Re: ZERO_PAGE refcounting causes cache line bouncing

[William Lee Irwin III <wli@holomorphy.com>]

On Mon, Mar 19, 2007 at 04:56:47PM +1100, Nick Piggin wrote:
> Yes, I have the patch to do it quite easily. Per-node ZERO_PAGE could be
> another option, but that's going to cost another page flag if we wish to
> recognise the zero page in wp faults like we do now (hmm, for some reason
> it is OK to special case it _there_).

No need for a page flag. A per-node array of struct page * can be used
to check by merely indexing into it with the nid of the page's node. e.g.

struct page *get_zero_page(int nid, unsigned long addr)
{
	return zero_pages[nid][(addr & SOME_ARCHDEP_MASK) >> PAGE_SHIFT];
}

/* any time we fish one out of a pte we have a uvaddr */
int is_zero_page_addr(struct page *page, unsigned long address)
{
	return page == get_zero_page(page_to_nid(page), address);
}


-- wli

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