[PATCH] Tight check of pfn_valid on sparsemem - v4

[Christoph Lameter]

On Tue, 27 Jul 2010, Minchan Kim wrote:

> This patch registers address of mem_section to memmap itself's page struct's
> pg->private field. This means the page is used for memmap of the section.
> Otherwise, the page is used for other purpose and memmap has a hole.

What if page->private just happens to be the value of the page struct?
Even if that is not possible today, someday someone may add new
functionality to the kernel where page->pivage == page is used for some
reason.

Checking for PG_reserved wont work?

> +void mark_valid_memmap(unsigned long start, unsigned long end);
> +
> +#ifdef CONFIG_ARCH_HAS_HOLES_MEMORYMODEL
> +static inline int memmap_valid(unsigned long pfn)
> +{
> +	struct page *page = pfn_to_page(pfn);
> +	struct page *__pg = virt_to_page(page);
> +	return page_private(__pg) == (unsigned long)__pg;

Hmmm.. hmmm....