_single_page(page, pfn, zone, nid);


------------------------------------------------------------------------------

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)