From: Kent Overstreet <kent.overstreet@linux.dev>
Date: Sun, 4 May 2025 01:26:04 +0000 (-0400)
Subject: bcachefs: bcachefs_metadata_version_fast_device_removal
X-Git-Tag: v6.16-rc1~211^2~88
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a8539ad8fa88e39c3f566b7c35029f25ab90b72e;p=thirdparty%2Flinux.git

bcachefs: bcachefs_metadata_version_fast_device_removal

Fast device removal, that uses backpointers to find pointers to the
device being removed instead of a full metadata scan.

This requires BCH_SB_MEMBER_DELETED_UUID, which is an incompatible
change - hence the version number bump. We don't fully trust
backpointers, so we don't want to reuse device indexes until after a
fsck has verified that there aren't any pointers to removed devices.

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

diff --git a/fs/bcachefs/bcachefs_format.h b/fs/bcachefs/bcachefs_format.h
index 061fa2666f35b..a483d440fa39d 100644
--- a/fs/bcachefs/bcachefs_format.h
+++ b/fs/bcachefs/bcachefs_format.h
@@ -696,7 +696,8 @@ struct bch_sb_field_ext {
 	x(stripe_lru,			BCH_VERSION(1, 23))		\
 	x(casefolding,			BCH_VERSION(1, 24))		\
 	x(extent_flags,			BCH_VERSION(1, 25))		\
-	x(snapshot_deletion_v2,		BCH_VERSION(1, 26))
+	x(snapshot_deletion_v2,		BCH_VERSION(1, 26))		\
+	x(fast_device_removal,		BCH_VERSION(1, 27))
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,
diff --git a/fs/bcachefs/ec.c b/fs/bcachefs/ec.c
index bf5f4f6283a43..c581426e3894a 100644
--- a/fs/bcachefs/ec.c
+++ b/fs/bcachefs/ec.c
@@ -2197,13 +2197,15 @@ static int bch2_invalidate_stripe_to_dev_from_alloc(struct btree_trans *trans, s
 
 int bch2_dev_remove_stripes(struct bch_fs *c, unsigned dev_idx, unsigned flags)
 {
-	return bch2_trans_run(c,
+	int ret = bch2_trans_run(c,
 		for_each_btree_key_max_commit(trans, iter,
 				  BTREE_ID_alloc, POS(dev_idx, 0), POS(dev_idx, U64_MAX),
 				  BTREE_ITER_intent, k,
 				  NULL, NULL, 0, ({
 			bch2_invalidate_stripe_to_dev_from_alloc(trans, k, flags);
 	})));
+	bch_err_fn(c, ret);
+	return ret;
 }
 
 /* startup/shutdown */
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index faa012107a97b..dc8189f9d2f17 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -1726,6 +1726,8 @@ int bch2_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
 {
 	struct bch_member *m;
 	unsigned dev_idx = ca->dev_idx, data;
+	bool fast_device_removal = !bch2_request_incompat_feature(c,
+					bcachefs_metadata_version_fast_device_removal);
 	int ret;
 
 	down_write(&c->state_lock);
@@ -1744,12 +1746,25 @@ int bch2_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
 
 	__bch2_dev_read_only(c, ca);
 
-	ret = bch2_dev_data_drop(c, ca->dev_idx, flags) ?:
-		bch2_dev_remove_stripes(c, ca->dev_idx, flags);
-	bch_err_msg(ca, ret, "bch2_dev_data_drop()");
+	ret = fast_device_removal
+		? bch2_dev_data_drop_by_backpointers(c, ca->dev_idx, flags)
+		: (bch2_dev_data_drop(c, ca->dev_idx, flags) ?:
+		   bch2_dev_remove_stripes(c, ca->dev_idx, flags));
 	if (ret)
 		goto err;
 
+	/* Check if device still has data before blowing away alloc info */
+	struct bch_dev_usage usage = bch2_dev_usage_read(ca);
+	for (unsigned i = 0; i < BCH_DATA_NR; i++)
+		if (!data_type_is_empty(i) &&
+		    !data_type_is_hidden(i) &&
+		    usage.buckets[i]) {
+			bch_err(ca, "Remove failed: still has data (%s, %llu buckets)",
+				__bch2_data_types[i], usage.buckets[i]);
+			ret = -EBUSY;
+			goto err;
+		}
+
 	ret = bch2_dev_remove_alloc(c, ca);
 	bch_err_msg(ca, ret, "bch2_dev_remove_alloc()");
 	if (ret)
@@ -1813,7 +1828,11 @@ int bch2_dev_remove(struct bch_fs *c, struct bch_dev *ca, int flags)
 	 */
 	mutex_lock(&c->sb_lock);
 	m = bch2_members_v2_get_mut(c->disk_sb.sb, dev_idx);
-	memset(&m->uuid, 0, sizeof(m->uuid));
+
+	if (fast_device_removal)
+		m->uuid = BCH_SB_MEMBER_DELETED_UUID;
+	else
+		memset(&m->uuid, 0, sizeof(m->uuid));
 
 	bch2_write_super(c);