Re: [PATCH v3 29/49] md/raid5: dynamically allocate the md-raid5 shrinker

[Qi Zheng <zhengqi.arch@bytedance.com>]

On 2023/7/27 16:04, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the md-raid5 shrinker, so that it can be freed
> asynchronously using kfree_rcu(). Then it doesn't need to wait for RCU
> read-side critical section when releasing the struct r5conf.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@bytedance.com>
> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
> ---
>   drivers/md/raid5.c | 25 ++++++++++++++-----------
>   drivers/md/raid5.h |  2 +-
>   2 files changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 85b3004594e0..fbb4e6f5ff43 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -7414,7 +7414,7 @@ static void free_conf(struct r5conf *conf)
>   
>   	log_exit(conf);
>   
> -	unregister_shrinker(&conf->shrinker);
> +	shrinker_free(conf->shrinker);
>   	free_thread_groups(conf);
>   	shrink_stripes(conf);
>   	raid5_free_percpu(conf);
> @@ -7462,7 +7462,7 @@ static int raid5_alloc_percpu(struct r5conf *conf)
>   static unsigned long raid5_cache_scan(struct shrinker *shrink,
>   				      struct shrink_control *sc)
>   {
> -	struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);
> +	struct r5conf *conf = shrink->private_data;
>   	unsigned long ret = SHRINK_STOP;
>   
>   	if (mutex_trylock(&conf->cache_size_mutex)) {
> @@ -7483,7 +7483,7 @@ static unsigned long raid5_cache_scan(struct shrinker *shrink,
>   static unsigned long raid5_cache_count(struct shrinker *shrink,
>   				       struct shrink_control *sc)
>   {
> -	struct r5conf *conf = container_of(shrink, struct r5conf, shrinker);
> +	struct r5conf *conf = shrink->private_data;
>   
>   	if (conf->max_nr_stripes < conf->min_nr_stripes)
>   		/* unlikely, but not impossible */
> @@ -7718,18 +7718,21 @@ static struct r5conf *setup_conf(struct mddev *mddev)
>   	 * it reduces the queue depth and so can hurt throughput.
>   	 * So set it rather large, scaled by number of devices.
>   	 */
> -	conf->shrinker.seeks = DEFAULT_SEEKS * conf->raid_disks * 4;
> -	conf->shrinker.scan_objects = raid5_cache_scan;
> -	conf->shrinker.count_objects = raid5_cache_count;
> -	conf->shrinker.batch = 128;
> -	conf->shrinker.flags = 0;
> -	ret = register_shrinker(&conf->shrinker, "md-raid5:%s", mdname(mddev));
> -	if (ret) {
> -		pr_warn("md/raid:%s: couldn't register shrinker.\n",
> +	conf->shrinker = shrinker_alloc(0, "md-raid5:%s", mdname(mddev));
> +	if (!conf->shrinker) {

Here should set ret to -ENOMEM, will fix.

> +		pr_warn("md/raid:%s: couldn't allocate shrinker.\n",
>   			mdname(mddev));
>   		goto abort;
>   	}
>   
> +	conf->shrinker->seeks = DEFAULT_SEEKS * conf->raid_disks * 4;
> +	conf->shrinker->scan_objects = raid5_cache_scan;
> +	conf->shrinker->count_objects = raid5_cache_count;
> +	conf->shrinker->batch = 128;
> +	conf->shrinker->private_data = conf;
> +
> +	shrinker_register(conf->shrinker);
> +
>   	sprintf(pers_name, "raid%d", mddev->new_level);
>   	rcu_assign_pointer(conf->thread,
>   			   md_register_thread(raid5d, mddev, pers_name));
> diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
> index 97a795979a35..22bea20eccbd 100644
> --- a/drivers/md/raid5.h
> +++ b/drivers/md/raid5.h
> @@ -670,7 +670,7 @@ struct r5conf {
>   	wait_queue_head_t	wait_for_stripe;
>   	wait_queue_head_t	wait_for_overlap;
>   	unsigned long		cache_state;
> -	struct shrinker		shrinker;
> +	struct shrinker		*shrinker;
>   	int			pool_size; /* number of disks in stripeheads in pool */
>   	spinlock_t		device_lock;
>   	struct disk_info	*disks;