diff --git a/.bcachefs_revision b/.bcachefs_revision
index 280ed22c..b5a8d6b1 100644
--- a/.bcachefs_revision
+++ b/.bcachefs_revision
@@ -1 +1 @@
-c76f7e91e8939751ccc96ca2f8f6bfe6dd368d93
+2f4e24d85692600a698d78938a213f27593bda25
diff --git a/libbcachefs/alloc_background.c b/libbcachefs/alloc_background.c
index 288018fb..359cb23f 100644
--- a/libbcachefs/alloc_background.c
+++ b/libbcachefs/alloc_background.c
@@ -2,6 +2,7 @@
 #include "bcachefs.h"
 #include "alloc_background.h"
 #include "alloc_foreground.h"
+#include "backpointers.h"
 #include "btree_cache.h"
 #include "btree_io.h"
 #include "btree_key_cache.h"
@@ -37,8 +38,6 @@ static const unsigned BCH_ALLOC_V1_FIELD_BYTES[] = {
 
 struct bkey_alloc_unpacked {
 	u64		journal_seq;
-	u64		bucket;
-	u8		dev;
 	u8		gen;
 	u8		oldest_gen;
 	u8		data_type;
@@ -194,11 +193,7 @@ static int bch2_alloc_unpack_v3(struct bkey_alloc_unpacked *out,
 
 static struct bkey_alloc_unpacked bch2_alloc_unpack(struct bkey_s_c k)
 {
-	struct bkey_alloc_unpacked ret = {
-		.dev	= k.k->p.inode,
-		.bucket	= k.k->p.offset,
-		.gen	= 0,
-	};
+	struct bkey_alloc_unpacked ret = { .gen	= 0 };
 
 	switch (k.k->type) {
 	case KEY_TYPE_alloc:
@@ -215,48 +210,6 @@ static struct bkey_alloc_unpacked bch2_alloc_unpack(struct bkey_s_c k)
 	return ret;
 }
 
-void bch2_alloc_to_v4(struct bkey_s_c k, struct bch_alloc_v4 *out)
-{
-	if (k.k->type == KEY_TYPE_alloc_v4) {
-		*out = *bkey_s_c_to_alloc_v4(k).v;
-	} else {
-		struct bkey_alloc_unpacked u = bch2_alloc_unpack(k);
-
-		*out = (struct bch_alloc_v4) {
-			.journal_seq		= u.journal_seq,
-			.flags			= u.need_discard,
-			.gen			= u.gen,
-			.oldest_gen		= u.oldest_gen,
-			.data_type		= u.data_type,
-			.stripe_redundancy	= u.stripe_redundancy,
-			.dirty_sectors		= u.dirty_sectors,
-			.cached_sectors		= u.cached_sectors,
-			.io_time[READ]		= u.read_time,
-			.io_time[WRITE]		= u.write_time,
-			.stripe			= u.stripe,
-		};
-	}
-}
-
-struct bkey_i_alloc_v4 *bch2_alloc_to_v4_mut(struct btree_trans *trans, struct bkey_s_c k)
-{
-	struct bkey_i_alloc_v4 *ret;
-
-	if (k.k->type == KEY_TYPE_alloc_v4) {
-		ret = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
-		if (!IS_ERR(ret))
-			bkey_reassemble(&ret->k_i, k);
-	} else {
-		ret = bch2_trans_kmalloc(trans, sizeof(*ret));
-		if (!IS_ERR(ret)) {
-			bkey_alloc_v4_init(&ret->k_i);
-			ret->k.p = k.k->p;
-			bch2_alloc_to_v4(k, &ret->v);
-		}
-	}
-	return ret;
-}
-
 struct bkey_i_alloc_v4 *
 bch2_trans_start_alloc_update(struct btree_trans *trans, struct btree_iter *iter,
 			      struct bpos pos)
@@ -339,9 +292,15 @@ int bch2_alloc_v4_invalid(const struct bch_fs *c, struct bkey_s_c k,
 {
 	struct bkey_s_c_alloc_v4 a = bkey_s_c_to_alloc_v4(k);
 
-	if (bkey_val_bytes(k.k) != sizeof(struct bch_alloc_v4)) {
-		prt_printf(err, "bad val size (%zu != %zu)",
-		       bkey_val_bytes(k.k), sizeof(struct bch_alloc_v4));
+	if (alloc_v4_u64s(a.v) != bkey_val_u64s(k.k)) {
+		prt_printf(err, "bad val size (%lu != %u)",
+		       bkey_val_u64s(k.k), alloc_v4_u64s(a.v));
+		return -EINVAL;
+	}
+
+	if (!BCH_ALLOC_V4_BACKPOINTERS_START(a.v) &&
+	    BCH_ALLOC_V4_NR_BACKPOINTERS(a.v)) {
+		prt_printf(err, "invalid backpointers_start");
 		return -EINVAL;
 	}
 
@@ -401,9 +360,19 @@ int bch2_alloc_v4_invalid(const struct bch_fs *c, struct bkey_s_c k,
 	return 0;
 }
 
+static inline u64 swab40(u64 x)
+{
+	return (((x & 0x00000000ffULL) << 32)|
+		((x & 0x000000ff00ULL) << 16)|
+		((x & 0x0000ff0000ULL) >>  0)|
+		((x & 0x00ff000000ULL) >> 16)|
+		((x & 0xff00000000ULL) >> 32));
+}
+
 void bch2_alloc_v4_swab(struct bkey_s k)
 {
 	struct bch_alloc_v4 *a = bkey_s_to_alloc_v4(k).v;
+	struct bch_backpointer *bp, *bps;
 
 	a->journal_seq		= swab64(a->journal_seq);
 	a->flags		= swab32(a->flags);
@@ -413,25 +382,135 @@ void bch2_alloc_v4_swab(struct bkey_s k)
 	a->io_time[1]		= swab64(a->io_time[1]);
 	a->stripe		= swab32(a->stripe);
 	a->nr_external_backpointers = swab32(a->nr_external_backpointers);
+
+	bps = alloc_v4_backpointers(a);
+	for (bp = bps; bp < bps + BCH_ALLOC_V4_NR_BACKPOINTERS(a); bp++) {
+		bp->bucket_offset	= swab40(bp->bucket_offset);
+		bp->bucket_len		= swab32(bp->bucket_len);
+		bch2_bpos_swab(&bp->pos);
+	}
 }
 
 void bch2_alloc_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
 {
-	struct bch_alloc_v4 a;
+	struct bch_alloc_v4 _a;
+	const struct bch_alloc_v4 *a = &_a;
+	const struct bch_backpointer *bps;
+	unsigned i;
 
-	bch2_alloc_to_v4(k, &a);
+	if (k.k->type == KEY_TYPE_alloc_v4)
+		a = bkey_s_c_to_alloc_v4(k).v;
+	else
+		bch2_alloc_to_v4(k, &_a);
 
-	prt_printf(out, "gen %u oldest_gen %u data_type %s journal_seq %llu need_discard %llu need_inc_gen %llu",
-	       a.gen, a.oldest_gen, bch2_data_types[a.data_type],
-	       a.journal_seq,
-	       BCH_ALLOC_V4_NEED_DISCARD(&a),
-	       BCH_ALLOC_V4_NEED_INC_GEN(&a));
-	prt_printf(out, " dirty_sectors %u",	a.dirty_sectors);
-	prt_printf(out, " cached_sectors %u",	a.cached_sectors);
-	prt_printf(out, " stripe %u",		a.stripe);
-	prt_printf(out, " stripe_redundancy %u",	a.stripe_redundancy);
-	prt_printf(out, " read_time %llu",		a.io_time[READ]);
-	prt_printf(out, " write_time %llu",		a.io_time[WRITE]);
+	prt_newline(out);
+	printbuf_indent_add(out, 2);
+
+	prt_printf(out, "gen %u oldest_gen %u data_type %s",
+	       a->gen, a->oldest_gen, bch2_data_types[a->data_type]);
+	prt_newline(out);
+	prt_printf(out, "journal_seq       %llu",	a->journal_seq);
+	prt_newline(out);
+	prt_printf(out, "need_discard      %llu",	BCH_ALLOC_V4_NEED_DISCARD(a));
+	prt_newline(out);
+	prt_printf(out, "need_inc_gen      %llu",	BCH_ALLOC_V4_NEED_INC_GEN(a));
+	prt_newline(out);
+	prt_printf(out, "dirty_sectors     %u",	a->dirty_sectors);
+	prt_newline(out);
+	prt_printf(out, "cached_sectors    %u",	a->cached_sectors);
+	prt_newline(out);
+	prt_printf(out, "stripe            %u",	a->stripe);
+	prt_newline(out);
+	prt_printf(out, "stripe_redundancy %u",	a->stripe_redundancy);
+	prt_newline(out);
+	prt_printf(out, "io_time[READ]     %llu",	a->io_time[READ]);
+	prt_newline(out);
+	prt_printf(out, "io_time[WRITE]    %llu",	a->io_time[WRITE]);
+	prt_newline(out);
+	prt_printf(out, "backpointers:     %llu",	BCH_ALLOC_V4_NR_BACKPOINTERS(a));
+	printbuf_indent_add(out, 2);
+
+	bps = alloc_v4_backpointers_c(a);
+	for (i = 0; i < BCH_ALLOC_V4_NR_BACKPOINTERS(a); i++) {
+		prt_newline(out);
+		bch2_backpointer_to_text(out, &bps[i]);
+	}
+
+	printbuf_indent_sub(out, 4);
+}
+
+void bch2_alloc_to_v4(struct bkey_s_c k, struct bch_alloc_v4 *out)
+{
+	if (k.k->type == KEY_TYPE_alloc_v4) {
+		int d;
+
+		*out = *bkey_s_c_to_alloc_v4(k).v;
+
+		d = (int) BCH_ALLOC_V4_U64s -
+			(int) (BCH_ALLOC_V4_BACKPOINTERS_START(out) ?: BCH_ALLOC_V4_U64s_V0);
+		if (unlikely(d > 0)) {
+			memset((u64 *) out + BCH_ALLOC_V4_BACKPOINTERS_START(out),
+			       0,
+			       d * sizeof(u64));
+			SET_BCH_ALLOC_V4_BACKPOINTERS_START(out, BCH_ALLOC_V4_U64s);
+		}
+	} else {
+		struct bkey_alloc_unpacked u = bch2_alloc_unpack(k);
+
+		*out = (struct bch_alloc_v4) {
+			.journal_seq		= u.journal_seq,
+			.flags			= u.need_discard,
+			.gen			= u.gen,
+			.oldest_gen		= u.oldest_gen,
+			.data_type		= u.data_type,
+			.stripe_redundancy	= u.stripe_redundancy,
+			.dirty_sectors		= u.dirty_sectors,
+			.cached_sectors		= u.cached_sectors,
+			.io_time[READ]		= u.read_time,
+			.io_time[WRITE]		= u.write_time,
+			.stripe			= u.stripe,
+		};
+
+		SET_BCH_ALLOC_V4_BACKPOINTERS_START(out, BCH_ALLOC_V4_U64s);
+	}
+}
+
+struct bkey_i_alloc_v4 *bch2_alloc_to_v4_mut(struct btree_trans *trans, struct bkey_s_c k)
+{
+	unsigned bytes = k.k->type == KEY_TYPE_alloc_v4
+		? bkey_bytes(k.k)
+		: sizeof(struct bkey_i_alloc_v4);
+	struct bkey_i_alloc_v4 *ret;
+
+	/*
+	 * Reserve space for one more backpointer here:
+	 * Not sketchy at doing it this way, nope...
+	 */
+	ret = bch2_trans_kmalloc(trans, bytes + sizeof(struct bch_backpointer));
+	if (IS_ERR(ret))
+		return ret;
+
+	if (k.k->type == KEY_TYPE_alloc_v4) {
+		bkey_reassemble(&ret->k_i, k);
+
+		if (BCH_ALLOC_V4_BACKPOINTERS_START(&ret->v) < BCH_ALLOC_V4_U64s) {
+			struct bch_backpointer *src, *dst;
+
+			src = alloc_v4_backpointers(&ret->v);
+			SET_BCH_ALLOC_V4_BACKPOINTERS_START(&ret->v, BCH_ALLOC_V4_U64s);
+			dst = alloc_v4_backpointers(&ret->v);
+
+			memmove(dst, src, BCH_ALLOC_V4_NR_BACKPOINTERS(&ret->v) *
+				sizeof(struct bch_backpointer));
+			memset(src, 0, dst - src);
+			set_alloc_v4_u64s(ret);
+		}
+	} else {
+		bkey_alloc_v4_init(&ret->k_i);
+		ret->k.p = k.k->p;
+		bch2_alloc_to_v4(k, &ret->v);
+	}
+	return ret;
 }
 
 int bch2_alloc_read(struct bch_fs *c)
@@ -1052,6 +1131,7 @@ static void bch2_do_discards_work(struct work_struct *work)
 		if (ret)
 			break;
 
+		this_cpu_inc(c->counters[BCH_COUNTER_bucket_discard]);
 		discarded++;
 	}
 	bch2_trans_iter_exit(&trans, &iter);
diff --git a/libbcachefs/alloc_background.h b/libbcachefs/alloc_background.h
index ff366e61..2ac6b504 100644
--- a/libbcachefs/alloc_background.h
+++ b/libbcachefs/alloc_background.h
@@ -70,6 +70,22 @@ static inline struct bpos alloc_freespace_pos(struct bpos pos, struct bch_alloc_
 	return pos;
 }
 
+static inline unsigned alloc_v4_u64s(const struct bch_alloc_v4 *a)
+{
+	unsigned ret = (BCH_ALLOC_V4_BACKPOINTERS_START(a) ?:
+			BCH_ALLOC_V4_U64s_V0) +
+		BCH_ALLOC_V4_NR_BACKPOINTERS(a) *
+		(sizeof(struct bch_backpointer) / sizeof(u64));
+
+	BUG_ON(ret > U8_MAX - BKEY_U64s);
+	return ret;
+}
+
+static inline void set_alloc_v4_u64s(struct bkey_i_alloc_v4 *a)
+{
+	set_bkey_val_u64s(&a->k, alloc_v4_u64s(&a->v));
+}
+
 struct bkey_i_alloc_v4 *
 bch2_trans_start_alloc_update(struct btree_trans *, struct btree_iter *, struct bpos);
 
@@ -143,6 +159,16 @@ static inline u64 should_invalidate_buckets(struct bch_dev *ca,
 
 void bch2_do_invalidates(struct bch_fs *);
 
+static inline struct bch_backpointer *alloc_v4_backpointers(struct bch_alloc_v4 *a)
+{
+	return (void *) ((u64 *) &a->v + BCH_ALLOC_V4_BACKPOINTERS_START(a));
+}
+
+static inline const struct bch_backpointer *alloc_v4_backpointers_c(const struct bch_alloc_v4 *a)
+{
+	return (void *) ((u64 *) &a->v + BCH_ALLOC_V4_BACKPOINTERS_START(a));
+}
+
 int bch2_fs_freespace_init(struct bch_fs *);
 
 void bch2_recalc_capacity(struct bch_fs *);
diff --git a/libbcachefs/alloc_foreground.c b/libbcachefs/alloc_foreground.c
index d52282fb..7a878a69 100644
--- a/libbcachefs/alloc_foreground.c
+++ b/libbcachefs/alloc_foreground.c
@@ -506,7 +506,7 @@ struct open_bucket *bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
 	int ret;
 again:
 	usage = bch2_dev_usage_read(ca);
-	avail = __dev_buckets_available(ca, usage,reserve);
+	avail = dev_buckets_free(ca, usage,reserve);
 
 	if (usage.d[BCH_DATA_need_discard].buckets > avail)
 		bch2_do_discards(c);
diff --git a/libbcachefs/backpointers.c b/libbcachefs/backpointers.c
new file mode 100644
index 00000000..f3260bbe
--- /dev/null
+++ b/libbcachefs/backpointers.c
@@ -0,0 +1,891 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "bcachefs.h"
+#include "alloc_background.h"
+#include "backpointers.h"
+#include "btree_cache.h"
+#include "btree_update.h"
+#include "error.h"
+
+#define MAX_EXTENT_COMPRESS_RATIO_SHIFT		10
+
+/*
+ * Convert from pos in backpointer btree to pos of corresponding bucket in alloc
+ * btree:
+ */
+static inline struct bpos bp_pos_to_bucket(const struct bch_fs *c,
+					   struct bpos bp_pos)
+{
+	struct bch_dev *ca = bch_dev_bkey_exists(c, bp_pos.inode);
+	u64 bucket_sector = bp_pos.offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT;
+
+	return POS(bp_pos.inode, sector_to_bucket(ca, bucket_sector));
+}
+
+/*
+ * Convert from pos in alloc btree + bucket offset to pos in backpointer btree:
+ */
+static inline struct bpos bucket_pos_to_bp(const struct bch_fs *c,
+					   struct bpos bucket,
+					   u64 bucket_offset)
+{
+	struct bch_dev *ca = bch_dev_bkey_exists(c, bucket.inode);
+
+	return POS(bucket.inode,
+		   (bucket_to_sector(ca, bucket.offset) <<
+		    MAX_EXTENT_COMPRESS_RATIO_SHIFT) + bucket_offset);
+}
+
+void bch2_extent_ptr_to_bp(struct bch_fs *c,
+			   enum btree_id btree_id, unsigned level,
+			   struct bkey_s_c k, struct extent_ptr_decoded p,
+			   struct bpos *bucket_pos, struct bch_backpointer *bp)
+{
+	enum bch_data_type data_type = level ? BCH_DATA_btree : BCH_DATA_user;
+	s64 sectors = level ? btree_sectors(c) : k.k->size;
+	u32 bucket_offset;
+
+	*bucket_pos = PTR_BUCKET_POS_OFFSET(c, &p.ptr, &bucket_offset);
+	*bp = (struct bch_backpointer) {
+		.btree_id	= btree_id,
+		.level		= level,
+		.data_type	= data_type,
+		.bucket_offset	= ((u64) bucket_offset << MAX_EXTENT_COMPRESS_RATIO_SHIFT) +
+			p.crc.offset,
+		.bucket_len	= ptr_disk_sectors(sectors, p),
+		.pos		= k.k->p,
+	};
+}
+
+static bool extent_matches_bp(struct bch_fs *c,
+			      enum btree_id btree_id, unsigned level,
+			      struct bkey_s_c k,
+			      struct bpos bucket,
+			      struct bch_backpointer bp)
+{
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	const union bch_extent_entry *entry;
+	struct extent_ptr_decoded p;
+
+	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
+		struct bpos bucket2;
+		struct bch_backpointer bp2;
+
+		if (p.ptr.cached)
+			continue;
+
+		bch2_extent_ptr_to_bp(c, btree_id, level, k, p,
+				      &bucket2, &bp2);
+		if (!bpos_cmp(bucket, bucket2) &&
+		    !memcmp(&bp, &bp2, sizeof(bp)))
+			return true;
+	}
+
+	return false;
+}
+
+int bch2_backpointer_invalid(const struct bch_fs *c, struct bkey_s_c k,
+			     int rw, struct printbuf *err)
+{
+	struct bkey_s_c_backpointer bp = bkey_s_c_to_backpointer(k);
+	struct bpos bucket = bp_pos_to_bucket(c, bp.k->p);
+
+	if (bkey_val_bytes(bp.k) < sizeof(*bp.v)) {
+		prt_str(err, "incorrect value size");
+		return -EINVAL;
+	}
+
+	if (bpos_cmp(bp.k->p, bucket_pos_to_bp(c, bucket, bp.v->bucket_offset))) {
+		prt_str(err, "backpointer at wrong pos");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+void bch2_backpointer_to_text(struct printbuf *out, const struct bch_backpointer *bp)
+{
+	prt_printf(out, "btree=%s l=%u offset=%llu:%u len=%u pos=",
+	       bch2_btree_ids[bp->btree_id],
+	       bp->level,
+	       (u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
+	       (u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
+	       bp->bucket_len);
+	bch2_bpos_to_text(out, bp->pos);
+}
+
+void bch2_backpointer_k_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
+{
+	bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
+}
+
+void bch2_backpointer_swab(struct bkey_s k)
+{
+	struct bkey_s_backpointer bp = bkey_s_to_backpointer(k);
+
+	bp.v->bucket_offset	= swab32(bp.v->bucket_offset);
+	bp.v->bucket_len	= swab32(bp.v->bucket_len);
+	bch2_bpos_swab(&bp.v->pos);
+}
+
+#define BACKPOINTER_OFFSET_MAX	((1ULL << 40) - 1)
+
+static inline int backpointer_cmp(struct bch_backpointer l, struct bch_backpointer r)
+{
+	return cmp_int(l.bucket_offset, r.bucket_offset);
+}
+
+static int bch2_backpointer_del_by_offset(struct btree_trans *trans,
+					  struct bpos bucket,
+					  u64 bp_offset,
+					  struct bch_backpointer bp)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	if (bp_offset < BACKPOINTER_OFFSET_MAX) {
+		struct bch_backpointer *bps;
+		struct bkey_i_alloc_v4 *a;
+		unsigned i, nr;
+
+		bch2_trans_iter_init(trans, &iter, BTREE_ID_alloc,
+				     bucket,
+				     BTREE_ITER_INTENT|
+				     BTREE_ITER_SLOTS|
+				     BTREE_ITER_WITH_UPDATES);
+		k = bch2_btree_iter_peek_slot(&iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+
+		if (k.k->type != KEY_TYPE_alloc_v4) {
+			ret = -ENOENT;
+			goto err;
+		}
+
+		a = bch2_alloc_to_v4_mut(trans, k);
+		ret = PTR_ERR_OR_ZERO(a);
+		if (ret)
+			goto err;
+		bps = alloc_v4_backpointers(&a->v);
+		nr = BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v);
+
+		for (i = 0; i < nr; i++) {
+			if (bps[i].bucket_offset == bp_offset)
+				goto found;
+			if (bps[i].bucket_offset > bp_offset)
+				break;
+		}
+
+		ret = -ENOENT;
+		goto err;
+found:
+		if (memcmp(&bps[i], &bp, sizeof(bp))) {
+			ret = -ENOENT;
+			goto err;
+		}
+		array_remove_item(bps, nr, i);
+		SET_BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v, nr);
+		set_alloc_v4_u64s(a);
+		ret = bch2_trans_update(trans, &iter, &a->k_i, 0);
+	} else {
+		bp_offset -= BACKPOINTER_OFFSET_MAX;
+
+		bch2_trans_iter_init(trans, &iter, BTREE_ID_backpointers,
+				     bucket_pos_to_bp(c, bucket, bp_offset),
+				     BTREE_ITER_INTENT|
+				     BTREE_ITER_SLOTS|
+				     BTREE_ITER_WITH_UPDATES);
+		k = bch2_btree_iter_peek_slot(&iter);
+		ret = bkey_err(k);
+		if (ret)
+			goto err;
+
+		if (k.k->type != KEY_TYPE_backpointer ||
+		    memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp))) {
+			ret = -ENOENT;
+			goto err;
+		}
+
+		ret = bch2_btree_delete_at(trans, &iter, 0);
+	}
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+int bch2_bucket_backpointer_del(struct btree_trans *trans,
+				struct bkey_i_alloc_v4 *a,
+				struct bch_backpointer bp,
+				struct bkey_s_c orig_k)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_backpointer *bps = alloc_v4_backpointers(&a->v);
+	unsigned i, nr = BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v);
+	struct btree_iter bp_iter;
+	struct bkey_s_c k;
+	int ret;
+
+	for (i = 0; i < nr; i++) {
+		int cmp = backpointer_cmp(bps[i], bp) ?:
+			memcmp(&bps[i], &bp, sizeof(bp));
+		if (!cmp)
+			goto found;
+		if (cmp >= 0)
+			break;
+	}
+
+	goto btree;
+found:
+	array_remove_item(bps, nr, i);
+	SET_BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v, nr);
+	set_alloc_v4_u64s(a);
+	return 0;
+btree:
+	bch2_trans_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
+			     bucket_pos_to_bp(c, a->k.p, bp.bucket_offset),
+			     BTREE_ITER_INTENT|
+			     BTREE_ITER_SLOTS|
+			     BTREE_ITER_WITH_UPDATES);
+	k = bch2_btree_iter_peek_slot(&bp_iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type != KEY_TYPE_backpointer ||
+	    memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp))) {
+		struct printbuf buf = PRINTBUF;
+
+		prt_printf(&buf, "backpointer not found when deleting");
+		prt_newline(&buf);
+		printbuf_indent_add(&buf, 2);
+
+		prt_printf(&buf, "searching for ");
+		bch2_backpointer_to_text(&buf, &bp);
+		prt_newline(&buf);
+
+		prt_printf(&buf, "got ");
+		bch2_bkey_val_to_text(&buf, c, k);
+		prt_newline(&buf);
+
+		prt_str(&buf, "alloc ");
+		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&a->k_i));
+		prt_newline(&buf);
+
+		prt_printf(&buf, "for ");
+		bch2_bkey_val_to_text(&buf, c, orig_k);
+
+		if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags)) {
+			bch_err(c, "%s", buf.buf);
+		} else {
+			ret = -EIO;
+			bch2_trans_inconsistent(trans, "%s", buf.buf);
+		}
+		printbuf_exit(&buf);
+		goto err;
+	}
+
+	ret = bch2_btree_delete_at(trans, &bp_iter, 0);
+err:
+	bch2_trans_iter_exit(trans, &bp_iter);
+	return ret;
+}
+
+int bch2_bucket_backpointer_add(struct btree_trans *trans,
+				struct bkey_i_alloc_v4 *a,
+				struct bch_backpointer bp,
+				struct bkey_s_c orig_k)
+{
+	struct bch_fs *c = trans->c;
+	struct bch_dev *ca;
+	struct bch_backpointer *bps = alloc_v4_backpointers(&a->v);
+	unsigned i, nr = BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v);
+	struct bkey_i_backpointer *bp_k;
+	struct btree_iter bp_iter;
+	struct bkey_s_c k;
+	int ret;
+
+	/* Check for duplicates: */
+	for (i = 0; i < nr; i++) {
+		int cmp = backpointer_cmp(bps[i], bp);
+		if (cmp >= 0)
+			break;
+	}
+
+	if ((i &&
+	     (bps[i - 1].bucket_offset +
+	      bps[i - 1].bucket_len > bp.bucket_offset)) ||
+	    (i < nr &&
+	     (bp.bucket_offset + bp.bucket_len > bps[i].bucket_offset))) {
+		struct printbuf buf = PRINTBUF;
+
+		prt_printf(&buf, "overlapping backpointer found when inserting ");
+		bch2_backpointer_to_text(&buf, &bp);
+		prt_newline(&buf);
+		printbuf_indent_add(&buf, 2);
+
+		prt_printf(&buf, "into ");
+		bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&a->k_i));
+		prt_newline(&buf);
+
+		prt_printf(&buf, "for ");
+		bch2_bkey_val_to_text(&buf, c, orig_k);
+
+		if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags))
+			bch_err(c, "%s", buf.buf);
+		else {
+			bch2_trans_inconsistent(trans, "%s", buf.buf);
+			printbuf_exit(&buf);
+			return -EIO;
+		}
+	}
+
+	if (nr < BCH_ALLOC_V4_NR_BACKPOINTERS_MAX) {
+		array_insert_item(bps, nr, i, bp);
+		SET_BCH_ALLOC_V4_NR_BACKPOINTERS(&a->v, nr);
+		set_alloc_v4_u64s(a);
+		return 0;
+	}
+
+	/* Overflow: use backpointer btree */
+	bp_k = bch2_trans_kmalloc(trans, sizeof(*bp_k));
+	ret = PTR_ERR_OR_ZERO(bp_k);
+	if (ret)
+		return ret;
+
+	ca = bch_dev_bkey_exists(c, a->k.p.inode);
+
+	bkey_backpointer_init(&bp_k->k_i);
+	bp_k->k.p = bucket_pos_to_bp(c, a->k.p, bp.bucket_offset);
+	bp_k->v = bp;
+
+	bch2_trans_iter_init(trans, &bp_iter, BTREE_ID_backpointers, bp_k->k.p,
+			     BTREE_ITER_INTENT|
+			     BTREE_ITER_SLOTS|
+			     BTREE_ITER_WITH_UPDATES);
+	k = bch2_btree_iter_peek_slot(&bp_iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto err;
+
+	if (k.k->type) {
+		struct printbuf buf = PRINTBUF;
+
+		prt_printf(&buf, "existing btree backpointer key found when inserting ");
+		bch2_backpointer_to_text(&buf, &bp);
+		prt_newline(&buf);
+		printbuf_indent_add(&buf, 2);
+
+		prt_printf(&buf, "found ");
+		bch2_bkey_val_to_text(&buf, c, k);
+		prt_newline(&buf);
+
+		prt_printf(&buf, "for ");
+		bch2_bkey_val_to_text(&buf, c, orig_k);
+
+		if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags))
+			bch_err(c, "%s", buf.buf);
+		else {
+			bch2_trans_inconsistent(trans, "%s", buf.buf);
+			printbuf_exit(&buf);
+			ret = -EIO;
+			goto err;
+		}
+	}
+
+	ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
+err:
+	bch2_trans_iter_exit(trans, &bp_iter);
+	return ret;
+}
+
+/*
+ * Find the next backpointer >= *bp_offset:
+ */
+int bch2_get_next_backpointer(struct btree_trans *trans,
+			      struct bpos bucket, int gen,
+			      u64 *bp_offset,
+			      struct bch_backpointer *dst)
+{
+	struct bch_fs *c = trans->c;
+	struct bpos bp_pos =
+		bucket_pos_to_bp(c, bucket,
+				max(*bp_offset, BACKPOINTER_OFFSET_MAX) - BACKPOINTER_OFFSET_MAX);
+	struct bpos bp_end_pos =
+		bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
+	struct btree_iter alloc_iter, bp_iter = { NULL };
+	struct bkey_s_c k;
+	struct bkey_s_c_alloc_v4 a;
+	size_t i;
+	int ret;
+
+	bch2_trans_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
+			     bucket, BTREE_ITER_CACHED);
+	k = bch2_btree_iter_peek_slot(&alloc_iter);
+	ret = bkey_err(k);
+	if (ret)
+		goto out;
+
+	if (k.k->type != KEY_TYPE_alloc_v4)
+		goto done;
+
+	a = bkey_s_c_to_alloc_v4(k);
+	if (gen >= 0 && a.v->gen != gen)
+		goto done;
+
+	for (i = 0; i < BCH_ALLOC_V4_NR_BACKPOINTERS(a.v); i++) {
+		if (alloc_v4_backpointers_c(a.v)[i].bucket_offset < *bp_offset)
+			continue;
+
+		*dst = alloc_v4_backpointers_c(a.v)[i];
+		*bp_offset = dst->bucket_offset;
+		goto out;
+	}
+
+	for_each_btree_key(trans, bp_iter, BTREE_ID_backpointers,
+			   bp_pos, 0, k, ret) {
+		if (bpos_cmp(k.k->p, bp_end_pos) >= 0)
+			break;
+
+		if (k.k->type != KEY_TYPE_backpointer)
+			continue;
+
+		*dst = *bkey_s_c_to_backpointer(k).v;
+		*bp_offset = dst->bucket_offset + BACKPOINTER_OFFSET_MAX;
+		goto out;
+	}
+done:
+	*bp_offset = U64_MAX;
+out:
+	bch2_trans_iter_exit(trans, &bp_iter);
+	bch2_trans_iter_exit(trans, &alloc_iter);
+	return ret;
+}
+
+static void backpointer_not_found(struct btree_trans *trans,
+				  struct bpos bucket,
+				  u64 bp_offset,
+				  struct bch_backpointer bp,
+				  struct bkey_s_c k,
+				  const char *thing_it_points_to)
+{
+	struct bch_fs *c = trans->c;
+	struct printbuf buf = PRINTBUF;
+
+	prt_printf(&buf, "backpointer doesn't match %s it points to:\n  ",
+		   thing_it_points_to);
+	prt_printf(&buf, "bucket: ");
+	bch2_bpos_to_text(&buf, bucket);
+	prt_printf(&buf, "\n  ");
+
+	if (bp_offset >= BACKPOINTER_OFFSET_MAX) {
+		struct bpos bp_pos =
+			bucket_pos_to_bp(c, bucket,
+					bp_offset - BACKPOINTER_OFFSET_MAX);
+		prt_printf(&buf, "backpointer pos: ");
+		bch2_bpos_to_text(&buf, bp_pos);
+		prt_printf(&buf, "\n  ");
+	}
+
+	bch2_backpointer_to_text(&buf, &bp);
+	prt_printf(&buf, "\n  ");
+	bch2_bkey_val_to_text(&buf, c, k);
+	if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags))
+		bch_err(c, "%s", buf.buf);
+	else
+		bch2_trans_inconsistent(trans, "%s", buf.buf);
+
+	printbuf_exit(&buf);
+}
+
+struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *trans,
+					 struct btree_iter *iter,
+					 struct bpos bucket,
+					 u64 bp_offset,
+					 struct bch_backpointer bp)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_s_c k;
+
+	bch2_trans_node_iter_init(trans, iter,
+				  bp.btree_id,
+				  bp.pos,
+				  0,
+				  min(bp.level, c->btree_roots[bp.btree_id].level),
+				  0);
+	k = bch2_btree_iter_peek_slot(iter);
+	if (bkey_err(k)) {
+		bch2_trans_iter_exit(trans, iter);
+		return k;
+	}
+
+	if (bp.level == c->btree_roots[bp.btree_id].level + 1)
+		k = bkey_i_to_s_c(&c->btree_roots[bp.btree_id].key);
+
+	if (extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
+		return k;
+
+	backpointer_not_found(trans, bucket, bp_offset, bp, k, "extent");
+
+	bch2_trans_iter_exit(trans, iter);
+	return bkey_s_c_null;
+}
+
+struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
+					struct btree_iter *iter,
+					struct bpos bucket,
+					u64 bp_offset,
+					struct bch_backpointer bp)
+{
+	struct bch_fs *c = trans->c;
+	struct btree *b;
+	struct bkey_s_c k;
+
+	BUG_ON(!bp.level);
+
+	bch2_trans_node_iter_init(trans, iter,
+				  bp.btree_id,
+				  bp.pos,
+				  0,
+				  bp.level - 1,
+				  0);
+	b = bch2_btree_iter_peek_node(iter);
+	if (IS_ERR(b)) {
+		bch2_trans_iter_exit(trans, iter);
+		return b;
+	}
+
+	if (extent_matches_bp(c, bp.btree_id, bp.level,
+			      bkey_i_to_s_c(&b->key),
+			      bucket, bp))
+		return b;
+
+	if (!btree_node_will_make_reachable(b))
+		backpointer_not_found(trans, bucket, bp_offset,
+				      bp, k, "btree node");
+
+	bch2_trans_iter_exit(trans, iter);
+	return NULL;
+}
+
+static int bch2_check_btree_backpointer(struct btree_trans *trans, struct btree_iter *bp_iter)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter alloc_iter = { NULL };
+	struct bch_dev *ca;
+	struct bkey_s_c k, alloc_k;
+	struct printbuf buf = PRINTBUF;
+	int ret = 0;
+
+	k = bch2_btree_iter_peek(bp_iter);
+	ret = bkey_err(k);
+	if (ret)
+		return ret;
+	if (!k.k)
+		return 0;
+
+	if (fsck_err_on(!bch2_dev_exists2(c, k.k->p.inode), c,
+			"backpointer for mising device:\n%s",
+			(bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+		ret = bch2_btree_delete_at(trans, bp_iter, 0);
+		goto out;
+	}
+
+	ca = bch_dev_bkey_exists(c, k.k->p.inode);
+
+	bch2_trans_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
+			     bp_pos_to_bucket(c, k.k->p), 0);
+
+	alloc_k = bch2_btree_iter_peek_slot(&alloc_iter);
+	ret = bkey_err(alloc_k);
+	if (ret)
+		goto out;
+
+	if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
+			"backpointer for nonexistent alloc key: %llu:%llu:0\n%s",
+			alloc_iter.pos.inode, alloc_iter.pos.offset,
+			(bch2_bkey_val_to_text(&buf, c, alloc_k), buf.buf))) {
+		ret = bch2_btree_delete_at(trans, bp_iter, 0);
+		goto out;
+	}
+out:
+fsck_err:
+	bch2_trans_iter_exit(trans, &alloc_iter);
+	printbuf_exit(&buf);
+	return ret;
+}
+
+/* verify that every backpointer has a corresponding alloc key */
+int bch2_check_btree_backpointers(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	bch2_trans_iter_init(&trans, &iter, BTREE_ID_backpointers, POS_MIN, 0);
+
+	do {
+		ret = __bch2_trans_do(&trans, NULL, NULL,
+				      BTREE_INSERT_LAZY_RW|
+				      BTREE_INSERT_NOFAIL,
+				      bch2_check_btree_backpointer(&trans, &iter));
+		if (ret)
+			break;
+	} while (bch2_btree_iter_advance(&iter));
+
+	bch2_trans_iter_exit(&trans, &iter);
+	bch2_trans_exit(&trans);
+	return ret;
+}
+
+static int check_bp_exists(struct btree_trans *trans,
+			   struct bpos bucket_pos,
+			   struct bch_backpointer bp,
+			   struct bkey_s_c orig_k)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter alloc_iter, bp_iter = { NULL };
+	struct printbuf buf = PRINTBUF;
+	struct bkey_s_c alloc_k, bp_k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &alloc_iter, BTREE_ID_alloc, bucket_pos, 0);
+	alloc_k = bch2_btree_iter_peek_slot(&alloc_iter);
+	ret = bkey_err(alloc_k);
+	if (ret)
+		goto err;
+
+	if (alloc_k.k->type == KEY_TYPE_alloc_v4) {
+		struct bkey_s_c_alloc_v4 a = bkey_s_c_to_alloc_v4(alloc_k);
+		const struct bch_backpointer *bps = alloc_v4_backpointers_c(a.v);
+		unsigned i, nr = BCH_ALLOC_V4_NR_BACKPOINTERS(a.v);
+
+		for (i = 0; i < nr; i++) {
+			int cmp = backpointer_cmp(bps[i], bp) ?:
+				memcmp(&bps[i], &bp, sizeof(bp));
+			if (!cmp)
+				goto out;
+			if (cmp >= 0)
+				break;
+		}
+	} else {
+		goto missing;
+	}
+
+	bch2_trans_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
+			     bucket_pos_to_bp(c, bucket_pos, bp.bucket_offset),
+			     0);
+	bp_k = bch2_btree_iter_peek_slot(&bp_iter);
+	ret = bkey_err(bp_k);
+	if (ret)
+		goto err;
+
+	if (bp_k.k->type != KEY_TYPE_backpointer ||
+	    memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp)))
+		goto missing;
+out:
+err:
+fsck_err:
+	bch2_trans_iter_exit(trans, &bp_iter);
+	bch2_trans_iter_exit(trans, &alloc_iter);
+	printbuf_exit(&buf);
+	return ret;
+missing:
+	prt_printf(&buf, "missing backpointer for btree=%s l=%u ",
+	       bch2_btree_ids[bp.btree_id], bp.level);
+	bch2_bkey_val_to_text(&buf, c, orig_k);
+	prt_printf(&buf, "\nin alloc key ");
+	bch2_bkey_val_to_text(&buf, c, alloc_k);
+
+	if (c->sb.version < bcachefs_metadata_version_backpointers ||
+	    fsck_err(c, "%s", buf.buf)) {
+		struct bkey_i_alloc_v4 *a = bch2_alloc_to_v4_mut(trans, alloc_k);
+
+		ret   = PTR_ERR_OR_ZERO(a) ?:
+			bch2_bucket_backpointer_add(trans, a, bp, orig_k) ?:
+			bch2_trans_update(trans, &alloc_iter, &a->k_i, 0);
+	}
+
+	goto out;
+}
+
+static int check_extent_to_backpointers(struct btree_trans *trans,
+					struct btree_iter *iter)
+{
+	struct bch_fs *c = trans->c;
+	struct bkey_ptrs_c ptrs;
+	const union bch_extent_entry *entry;
+	struct extent_ptr_decoded p;
+	struct bkey_s_c k;
+	int ret;
+
+	k = bch2_btree_iter_peek_all_levels(iter);
+	ret = bkey_err(k);
+	if (ret)
+		return ret;
+	if (!k.k)
+		return 0;
+
+	ptrs = bch2_bkey_ptrs_c(k);
+	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
+		struct bpos bucket_pos;
+		struct bch_backpointer bp;
+
+		if (p.ptr.cached)
+			continue;
+
+		bch2_extent_ptr_to_bp(c, iter->btree_id, iter->path->level,
+				      k, p, &bucket_pos, &bp);
+
+		ret = check_bp_exists(trans, bucket_pos, bp, k);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int check_btree_root_to_backpointers(struct btree_trans *trans,
+					    enum btree_id btree_id)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct btree *b;
+	struct bkey_s_c k;
+	struct bkey_ptrs_c ptrs;
+	struct extent_ptr_decoded p;
+	const union bch_extent_entry *entry;
+	int ret;
+
+	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
+				  c->btree_roots[btree_id].level, 0);
+	b = bch2_btree_iter_peek_node(&iter);
+	ret = PTR_ERR_OR_ZERO(b);
+	if (ret)
+		goto err;
+
+	BUG_ON(b != btree_node_root(c, b));
+
+	k = bkey_i_to_s_c(&b->key);
+	ptrs = bch2_bkey_ptrs_c(k);
+	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
+		struct bpos bucket_pos;
+		struct bch_backpointer bp;
+
+		if (p.ptr.cached)
+			continue;
+
+		bch2_extent_ptr_to_bp(c, iter.btree_id, iter.path->level + 1,
+				      k, p, &bucket_pos, &bp);
+
+		ret = check_bp_exists(trans, bucket_pos, bp, k);
+		if (ret)
+			goto err;
+	}
+err:
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+int bch2_check_extents_to_backpointers(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	enum btree_id btree_id;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	for (btree_id = 0; btree_id < BTREE_ID_NR; btree_id++) {
+		bch2_trans_node_iter_init(&trans, &iter, btree_id, POS_MIN, 0,
+					  0,
+					  BTREE_ITER_ALL_LEVELS|
+					  BTREE_ITER_PREFETCH);
+
+		do {
+			ret = __bch2_trans_do(&trans, NULL, NULL,
+					      BTREE_INSERT_LAZY_RW|
+					      BTREE_INSERT_NOFAIL,
+					      check_extent_to_backpointers(&trans, &iter));
+			if (ret)
+				break;
+		} while (!bch2_btree_iter_advance(&iter));
+
+		bch2_trans_iter_exit(&trans, &iter);
+
+		if (ret)
+			break;
+
+		ret = __bch2_trans_do(&trans, NULL, NULL,
+				      BTREE_INSERT_LAZY_RW|
+				      BTREE_INSERT_NOFAIL,
+				      check_btree_root_to_backpointers(&trans, btree_id));
+		if (ret)
+			break;
+	}
+	bch2_trans_exit(&trans);
+	return ret;
+}
+
+static int check_one_backpointer(struct btree_trans *trans,
+				 struct bpos bucket,
+				 u64 *bp_offset)
+{
+	struct btree_iter iter;
+	struct bch_backpointer bp;
+	struct bkey_s_c k;
+	struct printbuf buf = PRINTBUF;
+	int ret;
+
+	ret = bch2_get_next_backpointer(trans, bucket, -1,
+					bp_offset, &bp);
+	if (ret || *bp_offset == U64_MAX)
+		return ret;
+
+	k = bch2_backpointer_get_key(trans, &iter, bucket, *bp_offset, bp);
+	ret = bkey_err(k);
+	if (ret)
+		return ret;
+
+	if (fsck_err_on(!k.k, trans->c,
+			"%s backpointer points to missing extent\n%s",
+			*bp_offset < BACKPOINTER_OFFSET_MAX ? "alloc" : "btree",
+			(bch2_backpointer_to_text(&buf, &bp), buf.buf))) {
+		ret = bch2_backpointer_del_by_offset(trans, bucket, *bp_offset, bp);
+		if (ret == -ENOENT)
+			bch_err(trans->c, "backpointer at %llu not found", *bp_offset);
+	}
+
+	bch2_trans_iter_exit(trans, &iter);
+fsck_err:
+	printbuf_exit(&buf);
+	return ret;
+}
+
+int bch2_check_backpointers_to_extents(struct bch_fs *c)
+{
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret = 0;
+
+	bch2_trans_init(&trans, c, 0, 0);
+	for_each_btree_key(&trans, iter, BTREE_ID_alloc, POS_MIN,
+			   BTREE_ITER_PREFETCH, k, ret) {
+		u64 bp_offset = 0;
+
+		while (!(ret = __bch2_trans_do(&trans, NULL, NULL,
+					       BTREE_INSERT_LAZY_RW|
+					       BTREE_INSERT_NOFAIL,
+				check_one_backpointer(&trans, iter.pos, &bp_offset))) &&
+		       bp_offset < U64_MAX)
+			bp_offset++;
+
+		if (ret)
+			break;
+	}
+	bch2_trans_iter_exit(&trans, &iter);
+	bch2_trans_exit(&trans);
+	return ret < 0 ? ret : 0;
+}
diff --git a/libbcachefs/backpointers.h b/libbcachefs/backpointers.h
new file mode 100644
index 00000000..fe42af29
--- /dev/null
+++ b/libbcachefs/backpointers.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_BACKPOINTERS_BACKGROUND_H
+#define _BCACHEFS_BACKPOINTERS_BACKGROUND_H
+
+#include "super.h"
+
+int bch2_backpointer_invalid(const struct bch_fs *, struct bkey_s_c k,
+			     int, struct printbuf *);
+void bch2_backpointer_to_text(struct printbuf *, const struct bch_backpointer *);
+void bch2_backpointer_k_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);
+void bch2_backpointer_swab(struct bkey_s);
+
+#define bch2_bkey_ops_backpointer (struct bkey_ops) {	\
+	.key_invalid	= bch2_backpointer_invalid,	\
+	.val_to_text	= bch2_backpointer_k_to_text,	\
+	.swab		= bch2_backpointer_swab,	\
+}
+
+void bch2_extent_ptr_to_bp(struct bch_fs *, enum btree_id, unsigned,
+			   struct bkey_s_c, struct extent_ptr_decoded,
+			   struct bpos *, struct bch_backpointer *);
+
+int bch2_bucket_backpointer_del(struct btree_trans *, struct bkey_i_alloc_v4 *,
+				struct bch_backpointer, struct bkey_s_c);
+int bch2_bucket_backpointer_add(struct btree_trans *, struct bkey_i_alloc_v4 *,
+				struct bch_backpointer, struct bkey_s_c);
+int bch2_get_next_backpointer(struct btree_trans *, struct bpos, int,
+			      u64 *, struct bch_backpointer *);
+struct bkey_s_c bch2_backpointer_get_key(struct btree_trans *, struct btree_iter *,
+					 struct bpos, u64, struct bch_backpointer);
+struct btree *bch2_backpointer_get_node(struct btree_trans *, struct btree_iter *,
+					struct bpos, u64, struct bch_backpointer);
+
+int bch2_check_btree_backpointers(struct bch_fs *);
+int bch2_check_extents_to_backpointers(struct bch_fs *);
+int bch2_check_backpointers_to_extents(struct bch_fs *);
+
+#endif /* _BCACHEFS_BACKPOINTERS_BACKGROUND_H */
diff --git a/libbcachefs/bcachefs.h b/libbcachefs/bcachefs.h
index 2eced206..1f0484aa 100644
--- a/libbcachefs/bcachefs.h
+++ b/libbcachefs/bcachefs.h
@@ -509,6 +509,7 @@ enum {
 	BCH_FS_TOPOLOGY_REPAIR_DONE,
 	BCH_FS_INITIAL_GC_DONE,		/* kill when we enumerate fsck passes */
 	BCH_FS_CHECK_LRUS_DONE,
+	BCH_FS_CHECK_BACKPOINTERS_DONE,
 	BCH_FS_CHECK_ALLOC_TO_LRU_REFS_DONE,
 	BCH_FS_FSCK_DONE,
 	BCH_FS_INITIAL_GC_UNFIXED,	/* kill when we enumerate fsck errors */
diff --git a/libbcachefs/bcachefs_format.h b/libbcachefs/bcachefs_format.h
index dbe9a37f..147fde14 100644
--- a/libbcachefs/bcachefs_format.h
+++ b/libbcachefs/bcachefs_format.h
@@ -365,7 +365,8 @@ static inline void bkey_init(struct bkey *k)
 	x(alloc_v3,		24)			\
 	x(set,			25)			\
 	x(lru,			26)			\
-	x(alloc_v4,		27)
+	x(alloc_v4,		27)			\
+	x(backpointer,		28)
 
 enum bch_bkey_type {
 #define x(name, nr) KEY_TYPE_##name	= nr,
@@ -886,6 +887,12 @@ struct bch_alloc {
 	x(stripe,		32)		\
 	x(stripe_redundancy,	8)
 
+enum {
+#define x(name, _bits) BCH_ALLOC_FIELD_V1_##name,
+	BCH_ALLOC_FIELDS_V1()
+#undef x
+};
+
 struct bch_alloc_v2 {
 	struct bch_val		v;
 	__u8			nr_fields;
@@ -914,6 +921,9 @@ struct bch_alloc_v3 {
 	__u8			data[];
 } __attribute__((packed, aligned(8)));
 
+LE32_BITMASK(BCH_ALLOC_V3_NEED_DISCARD,struct bch_alloc_v3, flags,  0,  1)
+LE32_BITMASK(BCH_ALLOC_V3_NEED_INC_GEN,struct bch_alloc_v3, flags,  1,  2)
+
 struct bch_alloc_v4 {
 	struct bch_val		v;
 	__u64			journal_seq;
@@ -927,22 +937,27 @@ struct bch_alloc_v4 {
 	__u64			io_time[2];
 	__u32			stripe;
 	__u32			nr_external_backpointers;
-	struct bpos		backpointers[0];
 } __attribute__((packed, aligned(8)));
 
-LE32_BITMASK(BCH_ALLOC_V3_NEED_DISCARD,struct bch_alloc_v3, flags,  0,  1)
-LE32_BITMASK(BCH_ALLOC_V3_NEED_INC_GEN,struct bch_alloc_v3, flags,  1,  2)
+#define BCH_ALLOC_V4_U64s_V0	6
+#define BCH_ALLOC_V4_U64s	(sizeof(struct bch_alloc_v4) / sizeof(u64))
 
 BITMASK(BCH_ALLOC_V4_NEED_DISCARD,	struct bch_alloc_v4, flags,  0,  1)
 BITMASK(BCH_ALLOC_V4_NEED_INC_GEN,	struct bch_alloc_v4, flags,  1,  2)
 BITMASK(BCH_ALLOC_V4_BACKPOINTERS_START,struct bch_alloc_v4, flags,  2,  8)
 BITMASK(BCH_ALLOC_V4_NR_BACKPOINTERS,	struct bch_alloc_v4, flags,  8,  14)
 
-enum {
-#define x(name, _bits) BCH_ALLOC_FIELD_V1_##name,
-	BCH_ALLOC_FIELDS_V1()
-#undef x
-};
+#define BCH_ALLOC_V4_NR_BACKPOINTERS_MAX	40
+
+struct bch_backpointer {
+	struct bch_val		v;
+	__u8			btree_id;
+	__u8			level;
+	__u8			data_type;
+	__u64			bucket_offset:40;
+	__u32			bucket_len;
+	struct bpos		pos;
+} __attribute__((packed, aligned(8)));
 
 /* Quotas: */
 
@@ -1326,7 +1341,8 @@ struct bch_sb_field_disk_groups {
 	x(io_read,		0)			\
 	x(io_write,		1)			\
 	x(io_move,		2)			\
-	x(bucket_invalidate,	3)
+	x(bucket_invalidate,	3)			\
+	x(bucket_discard,	4)
 
 enum bch_persistent_counters {
 #define x(t, n, ...) BCH_COUNTER_##t,
@@ -1407,7 +1423,8 @@ struct bch_sb_field_journal_seq_blacklist {
 	x(inode_v2,			18)		\
 	x(freespace,			19)		\
 	x(alloc_v4,			20)		\
-	x(new_data_types,		21)
+	x(new_data_types,		21)		\
+	x(backpointers,			22)
 
 enum bcachefs_metadata_version {
 	bcachefs_metadata_version_min = 9,
diff --git a/libbcachefs/bkey_methods.c b/libbcachefs/bkey_methods.c
index 229d5157..fd352a67 100644
--- a/libbcachefs/bkey_methods.c
+++ b/libbcachefs/bkey_methods.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "backpointers.h"
 #include "bkey_methods.h"
 #include "btree_types.h"
 #include "alloc_background.h"
@@ -191,6 +192,9 @@ static unsigned bch2_key_types_allowed[] = {
 	[BKEY_TYPE_need_discard] =
 		(1U << KEY_TYPE_deleted)|
 		(1U << KEY_TYPE_set),
+	[BKEY_TYPE_backpointers] =
+		(1U << KEY_TYPE_deleted)|
+		(1U << KEY_TYPE_backpointer),
 	[BKEY_TYPE_btree] =
 		(1U << KEY_TYPE_deleted)|
 		(1U << KEY_TYPE_btree_ptr)|
diff --git a/libbcachefs/btree_types.h b/libbcachefs/btree_types.h
index d8f92cc9..5382f2b8 100644
--- a/libbcachefs/btree_types.h
+++ b/libbcachefs/btree_types.h
@@ -376,7 +376,7 @@ struct btree_trans_commit_hook {
 	struct btree_trans_commit_hook	*next;
 };
 
-#define BTREE_TRANS_MEM_MAX	(1U << 14)
+#define BTREE_TRANS_MEM_MAX	(1U << 16)
 
 struct btree_trans {
 	struct bch_fs		*c;
@@ -638,6 +638,11 @@ static inline bool btree_type_has_snapshots(enum btree_id id)
 	return (1 << id) & BTREE_ID_HAS_SNAPSHOTS;
 }
 
+static inline bool btree_type_has_ptrs(enum btree_id id)
+{
+	return (1 << id) & BTREE_ID_HAS_PTRS;
+}
+
 static inline bool btree_node_type_needs_gc(enum btree_node_type type)
 {
 	return BTREE_NODE_TYPE_HAS_TRIGGERS & (1U << type);
diff --git a/libbcachefs/buckets.c b/libbcachefs/buckets.c
index e2944fc4..1ea7e2ba 100644
--- a/libbcachefs/buckets.c
+++ b/libbcachefs/buckets.c
@@ -7,6 +7,7 @@
 
 #include "bcachefs.h"
 #include "alloc_background.h"
+#include "backpointers.h"
 #include "bset.h"
 #include "btree_gc.h"
 #include "btree_update.h"
@@ -655,16 +656,6 @@ err:
 	return ret;
 }
 
-static s64 ptr_disk_sectors(s64 sectors, struct extent_ptr_decoded p)
-{
-	EBUG_ON(sectors < 0);
-
-	return crc_is_compressed(p.crc)
-		? DIV_ROUND_UP_ULL(sectors * p.crc.compressed_size,
-				   p.crc.uncompressed_size)
-		: sectors;
-}
-
 static int check_bucket_ref(struct bch_fs *c,
 			    struct bkey_s_c k,
 			    const struct bch_extent_ptr *ptr,
@@ -1368,21 +1359,43 @@ need_mark:
 /* trans_mark: */
 
 static int bch2_trans_mark_pointer(struct btree_trans *trans,
-			struct bkey_s_c k, struct extent_ptr_decoded p,
-			s64 sectors, enum bch_data_type data_type)
+				   enum btree_id btree_id, unsigned level,
+				   struct bkey_s_c k, struct extent_ptr_decoded p,
+				   unsigned flags)
 {
+	bool insert = !(flags & BTREE_TRIGGER_OVERWRITE);
 	struct btree_iter iter;
 	struct bkey_i_alloc_v4 *a;
+	struct bpos bucket_pos;
+	struct bch_backpointer bp;
+	s64 sectors;
 	int ret;
 
-	a = bch2_trans_start_alloc_update(trans, &iter, PTR_BUCKET_POS(trans->c, &p.ptr));
+	bch2_extent_ptr_to_bp(trans->c, btree_id, level, k, p, &bucket_pos, &bp);
+	sectors = bp.bucket_len;
+	if (!insert)
+		sectors = -sectors;
+
+	a = bch2_trans_start_alloc_update(trans, &iter, bucket_pos);
 	if (IS_ERR(a))
 		return PTR_ERR(a);
 
-	ret = __mark_pointer(trans, k, &p.ptr, sectors, data_type,
+	ret = __mark_pointer(trans, k, &p.ptr, sectors, bp.data_type,
 			     a->v.gen, &a->v.data_type,
-			     &a->v.dirty_sectors, &a->v.cached_sectors) ?:
-		bch2_trans_update(trans, &iter, &a->k_i, 0);
+			     &a->v.dirty_sectors, &a->v.cached_sectors);
+	if (ret)
+		goto err;
+
+	if (!p.ptr.cached) {
+		ret = insert
+			? bch2_bucket_backpointer_add(trans, a, bp, k)
+			: bch2_bucket_backpointer_del(trans, a, bp, k);
+		if (ret)
+			goto err;
+	}
+
+	ret = bch2_trans_update(trans, &iter, &a->k_i, 0);
+err:
 	bch2_trans_iter_exit(trans, &iter);
 	return ret;
 }
@@ -1476,8 +1489,7 @@ int bch2_trans_mark_extent(struct btree_trans *trans,
 		if (flags & BTREE_TRIGGER_OVERWRITE)
 			disk_sectors = -disk_sectors;
 
-		ret = bch2_trans_mark_pointer(trans, k, p,
-					disk_sectors, data_type);
+		ret = bch2_trans_mark_pointer(trans, btree_id, level, k, p, flags);
 		if (ret < 0)
 			return ret;
 
diff --git a/libbcachefs/buckets.h b/libbcachefs/buckets.h
index 3469327d..670b95b8 100644
--- a/libbcachefs/buckets.h
+++ b/libbcachefs/buckets.h
@@ -75,6 +75,15 @@ static inline struct bpos PTR_BUCKET_POS(const struct bch_fs *c,
 	return POS(ptr->dev, PTR_BUCKET_NR(ca, ptr));
 }
 
+static inline struct bpos PTR_BUCKET_POS_OFFSET(const struct bch_fs *c,
+						const struct bch_extent_ptr *ptr,
+						u32 *bucket_offset)
+{
+	struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+
+	return POS(ptr->dev, sector_to_bucket_and_offset(ca, ptr->offset, bucket_offset));
+}
+
 static inline struct bucket *PTR_GC_BUCKET(struct bch_dev *ca,
 					   const struct bch_extent_ptr *ptr)
 {
@@ -90,6 +99,16 @@ static inline enum bch_data_type ptr_data_type(const struct bkey *k,
 	return ptr->cached ? BCH_DATA_cached : BCH_DATA_user;
 }
 
+static inline s64 ptr_disk_sectors(s64 sectors, struct extent_ptr_decoded p)
+{
+	EBUG_ON(sectors < 0);
+
+	return crc_is_compressed(p.crc)
+		? DIV_ROUND_UP_ULL(sectors * p.crc.compressed_size,
+				   p.crc.uncompressed_size)
+		: sectors;
+}
+
 static inline int gen_cmp(u8 a, u8 b)
 {
 	return (s8) (a - b);
@@ -144,12 +163,25 @@ static inline u64 bch2_dev_buckets_reserved(struct bch_dev *ca, enum alloc_reser
 	return reserved;
 }
 
+static inline u64 dev_buckets_free(struct bch_dev *ca,
+				   struct bch_dev_usage usage,
+				   enum alloc_reserve reserve)
+{
+	return max_t(s64, 0,
+		     usage.d[BCH_DATA_free].buckets -
+		     ca->nr_open_buckets -
+		     bch2_dev_buckets_reserved(ca, reserve));
+}
+
 static inline u64 __dev_buckets_available(struct bch_dev *ca,
 					  struct bch_dev_usage usage,
 					  enum alloc_reserve reserve)
 {
 	return max_t(s64, 0,
 		     usage.d[BCH_DATA_free].buckets -
+		     usage.d[BCH_DATA_cached].buckets -
+		     usage.d[BCH_DATA_need_gc_gens].buckets -
+		     usage.d[BCH_DATA_need_discard].buckets -
 		     ca->nr_open_buckets -
 		     bch2_dev_buckets_reserved(ca, reserve));
 }
diff --git a/libbcachefs/buckets_types.h b/libbcachefs/buckets_types.h
index 0a9dd5af..1dbba7d9 100644
--- a/libbcachefs/buckets_types.h
+++ b/libbcachefs/buckets_types.h
@@ -95,7 +95,7 @@ struct copygc_heap_entry {
 	u8			replicas;
 	u32			fragmentation;
 	u32			sectors;
-	u64			offset;
+	u64			bucket;
 };
 
 typedef HEAP(struct copygc_heap_entry) copygc_heap;
diff --git a/libbcachefs/fsck.c b/libbcachefs/fsck.c
index f1abec95..81bfd6ea 100644
--- a/libbcachefs/fsck.c
+++ b/libbcachefs/fsck.c
@@ -1015,47 +1015,6 @@ static int check_subvols(struct bch_fs *c)
 	return ret;
 }
 
-/*
- * Checking for overlapping extents needs to be reimplemented
- */
-#if 0
-static int fix_overlapping_extent(struct btree_trans *trans,
-				       struct bkey_s_c k, struct bpos cut_at)
-{
-	struct btree_iter iter;
-	struct bkey_i *u;
-	int ret;
-
-	u = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
-	ret = PTR_ERR_OR_ZERO(u);
-	if (ret)
-		return ret;
-
-	bkey_reassemble(u, k);
-	bch2_cut_front(cut_at, u);
-
-
-	/*
-	 * We don't want to go through the extent_handle_overwrites path:
-	 *
-	 * XXX: this is going to screw up disk accounting, extent triggers
-	 * assume things about extent overwrites - we should be running the
-	 * triggers manually here
-	 */
-	bch2_trans_iter_init(trans, &iter, BTREE_ID_extents, u->k.p,
-			     BTREE_ITER_INTENT|BTREE_ITER_NOT_EXTENTS);
-
-	BUG_ON(iter.flags & BTREE_ITER_IS_EXTENTS);
-	ret   = bch2_btree_iter_traverse(&iter) ?:
-		bch2_trans_update(trans, &iter, u, BTREE_TRIGGER_NORUN) ?:
-		bch2_trans_commit(trans, NULL, NULL,
-				  BTREE_INSERT_NOFAIL|
-				  BTREE_INSERT_LAZY_RW);
-	bch2_trans_iter_exit(trans, &iter);
-	return ret;
-}
-#endif
-
 static struct bkey_s_c_dirent dirent_get_by_pos(struct btree_trans *trans,
 						struct btree_iter *iter,
 						struct bpos pos)
@@ -1150,9 +1109,72 @@ fsck_err:
 	return ret ?: ret2;
 }
 
+struct extent_end {
+	u32		snapshot;
+	u64		offset;
+};
+
+typedef DARRAY(struct extent_end) extent_ends;
+
+static int extent_ends_at(extent_ends *extent_ends,
+			  struct bkey_s_c k)
+{
+	struct extent_end *i, n = (struct extent_end) {
+		.snapshot	= k.k->p.snapshot,
+		.offset		= k.k->p.offset,
+	};
+
+	darray_for_each(*extent_ends, i) {
+		if (i->snapshot == k.k->p.snapshot) {
+			*i = n;
+			return 0;
+		}
+
+		if (i->snapshot >= k.k->p.snapshot)
+			break;
+	}
+
+	return darray_insert_item(extent_ends, i - extent_ends->data, n);
+}
+
+static int check_extent_start(struct btree_trans *trans,
+			      struct snapshots_seen *s,
+			      extent_ends *extent_ends,
+			      struct bkey_s_c k,
+			      struct btree_iter *iter)
+{
+	struct bch_fs *c = trans->c;
+	struct extent_end *i;
+	struct printbuf buf = PRINTBUF;
+	int ret = 0;
+
+	darray_for_each(*extent_ends, i) {
+		if (fsck_err_on(i->offset > bkey_start_offset(k.k) &&
+				key_visible_in_snapshot(c, s, i->snapshot, k.k->p.snapshot), c,
+				"overlapping extents: extent in snapshot %u ends at %llu overlaps with\n%s",
+				i->snapshot,
+				i->offset,
+				(printbuf_reset(&buf),
+				 bch2_bkey_val_to_text(&buf, c, k), buf.buf))) {
+			struct bkey_i *update = bch2_trans_kmalloc(trans, bkey_bytes(k.k));
+			if ((ret = PTR_ERR_OR_ZERO(update)))
+				goto err;
+			bkey_reassemble(update, k);
+			ret = bch2_trans_update_extent(trans, iter, update, 0);
+			if (!ret)
+				goto err;
+		}
+	}
+err:
+fsck_err:
+	printbuf_exit(&buf);
+	return ret;
+}
+
 static int check_extent(struct btree_trans *trans, struct btree_iter *iter,
 			struct inode_walker *inode,
-			struct snapshots_seen *s)
+			struct snapshots_seen *s,
+			extent_ends *extent_ends)
 {
 	struct bch_fs *c = trans->c;
 	struct bkey_s_c k;
@@ -1182,6 +1204,8 @@ peek:
 		goto out;
 
 	if (inode->cur_inum != k.k->p.inode) {
+		extent_ends->nr = 0;
+
 		ret = check_i_sectors(trans, inode);
 		if (ret)
 			goto err;
@@ -1195,20 +1219,7 @@ peek:
 		 */
 		goto peek;
 	}
-#if 0
-	if (bkey_cmp(prev.k->k.p, bkey_start_pos(k.k)) > 0) {
-		char buf1[200];
-		char buf2[200];
 
-		bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(prev.k));
-		bch2_bkey_val_to_text(&PBUF(buf2), c, k);
-
-		if (fsck_err(c, "overlapping extents:\n%s\n%s", buf1, buf2)) {
-			ret = fix_overlapping_extent(trans, k, prev.k->k.p) ?: -EINTR;
-			goto out;
-		}
-	}
-#endif
 	ret = __walk_inode(trans, inode, k.k->p);
 	if (ret < 0)
 		goto err;
@@ -1259,13 +1270,17 @@ peek:
 		}
 	}
 
+	ret = check_extent_start(trans, s, extent_ends, k, iter);
+	if (ret)
+		goto err;
+
 	if (bkey_extent_is_allocation(k.k))
 		for_each_visible_inode(c, s, inode, k.k->p.snapshot, i)
 			i->count += k.k->size;
-#if 0
-	bch2_bkey_buf_reassemble(&prev, c, k);
-#endif
 
+	ret = extent_ends_at(extent_ends, k);
+	if (ret)
+		goto err;
 out:
 err:
 fsck_err:
@@ -1287,13 +1302,9 @@ static int check_extents(struct bch_fs *c)
 	struct snapshots_seen s;
 	struct btree_trans trans;
 	struct btree_iter iter;
+	extent_ends extent_ends = { 0 };
 	int ret = 0;
 
-#if 0
-	struct bkey_buf prev;
-	bch2_bkey_buf_init(&prev);
-	prev.k->k = KEY(0, 0, 0);
-#endif
 	snapshots_seen_init(&s);
 	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 0);
 
@@ -1309,14 +1320,12 @@ static int check_extents(struct bch_fs *c)
 		ret = __bch2_trans_do(&trans, NULL, NULL,
 				      BTREE_INSERT_LAZY_RW|
 				      BTREE_INSERT_NOFAIL,
-			check_extent(&trans, &iter, &w, &s));
+			check_extent(&trans, &iter, &w, &s, &extent_ends));
 		if (ret)
 			break;
 	} while (bch2_btree_iter_advance(&iter));
 	bch2_trans_iter_exit(&trans, &iter);
-#if 0
-	bch2_bkey_buf_exit(&prev, c);
-#endif
+	darray_exit(&extent_ends);
 	inode_walker_exit(&w);
 	bch2_trans_exit(&trans);
 	snapshots_seen_exit(&s);
diff --git a/libbcachefs/move.c b/libbcachefs/move.c
index a8f6d5a3..36d20dc8 100644
--- a/libbcachefs/move.c
+++ b/libbcachefs/move.c
@@ -1,7 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "alloc_background.h"
 #include "alloc_foreground.h"
+#include "backpointers.h"
 #include "bkey_buf.h"
 #include "btree_gc.h"
 #include "btree_update.h"
@@ -9,6 +11,7 @@
 #include "buckets.h"
 #include "disk_groups.h"
 #include "ec.h"
+#include "error.h"
 #include "inode.h"
 #include "io.h"
 #include "journal_reclaim.h"
@@ -632,6 +635,70 @@ err:
 	return ret;
 }
 
+static int move_ratelimit(struct btree_trans *trans,
+			  struct moving_context *ctxt,
+			  struct bch_ratelimit *rate)
+{
+	u64 delay;
+
+	do {
+		delay = rate ? bch2_ratelimit_delay(rate) : 0;
+
+		if (delay) {
+			bch2_trans_unlock(trans);
+			set_current_state(TASK_INTERRUPTIBLE);
+		}
+
+		if ((current->flags & PF_KTHREAD) && kthread_should_stop()) {
+			__set_current_state(TASK_RUNNING);
+			return 1;
+		}
+
+		if (delay)
+			schedule_timeout(delay);
+
+		if (unlikely(freezing(current))) {
+			move_ctxt_wait_event(ctxt, trans, list_empty(&ctxt->reads));
+			try_to_freeze();
+		}
+	} while (delay);
+
+	move_ctxt_wait_event(ctxt, trans,
+		atomic_read(&ctxt->write_sectors) <
+		SECTORS_IN_FLIGHT_PER_DEVICE);
+
+	move_ctxt_wait_event(ctxt, trans,
+		atomic_read(&ctxt->read_sectors) <
+		SECTORS_IN_FLIGHT_PER_DEVICE);
+
+	return 0;
+}
+
+static int move_get_io_opts(struct btree_trans *trans,
+			    struct bch_io_opts *io_opts,
+			    struct bkey_s_c k, u64 *cur_inum)
+{
+	struct bch_inode_unpacked inode;
+	int ret;
+
+	if (*cur_inum == k.k->p.inode)
+		return 0;
+
+	*io_opts = bch2_opts_to_inode_opts(trans->c->opts);
+
+	ret = lookup_inode(trans,
+			   SPOS(0, k.k->p.inode, k.k->p.snapshot),
+			   &inode);
+	if (ret == -EINTR)
+		return ret;
+
+	if (!ret)
+		bch2_io_opts_apply(io_opts, bch2_inode_opts_get(&inode));
+
+	*cur_inum = k.k->p.inode;
+	return 0;
+}
+
 static int __bch2_move_data(struct bch_fs *c,
 		struct moving_context *ctxt,
 		struct bch_ratelimit *rate,
@@ -642,7 +709,6 @@ static int __bch2_move_data(struct bch_fs *c,
 		struct bch_move_stats *stats,
 		enum btree_id btree_id)
 {
-	bool kthread = (current->flags & PF_KTHREAD) != 0;
 	struct bch_io_opts io_opts = bch2_opts_to_inode_opts(c->opts);
 	struct bkey_buf sk;
 	struct btree_trans trans;
@@ -650,7 +716,7 @@ static int __bch2_move_data(struct bch_fs *c,
 	struct bkey_s_c k;
 	struct data_opts data_opts;
 	enum data_cmd data_cmd;
-	u64 delay, cur_inum = U64_MAX;
+	u64 cur_inum = U64_MAX;
 	int ret = 0, ret2;
 
 	bch2_bkey_buf_init(&sk);
@@ -667,37 +733,7 @@ static int __bch2_move_data(struct bch_fs *c,
 	if (rate)
 		bch2_ratelimit_reset(rate);
 
-	while (1) {
-		do {
-			delay = rate ? bch2_ratelimit_delay(rate) : 0;
-
-			if (delay) {
-				bch2_trans_unlock(&trans);
-				set_current_state(TASK_INTERRUPTIBLE);
-			}
-
-			if (kthread && (ret = kthread_should_stop())) {
-				__set_current_state(TASK_RUNNING);
-				goto out;
-			}
-
-			if (delay)
-				schedule_timeout(delay);
-
-			if (unlikely(freezing(current))) {
-				move_ctxt_wait_event(ctxt, &trans, list_empty(&ctxt->reads));
-				try_to_freeze();
-			}
-		} while (delay);
-
-		move_ctxt_wait_event(ctxt, &trans,
-			atomic_read(&ctxt->write_sectors) <
-			SECTORS_IN_FLIGHT_PER_DEVICE);
-
-		move_ctxt_wait_event(ctxt, &trans,
-			atomic_read(&ctxt->read_sectors) <
-			SECTORS_IN_FLIGHT_PER_DEVICE);
-
+	while (!move_ratelimit(&trans, ctxt, rate)) {
 		bch2_trans_begin(&trans);
 
 		k = bch2_btree_iter_peek(&iter);
@@ -718,23 +754,9 @@ static int __bch2_move_data(struct bch_fs *c,
 		if (!bkey_extent_is_direct_data(k.k))
 			goto next_nondata;
 
-		if (btree_id == BTREE_ID_extents &&
-		    cur_inum != k.k->p.inode) {
-			struct bch_inode_unpacked inode;
-
-			io_opts = bch2_opts_to_inode_opts(c->opts);
-
-			ret = lookup_inode(&trans,
-					SPOS(0, k.k->p.inode, k.k->p.snapshot),
-					&inode);
-			if (ret == -EINTR)
-				continue;
-
-			if (!ret)
-				bch2_io_opts_apply(&io_opts, bch2_inode_opts_get(&inode));
-
-			cur_inum = k.k->p.inode;
-		}
+		ret = move_get_io_opts(&trans, &io_opts, k, &cur_inum);
+		if (ret)
+			continue;
 
 		switch ((data_cmd = pred(c, arg, k, &io_opts, &data_opts))) {
 		case DATA_SKIP:
@@ -779,7 +801,6 @@ next:
 next_nondata:
 		bch2_btree_iter_advance(&iter);
 	}
-out:
 
 	bch2_trans_iter_exit(&trans, &iter);
 	bch2_trans_exit(&trans);
@@ -848,7 +869,6 @@ int bch2_move_data(struct bch_fs *c,
 			break;
 	}
 
-
 	move_ctxt_wait_event(&ctxt, NULL, list_empty(&ctxt.reads));
 	closure_sync(&ctxt.cl);
 
@@ -862,6 +882,167 @@ int bch2_move_data(struct bch_fs *c,
 	return ret;
 }
 
+static int verify_bucket_evacuated(struct btree_trans *trans, struct bpos bucket, int gen)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_iter iter;
+	struct bkey_s_c k;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, BTREE_ID_alloc,
+			     bucket, BTREE_ITER_CACHED);
+	k = bch2_btree_iter_peek_slot(&iter);
+	ret = bkey_err(k);
+
+	if (!ret && k.k->type == KEY_TYPE_alloc_v4) {
+		struct bkey_s_c_alloc_v4 a = bkey_s_c_to_alloc_v4(k);
+
+		if (a.v->gen == gen &&
+		    a.v->dirty_sectors) {
+			struct printbuf buf = PRINTBUF;
+
+			prt_str(&buf, "failed to evacuate bucket ");
+			bch2_bkey_val_to_text(&buf, c, k);
+
+			bch_err_ratelimited(c, "%s", buf.buf);
+			printbuf_exit(&buf);
+		}
+	}
+
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+int bch2_evacuate_bucket(struct bch_fs *c,
+			 struct bpos bucket, int gen,
+			 struct bch_ratelimit *rate,
+			 struct write_point_specifier wp,
+			 enum data_cmd data_cmd,
+			 struct data_opts *data_opts,
+			 struct bch_move_stats *stats)
+{
+	struct bch_io_opts io_opts = bch2_opts_to_inode_opts(c->opts);
+	struct moving_context ctxt = { .stats = stats };
+	struct btree_trans trans;
+	struct btree_iter iter;
+	struct bkey_buf sk;
+	struct bch_backpointer bp;
+	u64 bp_offset = 0, cur_inum = U64_MAX;
+	int ret = 0;
+
+	bch2_bkey_buf_init(&sk);
+	bch2_trans_init(&trans, c, 0, 0);
+	progress_list_add(c, stats);
+	closure_init_stack(&ctxt.cl);
+	INIT_LIST_HEAD(&ctxt.reads);
+	init_waitqueue_head(&ctxt.wait);
+
+	stats->data_type = BCH_DATA_user;
+
+	while (!(ret = move_ratelimit(&trans, &ctxt, rate))) {
+		bch2_trans_begin(&trans);
+
+		ret = bch2_get_next_backpointer(&trans, bucket, gen,
+						&bp_offset, &bp);
+		if (ret == -EINTR)
+			continue;
+		if (ret)
+			goto err;
+		if (bp_offset == U64_MAX)
+			break;
+
+		if (!bp.level) {
+			struct bkey_s_c k;
+
+			k = bch2_backpointer_get_key(&trans, &iter,
+						bucket, bp_offset, bp);
+			ret = bkey_err(k);
+			if (ret == -EINTR)
+				continue;
+			if (ret)
+				goto err;
+			if (!k.k)
+				continue;
+
+			bch2_bkey_buf_reassemble(&sk, c, k);
+			k = bkey_i_to_s_c(sk.k);
+			bch2_trans_iter_exit(&trans, &iter);
+
+			ret = move_get_io_opts(&trans, &io_opts, k, &cur_inum);
+			if (ret)
+				continue;
+
+			data_opts->target	= io_opts.background_target;
+			data_opts->rewrite_dev	= bucket.inode;
+
+			ret = bch2_move_extent(&trans, &ctxt, wp, io_opts, bp.btree_id, k,
+						data_cmd, *data_opts);
+			if (ret == -EINTR)
+				continue;
+			if (ret == -ENOMEM) {
+				/* memory allocation failure, wait for some IO to finish */
+				bch2_move_ctxt_wait_for_io(&ctxt, &trans);
+				continue;
+			}
+			if (ret)
+				goto err;
+
+			if (rate)
+				bch2_ratelimit_increment(rate, k.k->size);
+			atomic64_add(k.k->size, &stats->sectors_seen);
+		} else {
+			struct btree *b;
+
+			b = bch2_backpointer_get_node(&trans, &iter,
+						bucket, bp_offset, bp);
+			ret = PTR_ERR_OR_ZERO(b);
+			if (ret == -EINTR)
+				continue;
+			if (ret)
+				goto err;
+			if (!b)
+				continue;
+
+			ret = bch2_btree_node_rewrite(&trans, &iter, b, 0);
+			bch2_trans_iter_exit(&trans, &iter);
+
+			if (ret == -EINTR)
+				continue;
+			if (ret)
+				goto err;
+
+			if (rate)
+				bch2_ratelimit_increment(rate, c->opts.btree_node_size >> 9);
+			atomic64_add(c->opts.btree_node_size >> 9, &stats->sectors_seen);
+			atomic64_add(c->opts.btree_node_size >> 9, &stats->sectors_moved);
+		}
+
+		bp_offset++;
+	}
+
+	if (IS_ENABLED(CONFIG_BCACHEFS_DEBUG) && gen >= 0) {
+		bch2_trans_unlock(&trans);
+		move_ctxt_wait_event(&ctxt, NULL, list_empty(&ctxt.reads));
+		closure_sync(&ctxt.cl);
+		lockrestart_do(&trans, verify_bucket_evacuated(&trans, bucket, gen));
+	}
+err:
+	bch2_trans_exit(&trans);
+	bch2_bkey_buf_exit(&sk, c);
+
+	move_ctxt_wait_event(&ctxt, NULL, list_empty(&ctxt.reads));
+	closure_sync(&ctxt.cl);
+	progress_list_del(c, stats);
+
+	EBUG_ON(atomic_read(&ctxt.write_sectors));
+
+	trace_move_data(c,
+			atomic64_read(&stats->sectors_moved),
+			atomic64_read(&stats->keys_moved));
+
+	return ret;
+}
+
 typedef enum data_cmd (*move_btree_pred)(struct bch_fs *, void *,
 					 struct btree *, struct bch_io_opts *,
 					 struct data_opts *);
diff --git a/libbcachefs/move.h b/libbcachefs/move.h
index 2a789a11..c69b6b5a 100644
--- a/libbcachefs/move.h
+++ b/libbcachefs/move.h
@@ -62,6 +62,12 @@ int bch2_move_data(struct bch_fs *,
 		   move_pred_fn, void *,
 		   struct bch_move_stats *);
 
+int bch2_evacuate_bucket(struct bch_fs *, struct bpos, int,
+			 struct bch_ratelimit *,
+			 struct write_point_specifier,
+			 enum data_cmd,
+			 struct data_opts *,
+			 struct bch_move_stats *);
 int bch2_data_job(struct bch_fs *,
 		  struct bch_move_stats *,
 		  struct bch_ioctl_data);
diff --git a/libbcachefs/movinggc.c b/libbcachefs/movinggc.c
index 99980c3d..efb09e1c 100644
--- a/libbcachefs/movinggc.c
+++ b/libbcachefs/movinggc.c
@@ -30,80 +30,6 @@
 #include <linux/sort.h>
 #include <linux/wait.h>
 
-static int bucket_offset_cmp(const void *_l, const void *_r, size_t size)
-{
-	const struct copygc_heap_entry *l = _l;
-	const struct copygc_heap_entry *r = _r;
-
-	return  cmp_int(l->dev,    r->dev) ?:
-		cmp_int(l->offset, r->offset);
-}
-
-static enum data_cmd copygc_pred(struct bch_fs *c, void *arg,
-				 struct bkey_s_c k,
-				 struct bch_io_opts *io_opts,
-				 struct data_opts *data_opts)
-{
-	copygc_heap *h = &c->copygc_heap;
-	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
-	const union bch_extent_entry *entry;
-	struct extent_ptr_decoded p = { 0 };
-
-	bkey_for_each_ptr_decode(k.k, ptrs, p, entry) {
-		struct bch_dev *ca = bch_dev_bkey_exists(c, p.ptr.dev);
-		struct copygc_heap_entry search = {
-			.dev	= p.ptr.dev,
-			.offset	= p.ptr.offset,
-		};
-		ssize_t i;
-
-		if (p.ptr.cached)
-			continue;
-
-		i = eytzinger0_find_le(h->data, h->used,
-				       sizeof(h->data[0]),
-				       bucket_offset_cmp, &search);
-#if 0
-		/* eytzinger search verify code: */
-		ssize_t j = -1, k;
-
-		for (k = 0; k < h->used; k++)
-			if (h->data[k].offset <= ptr->offset &&
-			    (j < 0 || h->data[k].offset > h->data[j].offset))
-				j = k;
-
-		BUG_ON(i != j);
-#endif
-		if (i >= 0 &&
-		    p.ptr.dev == h->data[i].dev &&
-		    p.ptr.offset < h->data[i].offset + ca->mi.bucket_size &&
-		    p.ptr.gen == h->data[i].gen) {
-			/*
-			 * We need to use the journal reserve here, because
-			 *  - journal reclaim depends on btree key cache
-			 *    flushing to make forward progress,
-			 *  - which has to make forward progress when the
-			 *    journal is pre-reservation full,
-			 *  - and depends on allocation - meaning allocator and
-			 *    copygc
-			 */
-
-			data_opts->target		= io_opts->background_target;
-			data_opts->nr_replicas		= 1;
-			data_opts->btree_insert_flags	= BTREE_INSERT_USE_RESERVE|
-				JOURNAL_WATERMARK_copygc;
-			data_opts->rewrite_dev		= p.ptr.dev;
-
-			if (p.has_ec)
-				data_opts->nr_replicas += p.ec.redundancy;
-
-			return DATA_REWRITE;
-		}
-	}
-
-	return DATA_SKIP;
-}
-
 static inline int fragmentation_cmp(copygc_heap *heap,
 				   struct copygc_heap_entry l,
 				   struct copygc_heap_entry r)
@@ -111,7 +37,7 @@ static inline int fragmentation_cmp(copygc_heap *heap,
 	return cmp_int(l.fragmentation, r.fragmentation);
 }
 
-static int walk_buckets_to_copygc(struct bch_fs *c)
+static int find_buckets_to_copygc(struct bch_fs *c)
 {
 	copygc_heap *h = &c->copygc_heap;
 	struct btree_trans trans;
@@ -122,6 +48,14 @@ static int walk_buckets_to_copygc(struct bch_fs *c)
 
 	bch2_trans_init(&trans, c, 0, 0);
 
+	/*
+	 * Find buckets with lowest sector counts, skipping completely
+	 * empty buckets, by building a maxheap sorted by sector count,
+	 * and repeatedly replacing the maximum element until all
+	 * buckets have been visited.
+	 */
+	h->used = 0;
+
 	for_each_btree_key(&trans, iter, BTREE_ID_alloc, POS_MIN,
 			   BTREE_ITER_PREFETCH, k, ret) {
 		struct bch_dev *ca = bch_dev_bkey_exists(c, iter.pos.inode);
@@ -129,7 +63,8 @@ static int walk_buckets_to_copygc(struct bch_fs *c)
 
 		bch2_alloc_to_v4(k, &a);
 
-		if (a.data_type != BCH_DATA_user ||
+		if ((a.data_type != BCH_DATA_btree &&
+		     a.data_type != BCH_DATA_user) ||
 		    a.dirty_sectors >= ca->mi.bucket_size ||
 		    bch2_bucket_is_open(c, iter.pos.inode, iter.pos.offset))
 			continue;
@@ -141,7 +76,7 @@ static int walk_buckets_to_copygc(struct bch_fs *c)
 			.fragmentation	= div_u64((u64) a.dirty_sectors * (1ULL << 31),
 						  ca->mi.bucket_size),
 			.sectors	= a.dirty_sectors,
-			.offset		= bucket_to_sector(ca, iter.pos.offset),
+			.bucket		= iter.pos.offset,
 		};
 		heap_add_or_replace(h, e, -fragmentation_cmp, NULL);
 
@@ -152,77 +87,22 @@ static int walk_buckets_to_copygc(struct bch_fs *c)
 	return ret;
 }
 
-static int bucket_inorder_cmp(const void *_l, const void *_r)
-{
-	const struct copygc_heap_entry *l = _l;
-	const struct copygc_heap_entry *r = _r;
-
-	return cmp_int(l->dev, r->dev) ?: cmp_int(l->offset, r->offset);
-}
-
-static int check_copygc_was_done(struct bch_fs *c,
-				 u64 *sectors_not_moved,
-				 u64 *buckets_not_moved)
-{
-	copygc_heap *h = &c->copygc_heap;
-	struct btree_trans trans;
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	struct bch_alloc_v4 a;
-	struct copygc_heap_entry *i;
-	int ret = 0;
-
-	sort(h->data, h->used, sizeof(h->data[0]), bucket_inorder_cmp, NULL);
-
-	bch2_trans_init(&trans, c, 0, 0);
-	bch2_trans_iter_init(&trans, &iter, BTREE_ID_alloc, POS_MIN, 0);
-
-	for (i = h->data; i < h->data + h->used; i++) {
-		struct bch_dev *ca = bch_dev_bkey_exists(c, i->dev);
-
-		bch2_btree_iter_set_pos(&iter, POS(i->dev, sector_to_bucket(ca, i->offset)));
-
-		ret = lockrestart_do(&trans,
-				bkey_err(k = bch2_btree_iter_peek_slot(&iter)));
-		if (ret)
-			break;
-
-		bch2_alloc_to_v4(k, &a);
-
-		if (a.gen == i->gen && a.dirty_sectors) {
-			*sectors_not_moved += a.dirty_sectors;
-			*buckets_not_moved += 1;
-		}
-	}
-	bch2_trans_iter_exit(&trans, &iter);
-
-	bch2_trans_exit(&trans);
-	return ret;
-}
-
 static int bch2_copygc(struct bch_fs *c)
 {
 	copygc_heap *h = &c->copygc_heap;
-	struct copygc_heap_entry e, *i;
+	struct copygc_heap_entry e;
 	struct bch_move_stats move_stats;
-	u64 sectors_to_move = 0, sectors_to_write = 0, sectors_not_moved = 0;
-	u64 sectors_reserved = 0;
-	u64 buckets_to_move, buckets_not_moved = 0;
 	struct bch_dev *ca;
 	unsigned dev_idx;
 	size_t heap_size = 0;
+	struct data_opts data_opts = {
+		.nr_replicas		= 1,
+		.btree_insert_flags	= BTREE_INSERT_USE_RESERVE|JOURNAL_WATERMARK_copygc,
+	};
 	int ret;
 
 	bch_move_stats_init(&move_stats, "copygc");
 
-	/*
-	 * Find buckets with lowest sector counts, skipping completely
-	 * empty buckets, by building a maxheap sorted by sector count,
-	 * and repeatedly replacing the maximum element until all
-	 * buckets have been visited.
-	 */
-	h->used = 0;
-
 	for_each_rw_member(ca, c, dev_idx)
 		heap_size += ca->mi.nbuckets >> 7;
 
@@ -234,21 +114,7 @@ static int bch2_copygc(struct bch_fs *c)
 		}
 	}
 
-	for_each_rw_member(ca, c, dev_idx) {
-		struct bch_dev_usage usage = bch2_dev_usage_read(ca);
-
-		u64 avail = max_t(s64, 0,
-				  usage.d[BCH_DATA_free].buckets +
-				  usage.d[BCH_DATA_need_discard].buckets -
-				  ca->nr_open_buckets -
-				  bch2_dev_buckets_reserved(ca, RESERVE_movinggc));
-
-		avail = min(avail, ca->mi.nbuckets >> 6);
-
-		sectors_reserved += avail * ca->mi.bucket_size;
-	}
-
-	ret = walk_buckets_to_copygc(c);
+	ret = find_buckets_to_copygc(c);
 	if (ret) {
 		bch2_fs_fatal_error(c, "error walking buckets to copygc!");
 		return ret;
@@ -259,68 +125,24 @@ static int bch2_copygc(struct bch_fs *c)
 		return 0;
 	}
 
-	/*
-	 * Our btree node allocations also come out of RESERVE_movingc:
-	 */
-	sectors_reserved = (sectors_reserved * 3) / 4;
-	if (!sectors_reserved) {
-		bch2_fs_fatal_error(c, "stuck, ran out of copygc reserve!");
-		return -1;
-	}
+	heap_resort(h, fragmentation_cmp, NULL);
 
-	for (i = h->data; i < h->data + h->used; i++) {
-		sectors_to_move += i->sectors;
-		sectors_to_write += i->sectors * i->replicas;
-	}
-
-	while (sectors_to_write > sectors_reserved) {
+	while (h->used) {
 		BUG_ON(!heap_pop(h, e, -fragmentation_cmp, NULL));
-		sectors_to_write -= e.sectors * e.replicas;
+		/* not correct w.r.t. device removal */
+
+		ret = bch2_evacuate_bucket(c, POS(e.dev, e.bucket), e.gen, NULL,
+					   writepoint_ptr(&c->copygc_write_point),
+					   DATA_REWRITE, &data_opts,
+					   &move_stats);
+		if (ret < 0)
+			bch_err(c, "error %i from bch2_move_data() in copygc", ret);
+		if (ret)
+			return ret;
 	}
 
-	buckets_to_move = h->used;
-
-	if (!buckets_to_move) {
-		bch_err_ratelimited(c, "copygc cannot run - sectors_reserved %llu!",
-				    sectors_reserved);
-		return 0;
-	}
-
-	eytzinger0_sort(h->data, h->used,
-			sizeof(h->data[0]),
-			bucket_offset_cmp, NULL);
-
-	ret = bch2_move_data(c,
-			     0,			POS_MIN,
-			     BTREE_ID_NR,	POS_MAX,
-			     NULL,
-			     writepoint_ptr(&c->copygc_write_point),
-			     copygc_pred, NULL,
-			     &move_stats);
-	if (ret < 0)
-		bch_err(c, "error %i from bch2_move_data() in copygc", ret);
-	if (ret)
-		return ret;
-
-	ret = check_copygc_was_done(c, &sectors_not_moved, &buckets_not_moved);
-	if (ret) {
-		bch_err(c, "error %i from check_copygc_was_done()", ret);
-		return ret;
-	}
-
-	if (sectors_not_moved)
-		bch_warn_ratelimited(c,
-			"copygc finished but %llu/%llu sectors, %llu/%llu buckets not moved (move stats: moved %llu sectors, raced %llu keys, %llu sectors)",
-			 sectors_not_moved, sectors_to_move,
-			 buckets_not_moved, buckets_to_move,
-			 atomic64_read(&move_stats.sectors_moved),
-			 atomic64_read(&move_stats.keys_raced),
-			 atomic64_read(&move_stats.sectors_raced));
-
-	trace_copygc(c,
-		     atomic64_read(&move_stats.sectors_moved), sectors_not_moved,
-		     buckets_to_move, buckets_not_moved);
-	return 0;
+	trace_copygc(c, atomic64_read(&move_stats.sectors_moved), 0, 0, 0);
+	return ret;
 }
 
 /*
diff --git a/libbcachefs/recovery.c b/libbcachefs/recovery.c
index 480abf13..63e8c1c3 100644
--- a/libbcachefs/recovery.c
+++ b/libbcachefs/recovery.c
@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "backpointers.h"
 #include "bkey_buf.h"
 #include "alloc_background.h"
 #include "btree_gc.h"
@@ -1075,8 +1076,8 @@ int bch2_fs_recovery(struct bch_fs *c)
 	}
 
 	if (!c->opts.nochanges) {
-		if (c->sb.version < bcachefs_metadata_version_new_data_types) {
-			bch_info(c, "version prior to new_data_types, upgrade and fsck required");
+		if (c->sb.version < bcachefs_metadata_version_backpointers) {
+			bch_info(c, "version prior to backpointers, upgrade and fsck required");
 			c->opts.version_upgrade	= true;
 			c->opts.fsck		= true;
 			c->opts.fix_errors	= FSCK_OPT_YES;
@@ -1254,6 +1255,28 @@ use_clean:
 		bch_verbose(c, "done checking lrus");
 		set_bit(BCH_FS_CHECK_LRUS_DONE, &c->flags);
 
+		bch_info(c, "checking backpointers to alloc keys");
+		err = "error checking backpointers to alloc keys";
+		ret = bch2_check_btree_backpointers(c);
+		if (ret)
+			goto err;
+		bch_verbose(c, "done checking backpointers to alloc keys");
+
+		bch_info(c, "checking backpointers to extents");
+		err = "error checking backpointers to extents";
+		ret = bch2_check_backpointers_to_extents(c);
+		if (ret)
+			goto err;
+		bch_verbose(c, "done checking backpointers to extents");
+
+		bch_info(c, "checking extents to backpointers");
+		err = "error checking extents to backpointers";
+		ret = bch2_check_extents_to_backpointers(c);
+		if (ret)
+			goto err;
+		bch_verbose(c, "done checking extents to backpointers");
+		set_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags);
+
 		bch_info(c, "checking alloc to lru refs");
 		err = "error checking alloc to lru refs";
 		ret = bch2_check_alloc_to_lru_refs(c);
@@ -1265,6 +1288,7 @@ use_clean:
 		set_bit(BCH_FS_MAY_GO_RW, &c->flags);
 		set_bit(BCH_FS_INITIAL_GC_DONE, &c->flags);
 		set_bit(BCH_FS_CHECK_LRUS_DONE, &c->flags);
+		set_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags);
 		set_bit(BCH_FS_CHECK_ALLOC_TO_LRU_REFS_DONE, &c->flags);
 		set_bit(BCH_FS_FSCK_DONE, &c->flags);
 
@@ -1417,6 +1441,9 @@ int bch2_fs_initialize(struct bch_fs *c)
 	c->disk_sb.sb->compat[0] |= cpu_to_le64(1ULL << BCH_COMPAT_extents_above_btree_updates_done);
 	c->disk_sb.sb->compat[0] |= cpu_to_le64(1ULL << BCH_COMPAT_bformat_overflow_done);
 
+	if (c->sb.version < bcachefs_metadata_version_backpointers)
+		c->opts.version_upgrade	= true;
+
 	if (c->opts.version_upgrade) {
 		c->disk_sb.sb->version = cpu_to_le16(bcachefs_metadata_version_current);
 		c->disk_sb.sb->features[0] |= cpu_to_le64(BCH_SB_FEATURES_ALL);
diff --git a/libbcachefs/super.c b/libbcachefs/super.c
index 71fc231d..29089740 100644
--- a/libbcachefs/super.c
+++ b/libbcachefs/super.c
@@ -1433,6 +1433,8 @@ static int bch2_dev_remove_alloc(struct bch_fs *c, struct bch_dev *ca)
 					BTREE_TRIGGER_NORUN, NULL) ?:
 		bch2_btree_delete_range(c, BTREE_ID_freespace, start, end,
 					BTREE_TRIGGER_NORUN, NULL) ?:
+		bch2_btree_delete_range(c, BTREE_ID_backpointers, start, end,
+					BTREE_TRIGGER_NORUN, NULL) ?:
 		bch2_btree_delete_range(c, BTREE_ID_alloc, start, end,
 					BTREE_TRIGGER_NORUN, NULL);
 	if (ret)