how to free slab object?

When an allocated object is no longer required, it must be returned to the slab allocator using kmem_cache_free.
 

/**
 * kmem_cache_free - Deallocate an object
 * @cachep: The cache the allocation was from.
 * @objp: The previously allocated object.
 *
 * Free an object which was previously allocated from this
 * cache.
 */
void kmem_cache_free(struct kmem_cache *cachep, void *objp)
{
    unsigned long flags;

    local_irq_save(flags);
    debug_check_no_locks_freed(objp, obj_size(cachep));
    if (!(cachep->flags & SLAB_DEBUG_OBJECTS))
        debug_check_no_obj_freed(objp, obj_size(cachep));
    __cache_free(cachep, objp);
    local_irq_restore(flags);

    trace_kmem_cache_free(_RET_IP_, objp);
}
EXPORT_SYMBOL(kmem_cache_free);