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SubjectRe: [RFC] Making compound pages mandatory
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

/*
_
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