总结完了slab创建、对象分配、对象释放，在这里再看看slab的销毁。销毁slab很简单，由函数slab_destroy()实现。

/**
 * slab_destroy - destroy and release all objects in a slab
 * @cachep: cache pointer being destroyed
 * @slabp: slab pointer being destroyed
 *
 * Destroy all the objs in a slab, and release the mem back to the system.
 * Before calling the slab must have been unlinked from the cache.  The
 * cache-lock is not held/needed.
 */
 /*销毁slab，需要释放slab管理对象和slab对象。*/
static void slab_destroy(struct kmem_cache *cachep, struct slab *slabp)
{
	/* 获得slab首页面的虚拟地址 */
	void *addr = slabp->s_mem - slabp->colouroff;
	/*调试用*/
	slab_destroy_debugcheck(cachep, slabp);
	if (unlikely(cachep->flags & SLAB_DESTROY_BY_RCU)) {
		 /* rcu方式释放，暂时不做分析，主要是做并行优化 */
		struct slab_rcu *slab_rcu;

		slab_rcu = (struct slab_rcu *)slabp;
		slab_rcu->cachep = cachep;
		slab_rcu->addr = addr;
		call_rcu(&slab_rcu->head, kmem_rcu_free);
	} else {
		/* 释放slab占用的页面到伙伴系统中。如果是内置式，
		slab管理对象和slab对象在一起，可以同时释放。*/
		kmem_freepages(cachep, addr);
	 	/* 外置式，还需释放slab管理对象 */
		if (OFF_SLAB(cachep))
			kmem_cache_free(cachep->slabp_cache, slabp);
	}
}