Re : Re : Re : sparsemem usage

From: moreau francis
Date: Thu Aug 03 2006 - 08:50:50 EST

Andy Whitcroft wrote:
> 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))
> continue;
> page = pfn_to_page(pfn);
> if (PageReserved(page))
> continue;
> num_physpages++;
> }
num_physpages would still not give the right total number of pages in the
system. It will report a value smaller than the size of all memories which can
be suprising, depending on how it is used. In my mind I thought that it should
store the number of all pages in the system (reserved + free + ...).

Futhermore for flatmem model, my example that count the number of physical
pages is valid: reserved pages are really pages that are in used by the kernel.
But it's not valid anymore for sparsemem model. For consistency and code
sharing, I would make the same meaning of pfn_valid() and PageReserved() for
both models.


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