linux-kernel - Re: [PATCH v3 28/49] dm zoned: dynamically allocate the dm-zoned-meta shrinker

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Message-ID: <baaf7de4-9a0e-b953-2b6a-46e60c415614@kernel.org>
Date:   Thu, 27 Jul 2023 17:30:01 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     Qi Zheng <zhengqi.arch@...edance.com>, 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 28/49] dm zoned: dynamically allocate the dm-zoned-meta
 shrinker

On 7/27/23 17:04, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the dm-zoned-meta 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 dmz_metadata.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> ---
>  drivers/md/dm-zoned-metadata.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
> index 9d3cca8e3dc9..0bcb26a43578 100644
> --- a/drivers/md/dm-zoned-metadata.c
> +++ b/drivers/md/dm-zoned-metadata.c
> @@ -187,7 +187,7 @@ struct dmz_metadata {
>  	struct rb_root		mblk_rbtree;
>  	struct list_head	mblk_lru_list;
>  	struct list_head	mblk_dirty_list;
> -	struct shrinker		mblk_shrinker;
> +	struct shrinker		*mblk_shrinker;
>  
>  	/* Zone allocation management */
>  	struct mutex		map_lock;
> @@ -615,7 +615,7 @@ static unsigned long dmz_shrink_mblock_cache(struct dmz_metadata *zmd,
>  static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
>  					       struct shrink_control *sc)
>  {
> -	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
> +	struct dmz_metadata *zmd = shrink->private_data;
>  
>  	return atomic_read(&zmd->nr_mblks);
>  }
> @@ -626,7 +626,7 @@ static unsigned long dmz_mblock_shrinker_count(struct shrinker *shrink,
>  static unsigned long dmz_mblock_shrinker_scan(struct shrinker *shrink,
>  					      struct shrink_control *sc)
>  {
> -	struct dmz_metadata *zmd = container_of(shrink, struct dmz_metadata, mblk_shrinker);
> +	struct dmz_metadata *zmd = shrink->private_data;
>  	unsigned long count;
>  
>  	spin_lock(&zmd->mblk_lock);
> @@ -2936,19 +2936,23 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
>  	 */
>  	zmd->min_nr_mblks = 2 + zmd->nr_map_blocks + zmd->zone_nr_bitmap_blocks * 16;
>  	zmd->max_nr_mblks = zmd->min_nr_mblks + 512;
> -	zmd->mblk_shrinker.count_objects = dmz_mblock_shrinker_count;
> -	zmd->mblk_shrinker.scan_objects = dmz_mblock_shrinker_scan;
> -	zmd->mblk_shrinker.seeks = DEFAULT_SEEKS;
>  
>  	/* Metadata cache shrinker */
> -	ret = register_shrinker(&zmd->mblk_shrinker, "dm-zoned-meta:(%u:%u)",
> -				MAJOR(dev->bdev->bd_dev),
> -				MINOR(dev->bdev->bd_dev));
> -	if (ret) {
> -		dmz_zmd_err(zmd, "Register metadata cache shrinker failed");
> +	zmd->mblk_shrinker = shrinker_alloc(0,  "dm-zoned-meta:(%u:%u)",
> +					    MAJOR(dev->bdev->bd_dev),
> +					    MINOR(dev->bdev->bd_dev));
> +	if (!zmd->mblk_shrinker) {
> +		dmz_zmd_err(zmd, "Allocate metadata cache shrinker failed");

ret is not set here, so dmz_ctr_metadata() will return success. You need to add:
		ret = -ENOMEM;
or something.
>  		goto err;
>  	}
>  
> +	zmd->mblk_shrinker->count_objects = dmz_mblock_shrinker_count;
> +	zmd->mblk_shrinker->scan_objects = dmz_mblock_shrinker_scan;
> +	zmd->mblk_shrinker->seeks = DEFAULT_SEEKS;
> +	zmd->mblk_shrinker->private_data = zmd;
> +
> +	shrinker_register(zmd->mblk_shrinker);

I fail to see how this new shrinker API is better... Why isn't there a
shrinker_alloc_and_register() function ? That would avoid adding all this code
all over the place as the new API call would be very similar to the current
shrinker_register() call with static allocation.

> +
>  	dmz_zmd_info(zmd, "DM-Zoned metadata version %d", zmd->sb_version);
>  	for (i = 0; i < zmd->nr_devs; i++)
>  		dmz_print_dev(zmd, i);
> @@ -2995,7 +2999,7 @@ int dmz_ctr_metadata(struct dmz_dev *dev, int num_dev,
>   */
>  void dmz_dtr_metadata(struct dmz_metadata *zmd)
>  {
> -	unregister_shrinker(&zmd->mblk_shrinker);
> +	shrinker_free(zmd->mblk_shrinker);
>  	dmz_cleanup_metadata(zmd);
>  	kfree(zmd);
>  }

-- 
Damien Le Moal
Western Digital Research