bcachefs: Move gc of bucket.oldest_gen to workqueue

This is a nice cleanup - and we've also been having problems with
kthread creation in the mount path.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/alloc_background.c

@@ -874,7 +874,7 @@ int bch2_trigger_alloc(struct btree_trans *trans,
 			bch2_do_invalidates(c);
 
 		if (statechange(a->data_type == BCH_DATA_need_gc_gens))
-			bch2_do_gc_gens(c);
+			bch2_gc_gens_async(c);
 	}
 
 	if ((flags & BTREE_TRIGGER_gc) &&

fs/bcachefs/alloc_foreground.c

@@ -541,7 +541,7 @@ static struct open_bucket *bch2_bucket_alloc_trans(struct btree_trans *trans,
 		bch2_do_discards(c);
 
 	if (usage->d[BCH_DATA_need_gc_gens].buckets > avail)
-		bch2_do_gc_gens(c);
+		bch2_gc_gens_async(c);
 
 	if (should_invalidate_buckets(ca, *usage))
 		bch2_do_invalidates(c);

fs/bcachefs/bcachefs.h

@@ -718,6 +718,7 @@ struct btree_trans_buf {
 	x(discard_fast)							\
 	x(invalidate)							\
 	x(delete_dead_snapshots)					\
+	x(gc_gens)							\
 	x(snapshot_delete_pagecache)					\
 	x(sysfs)							\
 	x(btree_write_buffer)
@@ -960,8 +961,7 @@ struct bch_fs {
 	struct work_struct	discard_fast_work;
 
 	/* GARBAGE COLLECTION */
-	struct task_struct	*gc_thread;
-	atomic_t		kick_gc;
+	struct work_struct	gc_gens_work;
 	unsigned long		gc_count;
 
 	enum btree_id		gc_gens_btree;
@@ -1118,7 +1118,6 @@ struct bch_fs {
 	u64			counters_on_mount[BCH_COUNTER_NR];
 	u64 __percpu		*counters;
 
-	unsigned		btree_gc_periodic:1;
 	unsigned		copy_gc_enabled:1;
 	bool			promote_whole_extents;
 

fs/bcachefs/btree_gc.c

@@ -1669,6 +1669,9 @@ static int gc_btree_gens_key(struct btree_trans *trans,
 	struct bkey_i *u;
 	int ret;
 
+	if (unlikely(test_bit(BCH_FS_going_ro, &c->flags)))
+		return -EROFS;
+
 	percpu_down_read(&c->mark_lock);
 	bkey_for_each_ptr(ptrs, ptr) {
 		struct bch_dev *ca = bch2_dev_bkey_exists(c, ptr->dev);
@@ -1802,80 +1805,23 @@ int bch2_gc_gens(struct bch_fs *c)
 	return ret;
 }
 
-static int bch2_gc_thread(void *arg)
+static void bch2_gc_gens_work(struct work_struct *work)
 {
-	struct bch_fs *c = arg;
-	struct io_clock *clock = &c->io_clock[WRITE];
-	unsigned long last = atomic64_read(&clock->now);
-	unsigned last_kick = atomic_read(&c->kick_gc);
-
-	set_freezable();
-
-	while (1) {
-		while (1) {
-			set_current_state(TASK_INTERRUPTIBLE);
-
-			if (kthread_should_stop()) {
-				__set_current_state(TASK_RUNNING);
-				return 0;
-			}
-
-			if (atomic_read(&c->kick_gc) != last_kick)
-				break;
-
-			if (c->btree_gc_periodic) {
-				unsigned long next = last + c->capacity / 16;
-
-				if (atomic64_read(&clock->now) >= next)
-					break;
-
-				bch2_io_clock_schedule_timeout(clock, next);
-			} else {
-				schedule();
-			}
-
-			try_to_freeze();
-		}
-		__set_current_state(TASK_RUNNING);
-
-		last = atomic64_read(&clock->now);
-		last_kick = atomic_read(&c->kick_gc);
-
-		bch2_gc_gens(c);
-		debug_check_no_locks_held();
-	}
-
-	return 0;
+	struct bch_fs *c = container_of(work, struct bch_fs, gc_gens_work);
+	bch2_gc_gens(c);
+	bch2_write_ref_put(c, BCH_WRITE_REF_gc_gens);
 }
 
-void bch2_gc_thread_stop(struct bch_fs *c)
+void bch2_gc_gens_async(struct bch_fs *c)
 {
-	struct task_struct *p;
-
-	p = c->gc_thread;
-	c->gc_thread = NULL;
-
-	if (p) {
-		kthread_stop(p);
-		put_task_struct(p);
-	}
+	if (bch2_write_ref_tryget(c, BCH_WRITE_REF_gc_gens) &&
+	    !queue_work(c->write_ref_wq, &c->gc_gens_work))
+		bch2_write_ref_put(c, BCH_WRITE_REF_gc_gens);
 }
 
-int bch2_gc_thread_start(struct bch_fs *c)
+void bch2_fs_gc_init(struct bch_fs *c)
 {
-	struct task_struct *p;
-
-	if (c->gc_thread)
-		return 0;
+	seqcount_init(&c->gc_pos_lock);
 
-	p = kthread_create(bch2_gc_thread, c, "bch-gc/%s", c->name);
-	if (IS_ERR(p)) {
-		bch_err_fn(c, PTR_ERR(p));
-		return PTR_ERR(p);
-	}
-
-	get_task_struct(p);
-	c->gc_thread = p;
-	wake_up_process(p);
-	return 0;
+	INIT_WORK(&c->gc_gens_work, bch2_gc_gens_work);
 }

fs/bcachefs/btree_gc.h

@@ -7,9 +7,6 @@
 
 int bch2_check_topology(struct bch_fs *);
 int bch2_check_allocations(struct bch_fs *);
-int bch2_gc_gens(struct bch_fs *);
-void bch2_gc_thread_stop(struct bch_fs *);
-int bch2_gc_thread_start(struct bch_fs *);
 
 /*
  * For concurrent mark and sweep (with other index updates), we define a total
@@ -104,11 +101,8 @@ static inline bool gc_visited(struct bch_fs *c, struct gc_pos pos)
 	return ret;
 }
 
-static inline void bch2_do_gc_gens(struct bch_fs *c)
-{
-	atomic_inc(&c->kick_gc);
-	if (c->gc_thread)
-		wake_up_process(c->gc_thread);
-}
+int bch2_gc_gens(struct bch_fs *);
+void bch2_gc_gens_async(struct bch_fs *);
+void bch2_fs_gc_init(struct bch_fs *);
 
 #endif /* _BCACHEFS_BTREE_GC_H */

fs/bcachefs/super.c

@@ -264,7 +264,6 @@ static void __bch2_fs_read_only(struct bch_fs *c)
 	bch2_open_buckets_stop(c, NULL, true);
 	bch2_rebalance_stop(c);
 	bch2_copygc_stop(c);
-	bch2_gc_thread_stop(c);
 	bch2_fs_ec_flush(c);
 
 	bch_verbose(c, "flushing journal and stopping allocators, journal seq %llu",
@@ -486,12 +485,6 @@ static int __bch2_fs_read_write(struct bch_fs *c, bool early)
 	}
 #endif
 
-	ret = bch2_gc_thread_start(c);
-	if (ret) {
-		bch_err(c, "error starting gc thread");
-		return ret;
-	}
-
 	ret = bch2_journal_reclaim_start(&c->journal);
 	if (ret)
 		goto err;
@@ -780,6 +773,7 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 	for (i = 0; i < BCH_TIME_STAT_NR; i++)
 		bch2_time_stats_init(&c->times[i]);
 
+	bch2_fs_gc_init(c);
 	bch2_fs_copygc_init(c);
 	bch2_fs_btree_key_cache_init_early(&c->btree_key_cache);
 	bch2_fs_btree_iter_init_early(c);
@@ -810,8 +804,6 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 	INIT_LIST_HEAD(&c->fsck_error_msgs);
 	mutex_init(&c->fsck_error_msgs_lock);
 
-	seqcount_init(&c->gc_pos_lock);
-
 	seqcount_init(&c->usage_lock);
 
 	sema_init(&c->io_in_flight, 128);

fs/bcachefs/sysfs.c

@@ -142,7 +142,6 @@ write_attribute(trigger_invalidates);
 write_attribute(trigger_journal_flush);
 write_attribute(prune_cache);
 write_attribute(btree_wakeup);
-rw_attribute(btree_gc_periodic);
 rw_attribute(gc_gens_pos);
 
 read_attribute(uuid);
@@ -408,8 +407,6 @@ SHOW(bch2_fs)
 	if (attr == &sysfs_btree_write_stats)
 		bch2_btree_write_stats_to_text(out, c);
 
-	sysfs_printf(btree_gc_periodic, "%u",	(int) c->btree_gc_periodic);
-
 	if (attr == &sysfs_gc_gens_pos)
 		bch2_gc_gens_pos_to_text(out, c);
 
@@ -485,14 +482,6 @@ STORE(bch2_fs)
 {
 	struct bch_fs *c = container_of(kobj, struct bch_fs, kobj);
 
-	if (attr == &sysfs_btree_gc_periodic) {
-		ssize_t ret = strtoul_safe(buf, c->btree_gc_periodic)
-			?: (ssize_t) size;
-
-		wake_up_process(c->gc_thread);
-		return ret;
-	}
-
 	if (attr == &sysfs_copy_gc_enabled) {
 		ssize_t ret = strtoul_safe(buf, c->copy_gc_enabled)
 			?: (ssize_t) size;