Re: [PATCH v3 27/49] dm: dynamically allocate the dm-bufio shrinker

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

On 2023/7/27 16:04, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the dm-bufio 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 dm_bufio_client.
>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>   drivers/md/dm-bufio.c | 26 +++++++++++++++-----------
>   1 file changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
> index bc309e41d074..5a9124b83d53 100644
> --- a/drivers/md/dm-bufio.c
> +++ b/drivers/md/dm-bufio.c
> @@ -963,7 +963,7 @@ struct dm_bufio_client {
>   
>   	sector_t start;
>   
> -	struct shrinker shrinker;
> +	struct shrinker *shrinker;
>   	struct work_struct shrink_work;
>   	atomic_long_t need_shrink;
>   
> @@ -2368,7 +2368,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
>   {
>   	struct dm_bufio_client *c;
>   
> -	c = container_of(shrink, struct dm_bufio_client, shrinker);
> +	c = shrink->private_data;
>   	atomic_long_add(sc->nr_to_scan, &c->need_shrink);
>   	queue_work(dm_bufio_wq, &c->shrink_work);
>   
> @@ -2377,7 +2377,7 @@ static unsigned long dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink
>   
>   static unsigned long dm_bufio_shrink_count(struct shrinker *shrink, struct shrink_control *sc)
>   {
> -	struct dm_bufio_client *c = container_of(shrink, struct dm_bufio_client, shrinker);
> +	struct dm_bufio_client *c = shrink->private_data;
>   	unsigned long count = cache_total(&c->cache);
>   	unsigned long retain_target = get_retain_buffers(c);
>   	unsigned long queued_for_cleanup = atomic_long_read(&c->need_shrink);
> @@ -2490,15 +2490,19 @@ struct dm_bufio_client *dm_bufio_client_create(struct block_device *bdev, unsign
>   	INIT_WORK(&c->shrink_work, shrink_work);
>   	atomic_long_set(&c->need_shrink, 0);
>   
> -	c->shrinker.count_objects = dm_bufio_shrink_count;
> -	c->shrinker.scan_objects = dm_bufio_shrink_scan;
> -	c->shrinker.seeks = 1;
> -	c->shrinker.batch = 0;
> -	r = register_shrinker(&c->shrinker, "dm-bufio:(%u:%u)",
> -			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
> -	if (r)
> +	c->shrinker = shrinker_alloc(0, "dm-bufio:(%u:%u)",
> +				     MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
> +	if (!c->shrinker)

Here should set r to -ENOMEM, will fix.

>   		goto bad;
>   
> +	c->shrinker->count_objects = dm_bufio_shrink_count;
> +	c->shrinker->scan_objects = dm_bufio_shrink_scan;
> +	c->shrinker->seeks = 1;
> +	c->shrinker->batch = 0;
> +	c->shrinker->private_data = c;
> +
> +	shrinker_register(c->shrinker);
> +
>   	mutex_lock(&dm_bufio_clients_lock);
>   	dm_bufio_client_count++;
>   	list_add(&c->client_list, &dm_bufio_all_clients);
> @@ -2537,7 +2541,7 @@ void dm_bufio_client_destroy(struct dm_bufio_client *c)
>   
>   	drop_buffers(c);
>   
> -	unregister_shrinker(&c->shrinker);
> +	shrinker_free(c->shrinker);
>   	flush_work(&c->shrink_work);
>   
>   	mutex_lock(&dm_bufio_clients_lock);