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

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Message-ID: <961f6055-a395-8490-4c22-765a30668460@bytedance.com>
Date:   Thu, 27 Jul 2023 17:13:07 +0800
From:   Qi Zheng <zhengqi.arch@...edance.com>
To:     akpm@...ux-foundation.org, david@...morbit.com, tkhai@...ru,
        vbabka@...e.cz, roman.gushchin@...ux.dev, djwong@...nel.org,
        brauner@...nel.org, paulmck@...nel.org, tytso@....edu,
        steven.price@....com, cel@...nel.org, senozhatsky@...omium.org,
        yujie.liu@...el.com, gregkh@...uxfoundation.org,
        muchun.song@...ux.dev
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        kvm@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-erofs@...ts.ozlabs.org,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-nfs@...r.kernel.org, linux-mtd@...ts.infradead.org,
        rcu@...r.kernel.org, netdev@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        dm-devel@...hat.com, linux-raid@...r.kernel.org,
        linux-bcache@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>
Subject: Re: [PATCH v3 27/49] dm: dynamically allocate the dm-bufio shrinker



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@...edance.com>
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> ---
>   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);