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SubjectRe: Re : Re : sparsemem usage
moreau francis wrote:
> Alan Cox wrote:
>> Mapping out parts of a section is quite normal - think about the 640K to
>> 1Mb hole in PC memory space.
> OK. But I'm still worry. Please consider the following code
> for (...; ...; ...) {
> [...]
> if (pfn_valid(i))
> num_physpages++;
> [...]
> }
> In that case num_physpages won't store an accurate value. Still it will be
> used by the kernel to make some statistic assumptions on other kernel
> data structure sizes.

That would be incorrect usage. pfn_valid() simply doesn't tell you if
you have memory backing a pfn, it mearly means you can interrogate the
page* for it. A good example of code which counts pages in a region is
in count_highmem_pages() which has a form as below:

for (pfn = start; pfn < end; pfn++) {
if (!pfn_valid(pfn))
page = pfn_to_page(pfn);
if (PageReserved(page))

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