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    SubjectRe: [PATCH] ARM: mm: Regarding section when dealing with meminfo
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    On Thu, 2011-01-20 at 23:28 +0900, Minchan Kim wrote:
    > On Thu, Jan 20, 2011 at 06:45:39PM +0900, KyongHo Cho wrote:
    > > Sparsemem allows that a bank of memory spans over several adjacent
    > > sections if the start address and the end address of the bank
    > > belong to different sections.
    > > When gathering statictics of physical memory in mem_init() and
    > > show_mem(), this possiblity was not considered.
    >
    > Please write down the result if we doesn't consider this patch.
    > I can understand what happens but for making good description and review,
    > merging easily, it would be better to write down the result without
    > the patch explicitly.

    You'll oops. __section_mem_map_addr() in:

    > #define __pfn_to_page(pfn) \
    > ({ unsigned long __pfn = (pfn); \
    > struct mem_section *__sec = __pfn_to_section(__pfn); \
    > __section_mem_map_addr(__sec) + __pfn; \
    > })

    will return NULL, you'll add some fuzz on to it with __pfn, then you'll
    oops when the arm show_mem() does PageReserved() and dereferences
    page->flags.

    Ether that, or with the sparsemem vmemmap variant, you'll get a
    valid-looking pointer with no backing memory, and oops as well.

    -- Dave



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