bcachefs: bucket_gens btree

To improve mount times, add a btree for just bucket gens, 256 of them
per key: this means we'll have to scan drastically less metadata at
startup.

This adds
 - trigger for keeping it in sync with the all btree
 - initialization code, for filesystems from previous versions
 - new path for reading bucket gens
 - new fsck code

And a new on disk format version.

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

1 files changed, 14 insertions, 1 deletions

diff --git a/fs/bcachefs/recovery.c b/fs/bcachefs/recovery.c
index b35590226037..b10ba8963350 100644
--- a/fs/bcachefs/recovery.c
+++ b/fs/bcachefs/recovery.c
@@ -929,6 +929,7 @@ static bool btree_id_is_alloc(enum btree_id id)
 	case BTREE_ID_backpointers:
 	case BTREE_ID_need_discard:
 	case BTREE_ID_freespace:
+	case BTREE_ID_bucket_gens:
 		return true;
 	default:
 		return false;
@@ -1237,7 +1238,9 @@ use_clean:
 	err = "error reading allocation information";
 
 	down_read(&c->gc_lock);
-	ret = bch2_alloc_read(c);
+	ret = c->sb.version < bcachefs_metadata_version_bucket_gens
+		? bch2_alloc_read(c)
+		: bch2_bucket_gens_read(c);
 	up_read(&c->gc_lock);
 
 	if (ret)
@@ -1362,6 +1365,16 @@ use_clean:
 	if (ret)
 		goto err;
 
+	if (c->sb.version < bcachefs_metadata_version_bucket_gens &&
+	    c->opts.version_upgrade) {
+		bch_info(c, "initializing bucket_gens");
+		err = "error initializing bucket gens";
+		ret = bch2_bucket_gens_init(c);
+		if (ret)
+			goto err;
+		bch_verbose(c, "bucket_gens init done");
+	}
+
 	if (c->sb.version < bcachefs_metadata_version_snapshot_2) {
 		/* set bi_subvol on root inode */
 		err = "error upgrade root inode for subvolumes";