[PATCH v3 34/49] ext4: dynamically allocate the ext4-es shrinker

[Qi Zheng]

On 2023/7/27 16:04, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the ext4-es 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 ext4_sb_info.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
> Reviewed-by: Muchun Song <songmuchun at bytedance.com>
> ---
>   fs/ext4/ext4.h           |  2 +-
>   fs/ext4/extents_status.c | 22 ++++++++++++----------
>   2 files changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1e2259d9967d..82397bf0b33e 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1657,7 +1657,7 @@ struct ext4_sb_info {
>   	__u32 s_csum_seed;
>   
>   	/* Reclaim extents from extent status tree */
> -	struct shrinker s_es_shrinker;
> +	struct shrinker *s_es_shrinker;
>   	struct list_head s_es_list;	/* List of inodes with reclaimable extents */
>   	long s_es_nr_inode;
>   	struct ext4_es_stats s_es_stats;
> diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
> index 9b5b8951afb4..74bb64fadbc4 100644
> --- a/fs/ext4/extents_status.c
> +++ b/fs/ext4/extents_status.c
> @@ -1596,7 +1596,7 @@ static unsigned long ext4_es_count(struct shrinker *shrink,
>   	unsigned long nr;
>   	struct ext4_sb_info *sbi;
>   
> -	sbi = container_of(shrink, struct ext4_sb_info, s_es_shrinker);
> +	sbi = shrink->private_data;
>   	nr = percpu_counter_read_positive(&sbi->s_es_stats.es_stats_shk_cnt);
>   	trace_ext4_es_shrink_count(sbi->s_sb, sc->nr_to_scan, nr);
>   	return nr;
> @@ -1605,8 +1605,7 @@ static unsigned long ext4_es_count(struct shrinker *shrink,
>   static unsigned long ext4_es_scan(struct shrinker *shrink,
>   				  struct shrink_control *sc)
>   {
> -	struct ext4_sb_info *sbi = container_of(shrink,
> -					struct ext4_sb_info, s_es_shrinker);
> +	struct ext4_sb_info *sbi = shrink->private_data;
>   	int nr_to_scan = sc->nr_to_scan;
>   	int ret, nr_shrunk;
>   
> @@ -1690,14 +1689,17 @@ int ext4_es_register_shrinker(struct ext4_sb_info *sbi)
>   	if (err)
>   		goto err3;
>   
> -	sbi->s_es_shrinker.scan_objects = ext4_es_scan;
> -	sbi->s_es_shrinker.count_objects = ext4_es_count;
> -	sbi->s_es_shrinker.seeks = DEFAULT_SEEKS;
> -	err = register_shrinker(&sbi->s_es_shrinker, "ext4-es:%s",
> -				sbi->s_sb->s_id);
> -	if (err)
> +	sbi->s_es_shrinker = shrinker_alloc(0, "ext4-es:%s", sbi->s_sb->s_id);
> +	if (!sbi->s_es_shrinker)

Here should set err to -ENOMEM, will fix.

>   		goto err4;
>   
> +	sbi->s_es_shrinker->scan_objects = ext4_es_scan;
> +	sbi->s_es_shrinker->count_objects = ext4_es_count;
> +	sbi->s_es_shrinker->seeks = DEFAULT_SEEKS;
> +	sbi->s_es_shrinker->private_data = sbi;
> +
> +	shrinker_register(sbi->s_es_shrinker);
> +
>   	return 0;
>   err4:
>   	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
> @@ -1716,7 +1718,7 @@ void ext4_es_unregister_shrinker(struct ext4_sb_info *sbi)
>   	percpu_counter_destroy(&sbi->s_es_stats.es_stats_cache_misses);
>   	percpu_counter_destroy(&sbi->s_es_stats.es_stats_all_cnt);
>   	percpu_counter_destroy(&sbi->s_es_stats.es_stats_shk_cnt);
> -	unregister_shrinker(&sbi->s_es_shrinker);
> +	shrinker_free(sbi->s_es_shrinker);
>   }
>   
>   /*