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

[Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>]

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@xxxxxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
CC: "Theodore Ts'o" <tytso@xxxxxxx>
CC: Jan Kara <jack@xxxxxxxx>
CC: linux-ext4@xxxxxxxxxxxxxxx
---
 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