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:

quoted

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