[PATCH -mm 4/6] slqb: record slab's start address in slqb_page

[Lai Jiangshan <laijs@cn.fujitsu.com>]

slqb's slab is coloring, it's will be useful that record the
color value or start address in struct slqb_page.

This fix adds a field in struct slqb_page to record slab's
start address, It will be used by kfree_rcu().


struct slqb_page has a field:
	struct kmem_cache_list *list;

the corresponding field in struct page is:

	union {
	    struct {
		unsigned long private;
		struct address_space *mapping;
	    };
	    struct kmem_cache *slab;
	    struct page *first_page;
	};

It's large than 'struct kmem_cache_list *list;'
*So we are safe to add a field in struct page.*


(This field will not become a burden in future:)
struct page is very small, this fix uses the last room of
struct page. But if we have to add a more important
field in struct slqb_page in future, We can record slab's
color value in slqb_page instead of start address.
like this:
	struct {
		unsigned long	flags;
		atomic_t	_count;
		u16		inuse;		/* use u16 instead */
		u16		color;  	/* of unsigned int */
		void 		*a_more_important_field;
		struct kmem_cache_list *list;
		void		 **freelist;
		union {
			struct list_head lru;
			struct rcu_head rcu_head;
		};
	};

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/mm/slqb.c b/mm/slqb.c
index 48bdf3b..c258ddc 100644
--- a/mm/slqb.c
+++ b/mm/slqb.c
@@ -41,6 +41,7 @@ struct slqb_page {
 			unsigned long	flags;		/* mandatory */
 			atomic_t	_count;		/* mandatory */
 			unsigned int	inuse;		/* Nr of objects */
+			void 		*s_mem;		/* start address */
 			struct kmem_cache_list *list;	/* Pointer to list */
 			void		 **freelist;	/* LIFO freelist */
 			union {
@@ -1010,6 +1011,7 @@ static struct slqb_page *new_slab_page(struct kmem_cache *s,
 	}
 	set_freepointer(s, last, NULL);
 
+	page->s_mem = start;
 	page->freelist = start;
 	page->inuse = 0;
 out: