Re: [PATCH] Optimize out pte_chain take two

[Andrew Morton <akpm@zip.com.au>]

Dave McCracken wrote:
> 
> Here's a version of my pte_chain removal patch that does not use anonymous
> unions, so it'll compile with gcc 2.95.  Once again, it's based on Rik's
> rmap-2.5.25-akpmtested.

Seems sane and simple, thanks.

This bit is icky:

+       union {
+               struct pte_chain * _pte_chain;  /* Reverse pte mapping pointer.
                                         * protected by PG_chainlock */
+               pte_t            * _pte_direct;
+       } _pte_union;
...
+
+#define        pte__chain      _pte_union._pte_chain
+#define        pte_direct      _pte_union._pte_direct


You could instead make it just a void * and have:

static inline struct pte_chain *page_pte_chain(struct page *page)
{
#ifdef DEBUG_RMAP
	BUG_ON(PageDirect(page));
#endif
	return page->rmap_thingy;
}

static inline pte_t *page_pte_direct(struct page *page)
{
#ifdef DEBUG_RMAP
	BUG_ON(!PageDirect(page));
#endif
	return page->rmap_thingy;
}

static inline void
set_page_pte_chain(struct page *page, struct pte_chain *pte_chain)
{
#ifdef DEBUG_RMAP
	BUG_ON(PageDirect(page));
#endif
	page->rmap_thingy = pte_chain;
}

static inline void
set_page_pte_direct(struct page *page, pte_t *ptep)
{
#ifdef DEBUG_RMAP
	BUG_ON(!PageDirect(page));
#endif
	page->rmap_thingy = ptep;
}

I think it's neater.  But then, I'm a convicted C++ weenie.

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