bcachefs: Bucket invalidate path improvements

 - invalidate_one_bucket() now returns 1 when we don't have any buckets
   on this device to invalidate, ensuring we don't spin
 - the tracepoint invocation is moved to after the transaction commit,
   and we now include the number of cached sectors in the tracepoint
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/alloc_background.c

@@ -1077,7 +1077,8 @@ void bch2_do_discards(struct bch_fs *c)
 		percpu_ref_put(&c->writes);
 }
 
-static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca)
+static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca,
+				 struct bpos *bucket_pos, unsigned *cached_sectors)
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter lru_iter, alloc_iter = { NULL };
@@ -1095,8 +1096,10 @@ static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca)
 	if (ret)
 		goto out;
 
-	if (!k.k || k.k->p.inode != ca->dev_idx)
+	if (!k.k || k.k->p.inode != ca->dev_idx) {
+		ret = 1;
 		goto out;
+	}
 
 	if (k.k->type != KEY_TYPE_lru) {
 		prt_printf(&buf, "non lru key in lru btree:\n  ");
@@ -1116,8 +1119,9 @@ static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca)
 	idx	= k.k->p.offset;
 	bucket	= le64_to_cpu(bkey_s_c_to_lru(k).v->idx);
 
-	a = bch2_trans_start_alloc_update(trans, &alloc_iter,
-					  POS(ca->dev_idx, bucket));
+	*bucket_pos = POS(ca->dev_idx, bucket);
+
+	a = bch2_trans_start_alloc_update(trans, &alloc_iter, *bucket_pos);
 	ret = PTR_ERR_OR_ZERO(a);
 	if (ret)
 		goto out;
@@ -1139,6 +1143,11 @@ static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca)
 		}
 	}
 
+	if (!a->v.cached_sectors)
+		bch_err(c, "invalidating empty bucket, confused");
+
+	*cached_sectors = a->v.cached_sectors;
+
 	SET_BCH_ALLOC_V4_NEED_INC_GEN(&a->v, false);
 	a->v.gen++;
 	a->v.data_type		= 0;
@@ -1151,8 +1160,6 @@ static int invalidate_one_bucket(struct btree_trans *trans, struct bch_dev *ca)
 				BTREE_TRIGGER_BUCKET_INVALIDATE);
 	if (ret)
 		goto out;
-
-	trace_invalidate_bucket(c, a->k.p.inode, a->k.p.offset);
 out:
 	bch2_trans_iter_exit(trans, &alloc_iter);
 	bch2_trans_iter_exit(trans, &lru_iter);
@@ -1165,7 +1172,8 @@ static void bch2_do_invalidates_work(struct work_struct *work)
 	struct bch_fs *c = container_of(work, struct bch_fs, invalidate_work);
 	struct bch_dev *ca;
 	struct btree_trans trans;
-	unsigned i;
+	struct bpos bucket;
+	unsigned i, sectors;
 	int ret = 0;
 
 	bch2_trans_init(&trans, c, 0, 0);
@@ -1178,10 +1186,12 @@ static void bch2_do_invalidates_work(struct work_struct *work)
 			ret = __bch2_trans_do(&trans, NULL, NULL,
 					      BTREE_INSERT_USE_RESERVE|
 					      BTREE_INSERT_NOFAIL,
-					invalidate_one_bucket(&trans, ca));
+					invalidate_one_bucket(&trans, ca, &bucket,
+							      &sectors));
 			if (ret)
 				break;
 
+			trace_invalidate_bucket(c, bucket.inode, bucket.offset, sectors);
 			this_cpu_inc(c->counters[BCH_COUNTER_bucket_invalidate]);
 		}
 	}

fs/bcachefs/trace.h

@@ -542,24 +542,27 @@ TRACE_EVENT(discard_buckets,
 );
 
 TRACE_EVENT(invalidate_bucket,
-	TP_PROTO(struct bch_fs *c, unsigned dev, u64 bucket),
-	TP_ARGS(c, dev, bucket),
+	TP_PROTO(struct bch_fs *c, unsigned dev, u64 bucket, u32 sectors),
+	TP_ARGS(c, dev, bucket, sectors),
 
 	TP_STRUCT__entry(
 		__field(dev_t,		dev			)
 		__field(u32,		dev_idx			)
+		__field(u32,		sectors			)
 		__field(u64,		bucket			)
 	),
 
 	TP_fast_assign(
 		__entry->dev		= c->dev;
 		__entry->dev_idx	= dev;
+		__entry->sectors	= sectors;
 		__entry->bucket		= bucket;
 	),
 
-	TP_printk("%d:%d invalidated %u:%llu",
+	TP_printk("%d:%d invalidated %u:%llu cached sectors %u",
 		  MAJOR(__entry->dev), MINOR(__entry->dev),
-		  __entry->dev_idx, __entry->bucket)
+		  __entry->dev_idx, __entry->bucket,
+		  __entry->sectors)
 );
 
 /* Moving IO */