the data struct of slab

struct kmem_cache {
// 可被调整缓存的参数，由 cache_chain_mutex 锁保护
	unsigned int batchcount;
	unsigned int limit; // 指定了 per-CPU 列表中保存的对象上限。如果超出，内核会将 batchcount 个对象返回到 slab
	unsigned int shared;

	unsigned int size; // 指定缓存管理区对象的长度
	u32 reciprocal_buffer_size; 

// 在每次分配和释放时访问
	unsigned int flags;		/* constant flags */
	unsigned int num;		/* # of objs per slab */

// cache 的伸缩
	/* order of pgs per slab (2^n) */
	unsigned int gfporder;

	/* force GFP flags, e.g. GFP_DMA */
	gfp_t allocflags;

	size_t colour;			/* cache 着色的范围 */
	unsigned int colour_off;	/* colour 着色的 offset */
	struct kmem_cache *slabp_cache;
	unsigned int slab_size;

	/* 构造函数 func */
	void (*ctor)(void *obj);

// cache 的构造或移除 
	const char *name; // cache 的名字
	struct list_head list;
	int refcount;
	int object_size;
	int align;

// debug 和统计信息不关注

// 每 cpu 每 内存节点的数据
	/* 
	 * We put array[] at the end of kmem_cache, because we want to size
	 * this array to nr_cpu_ids slots instead of NR_CPUS
	 * (see kmem_cache_init())
	 * We still use [NR_CPUS] and not [1] or [0] because cache_cache
	 * is statically defined, so we reserve the max number of cpus.
	 *
	 * We also need to guarantee that the list is able to accomodate a
	 * pointer for each node since "nodelists" uses the remainder of
	 * available pointers.
	 */
	struct kmem_cache_node **node; // ULK3 里面的 kmem_list3 结构体
	struct array_cache *array[NR_CPUS + MAX_NUMNODES]; // 数组指针，每一项对应 cpu 或 numa 节点
};

/*
 * The slab lists for all objects.
 */
struct kmem_cache_node {
	spinlock_t list_lock;

#ifdef CONFIG_SLAB
// slab 的三种分类，partial，full，free 组织链表
// partial 链表放在第一个性能更好一点
	struct list_head slabs_partial;
	struct list_head slabs_full;
	struct list_head slabs_free;
	unsigned long free_objects; // 所有未使用的对象
	unsigned int free_limit; // 指定了所有 slab 上容许未使用对象的最大数目
	unsigned int colour_next;	// 每节点的着色
	struct array_cache *shared;	// 指向所有 cpu 共享的本地 cache
	struct array_cache **alien;	// on other nodes
	unsigned long next_reap;	// 用于页框回收
	int free_touched;		// 用于 slab 分配器的页框回收
#endif

// 移除了部分不关注的信息
...
};

struct array_cache {
	unsigned int avail; // available 指向当前可用对象指针的数量
	unsigned int limit; // 缓存在收缩之后空闲对象数量上限
	unsigned int batchcount; // 在 per-CPU 列表为空的情况下，从 cache 的 slab 中获取对象的数目
	unsigned int touched; // 从 cache 移除时 touched 为 1，cache 收缩时则 0.
	spinlock_t lock;
	void *entry[]; /* 下面注释写的蛮清楚的       
			 * Must have this definition in here for the proper
			 * alignment of array_cache. Also simplifies accessing
			 * the entries.
			 *
			 * Entries should not be directly dereferenced as
			 * entries belonging to slabs marked pfmemalloc will
			 * have the lower bits set SLAB_OBJ_PFMEMALLOC
			 */
};

struct slab {
        union {
                struct {
                        struct list_head list; 
                        unsigned long colouroff; // 第一个 obj 的着色 offset
                        void *s_mem;            // 第一个 obj 的地址包含着色 offset
                        unsigned int inuse;     // 当前被用的 obj 的数量
                        kmem_bufctl_t free;
                        unsigned short nodeid;
                };
                struct slab_rcu __slab_cover_slab_rcu;
        };
};