[PATCH v4 34/48] 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 using kfree_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>
---
 fs/jbd2/journal.c    | 27 +++++++++++++++++----------
 include/linux/jbd2.h |  2 +-
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 1b5a45ab62b0..4c421da03fee 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1298,7 +1298,7 @@ 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;
@@ -1324,7 +1324,7 @@ 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);
@@ -1412,19 +1412,26 @@ static journal_t *journal_init_common(struct block_device *bdev,
 	journal->j_superblock = (journal_superblock_t *)bh->b_data;
 
 	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;
 
 	if (percpu_counter_init(&journal->j_checkpoint_jh_count, 0, GFP_KERNEL))
 		goto err_cleanup;
 
-	if (register_shrinker(&journal->j_shrinker, "jbd2-journal:(%u:%u)",
-			      MAJOR(bdev->bd_dev), MINOR(bdev->bd_dev))) {
+	journal->j_shrinker = shrinker_alloc(0, "jbd2-journal:(%u:%u)",
+					     MAJOR(bdev->bd_dev),
+					     MINOR(bdev->bd_dev));
+	if (!journal->j_shrinker) {
 		percpu_counter_destroy(&journal->j_checkpoint_jh_count);
 		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;
 
 err_cleanup:
@@ -2187,9 +2194,9 @@ 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 44c298aa58d4..beb4c4586320 100644
--- a/include/linux/jbd2.h
+++ b/include/linux/jbd2.h
@@ -891,7 +891,7 @@ 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