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

[Damien Le Moal <dlemoal@xxxxxxxxxx>]

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@xxxxxxxxxxxxx>
> Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>  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