Re: [RFC] Making compound pages mandatory

[Nick Piggin]

Nick Piggin wrote:
> Nick Piggin wrote:
>
> > Good idea. BTW, any reason why the following (very)micro optimisation
> > shouldn't go in?
> >
> > It currently only picks up a couple of things under fs/, but might help
> > reduce other ifdefery around the place. For example mm.h: page_count and
> > get_page.
>
> Like this, perhaps? It does actually introduce a change in the object
> code. Namely hugetlb's put_page will now also be done inline for non
> compound pages - maybe this change is unacceptable though, but it does
> cut down the ifdefs.

Err... attached.


---

 linux-2.6-npiggin/include/linux/mm.h |   20 ++++----------------
 linux-2.6-npiggin/mm/swap.c          |   20 +++++++-------------
 2 files changed, 11 insertions(+), 29 deletions(-)

diff -puN include/linux/mm.h~mm-less-ifdefs include/linux/mm.h
--- linux-2.6/include/linux/mm.h~mm-less-ifdefs	2004-11-17 14:14:12.000000000 +1100
+++ linux-2.6-npiggin/include/linux/mm.h	2004-11-17 14:17:24.000000000 +1100
@@ -288,11 +288,9 @@ struct page {
 
 extern void FASTCALL(__page_cache_release(struct page *));
 
-#ifdef CONFIG_HUGETLB_PAGE
-
 static inline int page_count(struct page *p)
 {
-	if (PageCompound(p))
+	if (unlikely(PageCompound(p)))
 		p = (struct page *)p->private;
 	return atomic_read(&(p)->_count) + 1;
 }
@@ -304,25 +302,15 @@ static inline void get_page(struct page 
 	atomic_inc(&page->_count);
 }
 
-void put_page(struct page *page);
-
-#else		/* CONFIG_HUGETLB_PAGE */
-
-#define page_count(p)		(atomic_read(&(p)->_count) + 1)
-
-static inline void get_page(struct page *page)
-{
-	atomic_inc(&page->_count);
-}
-
+void put_compound_page(struct page *page);
 static inline void put_page(struct page *page)
 {
+	if (unlikely(PageCompound(page)))
+		put_compound_page(page);
 	if (!PageReserved(page) && put_page_testzero(page))
 		__page_cache_release(page);
 }
 
-#endif		/* CONFIG_HUGETLB_PAGE */
-
 /*
  * Multiple processes may "see" the same page. E.g. for untouched
  * mappings of /dev/null, all processes see the same page full of
diff -puN mm/swap.c~mm-less-ifdefs mm/swap.c
--- linux-2.6/mm/swap.c~mm-less-ifdefs	2004-11-17 14:15:20.000000000 +1100
+++ linux-2.6-npiggin/mm/swap.c	2004-11-17 14:15:48.000000000 +1100
@@ -35,23 +35,17 @@
 int page_cluster;
 
 #ifdef CONFIG_HUGETLB_PAGE
-
-void put_page(struct page *page)
+void put_compound_page(struct page *page)
 {
-	if (unlikely(PageCompound(page))) {
-		page = (struct page *)page->private;
-		if (put_page_testzero(page)) {
-			void (*dtor)(struct page *page);
+	page = (struct page *)page->private;
+	if (put_page_testzero(page)) {
+		void (*dtor)(struct page *page);
 
-			dtor = (void (*)(struct page *))page[1].mapping;
-			(*dtor)(page);
-		}
-		return;
+		dtor = (void (*)(struct page *))page[1].mapping;
+		(*dtor)(page);
 	}
-	if (!PageReserved(page) && put_page_testzero(page))
-		__page_cache_release(page);
 }
-EXPORT_SYMBOL(put_page);
+EXPORT_SYMBOL(put_compound_page);
 #endif
 
 /*

_