bcachefs: Knob for manual snapshot deletion

Add 'opts.snapshot_deletion_enabled', enabled by default.

This may be turned off so that the new sysfs knob,
'internal/trigger_delete_dead_snapshots', may be used instead - this
will allow snapshot deletion to be profiled more easily.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/opts.h

@@ -495,6 +495,12 @@ enum fsck_err_opts {
 	  OPT_BOOL(),							\
 	  BCH_SB_REBALANCE_AC_ONLY,		false,			\
 	  NULL,		"Enable rebalance while on mains power only\n")	\
+	x(auto_snapshot_deletion,	u8,				\
+	  OPT_FS|OPT_MOUNT|OPT_RUNTIME,					\
+	  OPT_BOOL(),							\
+	  BCH2_NO_SB_OPT,			true,			\
+	  NULL,		"Enable automatic snapshot deletion: disable for debugging, or to\n"\
+			"quiet the system when doing performance testing\n")\
 	x(no_data_io,			u8,				\
 	  OPT_MOUNT,							\
 	  OPT_BOOL(),							\

fs/bcachefs/snapshot.c

@@ -1776,15 +1776,19 @@ static void bch2_snapshot_delete_nodes_to_text(struct printbuf *out, struct snap
 	prt_newline(out);
 }
 
-int bch2_delete_dead_snapshots(struct bch_fs *c)
+int __bch2_delete_dead_snapshots(struct bch_fs *c)
 {
-	if (!test_and_clear_bit(BCH_FS_need_delete_dead_snapshots, &c->flags))
-		return 0;
-
-	struct btree_trans *trans = bch2_trans_get(c);
 	struct snapshot_delete *d = &c->snapshot_delete;
 	int ret = 0;
 
+	if (!mutex_trylock(&d->lock))
+		return 0;
+
+	if (!test_and_clear_bit(BCH_FS_need_delete_dead_snapshots, &c->flags))
+		goto out_unlock;
+
+	struct btree_trans *trans = bch2_trans_get(c);
+
 	/*
 	 * For every snapshot node: If we have no live children and it's not
 	 * pointed to by a subvolume, delete it:
@@ -1857,11 +1861,21 @@ err:
 	d->running = false;
 	mutex_unlock(&d->progress_lock);
 	bch2_trans_put(trans);
+out_unlock:
+	mutex_unlock(&d->lock);
 	if (!bch2_err_matches(ret, EROFS))
 		bch_err_fn(c, ret);
 	return ret;
 }
 
+int bch2_delete_dead_snapshots(struct bch_fs *c)
+{
+	if (!c->opts.auto_snapshot_deletion)
+		return 0;
+
+	return __bch2_delete_dead_snapshots(c);
+}
+
 void bch2_delete_dead_snapshots_work(struct work_struct *work)
 {
 	struct bch_fs *c = container_of(work, struct bch_fs, snapshot_delete.work);
@@ -1874,6 +1888,9 @@ void bch2_delete_dead_snapshots_work(struct work_struct *work)
 
 void bch2_delete_dead_snapshots_async(struct bch_fs *c)
 {
+	if (!c->opts.auto_snapshot_deletion)
+		return;
+
 	if (!enumerated_ref_tryget(&c->writes, BCH_WRITE_REF_delete_dead_snapshots))
 		return;
 
@@ -1977,6 +1994,7 @@ void bch2_fs_snapshots_exit(struct bch_fs *c)
 void bch2_fs_snapshots_init_early(struct bch_fs *c)
 {
 	INIT_WORK(&c->snapshot_delete.work, bch2_delete_dead_snapshots_work);
+	mutex_init(&c->snapshot_delete.lock);
 	mutex_init(&c->snapshot_delete.progress_lock);
 	mutex_init(&c->snapshots_unlinked_lock);
 }

fs/bcachefs/snapshot.h

@@ -273,6 +273,7 @@ static inline int bch2_key_has_snapshot_overwrites(struct btree_trans *trans,
 	return __bch2_key_has_snapshot_overwrites(trans, id, pos);
 }
 
+int __bch2_delete_dead_snapshots(struct bch_fs *);
 int bch2_delete_dead_snapshots(struct bch_fs *);
 void bch2_delete_dead_snapshots_work(struct work_struct *);
 void bch2_delete_dead_snapshots_async(struct bch_fs *);

fs/bcachefs/snapshot_types.h

@@ -42,6 +42,7 @@ struct snapshot_interior_delete {
 typedef DARRAY(struct snapshot_interior_delete) interior_delete_list;
 
 struct snapshot_delete {
+	struct mutex		lock;
 	struct work_struct	work;
 
 	struct mutex		progress_lock;

fs/bcachefs/sysfs.c

@@ -149,6 +149,7 @@ write_attribute(trigger_btree_key_cache_shrink);
 write_attribute(trigger_btree_updates);
 write_attribute(trigger_freelist_wakeup);
 write_attribute(trigger_recalc_capacity);
+write_attribute(trigger_delete_dead_snapshots);
 read_attribute(gc_gens_pos);
 
 read_attribute(uuid);
@@ -439,6 +440,9 @@ STORE(bch2_fs)
 		up_read(&c->state_lock);
 	}
 
+	if (attr == &sysfs_trigger_delete_dead_snapshots)
+		__bch2_delete_dead_snapshots(c);
+
 #ifdef CONFIG_BCACHEFS_TESTS
 	if (attr == &sysfs_perf_test) {
 		char *tmp = kstrdup(buf, GFP_KERNEL), *p = tmp;
@@ -568,6 +572,7 @@ struct attribute *bch2_fs_internal_files[] = {
 	&sysfs_trigger_btree_updates,
 	&sysfs_trigger_freelist_wakeup,
 	&sysfs_trigger_recalc_capacity,
+	&sysfs_trigger_delete_dead_snapshots,
 
 	&sysfs_gc_gens_pos,