Variable Order Page Cache: Add functions to establish sizes

We use the macros PAGE_CACHE_SIZE PAGE_CACHE_SHIFT PAGE_CACHE_MASK
and PAGE_CACHE_ALIGN in various places in the kernel. These are now
the base page size but we do not have a means to calculating these
values for higher order pages.

Provide these functions. An address_space pointer must be passed
to them.

New function			Related base page constant
---------------------------------------------------
page_cache_shift(a)		PAGE_CACHE_SHIFT
page_cache_size(a)		PAGE_CACHE_SIZE
page_cache_mask(a)		PAGE_CACHE_MASK
page_cache_align(addr,a)	PAGE_CACHE_ALIGN(addr)

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
 include/linux/pagemap.h |   21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

Index: linux-2.6.21-rc7/include/linux/pagemap.h
===================================================================
--- linux-2.6.21-rc7.orig/include/linux/pagemap.h	2007-04-18 23:01:09.000000000 -0700
+++ linux-2.6.21-rc7/include/linux/pagemap.h	2007-04-18 23:03:32.000000000 -0700
@@ -49,6 +49,27 @@ static inline void mapping_set_gfp_mask(
 #define PAGE_CACHE_MASK		PAGE_MASK
 #define PAGE_CACHE_ALIGN(addr)	(((addr)+PAGE_CACHE_SIZE-1)&PAGE_CACHE_MASK)
 
+static inline int page_cache_shift(struct address_space *a)
+{
+	return a->order + PAGE_CACHE_SHIFT;
+}
+
+static inline unsigned long page_cache_size(struct address_space *a)
+{
+	return PAGE_CACHE_SIZE << a->order;
+}
+
+static inline unsigned long page_cache_mask(struct address_space *a)
+{
+	return PAGE_CACHE_MASK << a->order;
+}
+
+static inline unsigned long page_cache_align(unsigned long addr,
+		struct address_space *a)
+{
+	return (((addr) + page_cache_size(a) - 1) & page_cache_mask(a));
+}
+
 #define page_cache_get(page)		get_page(page)
 #define page_cache_release(page)	put_page(page)
 void release_pages(struct page **pages, int nr, int cold);