linux-kernel - Re: [PATCH v5 31/45] jbd2,ext4: dynamically allocate the jbd2-journal shrinker

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Message-ID: <20230824094954.ndobdyabdxw3xvbc@quack3>
Date:   Thu, 24 Aug 2023 11:49:54 +0200
From:   Jan Kara <jack@...e.cz>
To:     Qi Zheng <zhengqi.arch@...edance.com>
Cc:     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, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Jan Kara <jack@...e.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v5 31/45] jbd2,ext4: dynamically allocate the
 jbd2-journal shrinker

On Thu 24-08-23 11:42:50, Qi Zheng wrote:
> In preparation for implementing lockless slab shrink, use new APIs to
> dynamically allocate the jbd2-journal shrinker, so that it can be freed
> asynchronously via RCU. Then it doesn't need to wait for RCU read-side
> critical section when releasing the struct journal_s.
> 
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> Reviewed-by: Muchun Song <songmuchun@...edance.com>
> CC: "Theodore Ts'o" <tytso@....edu>
> CC: Jan Kara <jack@...e.com>
> CC: linux-ext4@...r.kernel.org

Looks good to me. Feel free to add:

Acked-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/jbd2/journal.c    | 30 +++++++++++++++++++-----------
>  include/linux/jbd2.h |  2 +-
>  2 files changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
> index 768fa05bcbed..75692baa76e8 100644
> --- a/fs/jbd2/journal.c
> +++ b/fs/jbd2/journal.c
> @@ -1290,7 +1290,7 @@ static int jbd2_min_tag_size(void)
>  static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
>  					      struct shrink_control *sc)
>  {
> -	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
> +	journal_t *journal = shrink->private_data;
>  	unsigned long nr_to_scan = sc->nr_to_scan;
>  	unsigned long nr_shrunk;
>  	unsigned long count;
> @@ -1316,7 +1316,7 @@ static unsigned long jbd2_journal_shrink_scan(struct shrinker *shrink,
>  static unsigned long jbd2_journal_shrink_count(struct shrinker *shrink,
>  					       struct shrink_control *sc)
>  {
> -	journal_t *journal = container_of(shrink, journal_t, j_shrinker);
> +	journal_t *journal = shrink->private_data;
>  	unsigned long count;
>  
>  	count = percpu_counter_read_positive(&journal->j_checkpoint_jh_count);
> @@ -1588,14 +1588,22 @@ static journal_t *journal_init_common(struct block_device *bdev,
>  		goto err_cleanup;
>  
>  	journal->j_shrink_transaction = NULL;
> -	journal->j_shrinker.scan_objects = jbd2_journal_shrink_scan;
> -	journal->j_shrinker.count_objects = jbd2_journal_shrink_count;
> -	journal->j_shrinker.seeks = DEFAULT_SEEKS;
> -	journal->j_shrinker.batch = journal->j_max_transaction_buffers;
> -	err = register_shrinker(&journal->j_shrinker, "jbd2-journal:(%u:%u)",
> -				MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev));
> -	if (err)
> +
> +	journal->j_shrinker = shrinker_alloc(0, "jbd2-journal:(%u:%u)",
> +					     MAJOR(bdev->bd_dev),
> +					     MINOR(bdev->bd_dev));
> +	if (!journal->j_shrinker) {
> +		err = -ENOMEM;
>  		goto err_cleanup;
> +	}
> +
> +	journal->j_shrinker->scan_objects = jbd2_journal_shrink_scan;
> +	journal->j_shrinker->count_objects = jbd2_journal_shrink_count;
> +	journal->j_shrinker->seeks = DEFAULT_SEEKS;
> +	journal->j_shrinker->batch = journal->j_max_transaction_buffers;
> +	journal->j_shrinker->private_data = journal;
> +
> +	shrinker_register(journal->j_shrinker);
>  
>  	return journal;
>  
> @@ -2170,9 +2178,9 @@ int jbd2_journal_destroy(journal_t *journal)
>  		brelse(journal->j_sb_buffer);
>  	}
>  
> -	if (journal->j_shrinker.flags & SHRINKER_REGISTERED) {
> +	if (journal->j_shrinker) {
>  		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
> -		unregister_shrinker(&journal->j_shrinker);
> +		shrinker_free(journal->j_shrinker);
>  	}
>  	if (journal->j_proc_entry)
>  		jbd2_stats_proc_exit(journal);
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 52772c826c86..6dcbb4eb80fb 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -886,7 +886,7 @@ struct journal_s
>  	 * Journal head shrinker, reclaim buffer's journal head which
>  	 * has been written back.
>  	 */
> -	struct shrinker		j_shrinker;
> +	struct shrinker		*j_shrinker;
>  
>  	/**
>  	 * @j_checkpoint_jh_count:
> -- 
> 2.30.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR