[RFC] Common code 02/12] [slab]: Use page struct fields instead of casting

[Christoph Lameter <cl@linux.com>]

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Add fields to the page struct so that it is properly documented that
slab overlays the lru fields.

This cleans up some casts in slab.

Reviewed-by: Glauber Costa <glommer@parallels.com>
Signed-off-by: Christoph Lameter <cl@linux.com>

---
 include/linux/mm_types.h |    4 ++++
 mm/slab.c                |    8 ++++----
 2 files changed, 8 insertions(+), 4 deletions(-)

Index: linux-2.6/mm/slab.c
===================================================================
--- linux-2.6.orig/mm/slab.c	2012-05-15 09:59:03.385256611 -0500
+++ linux-2.6/mm/slab.c	2012-05-16 04:39:08.435864090 -0500
@@ -496,25 +496,25 @@ static bool slab_max_order_set __initdat
  */
 static inline void page_set_cache(struct page *page, struct kmem_cache *cache)
 {
-	page->lru.next = (struct list_head *)cache;
+	page->slab_cache = cache;
 }
 
 static inline struct kmem_cache *page_get_cache(struct page *page)
 {
 	page = compound_head(page);
 	BUG_ON(!PageSlab(page));
-	return (struct kmem_cache *)page->lru.next;
+	return page->slab_cache;
 }
 
 static inline void page_set_slab(struct page *page, struct slab *slab)
 {
-	page->lru.prev = (struct list_head *)slab;
+	page->slab_page = slab;
 }
 
 static inline struct slab *page_get_slab(struct page *page)
 {
 	BUG_ON(!PageSlab(page));
-	return (struct slab *)page->lru.prev;
+	return page->slab_page;
 }
 
 static inline struct kmem_cache *virt_to_cache(const void *obj)
Index: linux-2.6/include/linux/mm_types.h
===================================================================
--- linux-2.6.orig/include/linux/mm_types.h	2012-05-16 04:39:04.671864156 -0500
+++ linux-2.6/include/linux/mm_types.h	2012-05-16 04:39:08.435864090 -0500
@@ -108,6 +108,10 @@ struct page {
 			short int pobjects;
 #endif
 		};
+		struct {		/* SLAB */
+			struct kmem_cache *slab_cache;
+			struct slab *slab_page;
+		};
 	};
 
 	/* Remainder is not double word aligned */

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