bcachefs: Rewrite bch2_bucket_alloc_new_fs()

This changes bch2_bucket_alloc_new_fs() to a simple bump allocator that
doesn't need to use the in memory bucket array, part of a larger patch
series to entirely get rid of the in memory bucket array, except for
gc/fsck.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/alloc_background.c

@@ -513,6 +513,18 @@ static bool bch2_can_invalidate_bucket(struct bch_dev *ca, size_t b,
 	    test_bit(b, ca->buckets_nouse))
 		return false;
 
+	if (ca->new_fs_bucket_idx) {
+		/*
+		 * Device or filesystem is still being initialized, and we
+		 * haven't fully marked superblocks & journal:
+		 */
+		if (is_superblock_bucket(ca, b))
+			return false;
+
+		if (b < ca->new_fs_bucket_idx)
+			return false;
+	}
+
 	gc_gen = bucket_gc_gen(bucket(ca, b));
 
 	ca->inc_gen_needs_gc		+= gc_gen >= BUCKET_GC_GEN_MAX / 2;

fs/bcachefs/alloc_foreground.c

@@ -144,21 +144,15 @@ static void verify_not_stale(struct bch_fs *c, const struct open_buckets *obs)
 /* _only_ for allocating the journal on a new device: */
 long bch2_bucket_alloc_new_fs(struct bch_dev *ca)
 {
-	struct bucket_array *buckets;
-	ssize_t b;
+	while (ca->new_fs_bucket_idx < ca->mi.nbuckets) {
+		u64 b = ca->new_fs_bucket_idx++;
 
-	rcu_read_lock();
-	buckets = bucket_array(ca);
-
-	for (b = buckets->first_bucket; b < buckets->nbuckets; b++)
-		if (is_available_bucket(buckets->b[b].mark) &&
-		    (!ca->buckets_nouse || !test_bit(b, ca->buckets_nouse)) &&
-		    !buckets->b[b].mark.owned_by_allocator)
-			goto success;
-	b = -1;
-success:
-	rcu_read_unlock();
+		if (!is_superblock_bucket(ca, b) &&
+		    (!ca->buckets_nouse || !test_bit(b, ca->buckets_nouse)))
 			return b;
+	}
+
+	return -1;
 }
 
 static inline unsigned open_buckets_reserved(enum alloc_reserve reserve)

fs/bcachefs/bcachefs.h

@@ -453,6 +453,7 @@ struct bch_dev {
 	struct bch_dev_usage __percpu	*usage_gc;
 
 	/* Allocator: */
+	u64			new_fs_bucket_idx;
 	struct task_struct __rcu *alloc_thread;
 
 	/*

fs/bcachefs/recovery.c

@@ -1429,6 +1429,8 @@ int bch2_fs_initialize(struct bch_fs *c)
 			percpu_ref_put(&ca->ref);
 			goto err;
 		}
+
+		ca->new_fs_bucket_idx = 0;
 	}
 
 	err = "error creating root snapshot node";

fs/bcachefs/super.c

@@ -1726,6 +1726,8 @@ int bch2_dev_add(struct bch_fs *c, const char *path)
 	if (ret)
 		goto err_late;
 
+	ca->new_fs_bucket_idx = 0;
+
 	if (ca->mi.state == BCH_MEMBER_STATE_rw) {
 		ret = __bch2_dev_read_write(c, ca);
 		if (ret)

fs/bcachefs/super.h

@@ -194,6 +194,27 @@ static inline struct bch_devs_mask bch2_online_devs(struct bch_fs *c)
 	return devs;
 }
 
+static inline bool is_superblock_bucket(struct bch_dev *ca, u64 b)
+{
+	struct bch_sb_layout *layout = &ca->disk_sb.sb->layout;
+	u64 b_offset	= bucket_to_sector(ca, b);
+	u64 b_end	= bucket_to_sector(ca, b + 1);
+	unsigned i;
+
+	if (!b)
+		return true;
+
+	for (i = 0; i < layout->nr_superblocks; i++) {
+		u64 offset = le64_to_cpu(layout->sb_offset[i]);
+		u64 end = offset + (1 << layout->sb_max_size_bits);
+
+		if (!(offset >= b_end || end <= b_offset))
+			return true;
+	}
+
+	return false;
+}
+
 struct bch_fs *bch2_dev_to_fs(dev_t);
 struct bch_fs *bch2_uuid_to_fs(__uuid_t);