X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=libbcachefs%2Fbackpointers.c;h=23fe9378fb40aa76d39d58e176614de50bd078e1;hb=HEAD;hp=614811eafa59f409568e29758746c3d3d75b0912;hpb=c1e4d447f6dd0ee60495b651436d2055db7777ed;p=bcachefs-tools-debian

diff --git a/libbcachefs/backpointers.c b/libbcachefs/backpointers.c
index 614811e..23fe937 100644
--- a/libbcachefs/backpointers.c
+++ b/libbcachefs/backpointers.c
@@ -3,44 +3,15 @@
 #include "bbpos.h"
 #include "alloc_background.h"
 #include "backpointers.h"
+#include "bkey_buf.h"
 #include "btree_cache.h"
 #include "btree_update.h"
+#include "btree_update_interior.h"
+#include "btree_write_buffer.h"
 #include "error.h"
 
 #include <linux/mm.h>
 
-/*
- * 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);
-	struct bpos ret;
-
-	ret = POS(bucket.inode,
-		  (bucket_to_sector(ca, bucket.offset) <<
-		   MAX_EXTENT_COMPRESS_RATIO_SHIFT) + bucket_offset);
-
-	BUG_ON(bkey_cmp(bucket, bp_pos_to_bucket(c, ret)));
-
-	return ret;
-}
-
 static bool extent_matches_bp(struct bch_fs *c,
 			      enum btree_id btree_id, unsigned level,
 			      struct bkey_s_c k,
@@ -60,7 +31,7 @@ static bool extent_matches_bp(struct bch_fs *c,
 
 		bch2_extent_ptr_to_bp(c, btree_id, level, k, p,
 				      &bucket2, &bp2);
-		if (!bpos_cmp(bucket, bucket2) &&
+		if (bpos_eq(bucket, bucket2) &&
 		    !memcmp(&bp, &bp2, sizeof(bp)))
 			return true;
 	}
@@ -68,29 +39,26 @@ static bool extent_matches_bp(struct bch_fs *c,
 	return false;
 }
 
-int bch2_backpointer_invalid(const struct bch_fs *c, struct bkey_s_c k,
-			     int rw, struct printbuf *err)
+int bch2_backpointer_invalid(struct bch_fs *c, struct bkey_s_c k,
+			     enum bkey_invalid_flags flags,
+			     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);
+	int ret = 0;
 
-	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;
+	bkey_fsck_err_on(!bpos_eq(bp.k->p, bucket_pos_to_bp(c, bucket, bp.v->bucket_offset)),
+			 c, err,
+			 backpointer_pos_wrong,
+			 "backpointer at wrong pos");
+fsck_err:
+	return ret;
 }
 
 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],
+	       bch2_btree_id_str(bp->btree_id),
 	       bp->level,
 	       (u64) (bp->bucket_offset >> MAX_EXTENT_COMPRESS_RATIO_SHIFT),
 	       (u32) bp->bucket_offset & ~(~0U << MAX_EXTENT_COMPRESS_RATIO_SHIFT),
@@ -100,6 +68,10 @@ void bch2_backpointer_to_text(struct printbuf *out, const struct bch_backpointer
 
 void bch2_backpointer_k_to_text(struct printbuf *out, struct bch_fs *c, struct bkey_s_c k)
 {
+	prt_str(out, "bucket=");
+	bch2_bpos_to_text(out, bp_pos_to_bucket(c, k.k->p));
+	prt_str(out, " ");
+
 	bch2_backpointer_to_text(out, bkey_s_c_to_backpointer(k).v);
 }
 
@@ -107,141 +79,35 @@ 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_offset	= swab40(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)
+static noinline int backpointer_mod_err(struct btree_trans *trans,
+					struct bch_backpointer bp,
+					struct bkey_s_c bp_k,
+					struct bkey_s_c orig_k,
+					bool insert)
 {
 	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;
+	struct printbuf buf = PRINTBUF;
 
-	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;
-	}
+	if (insert) {
+		prt_printf(&buf, "existing backpointer found when inserting ");
+		bch2_backpointer_to_text(&buf, &bp);
+		prt_newline(&buf);
+		printbuf_indent_add(&buf, 2);
 
-	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;
+		prt_printf(&buf, "found ");
+		bch2_bkey_val_to_text(&buf, c, bp_k);
+		prt_newline(&buf);
 
-	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, "for ");
+		bch2_bkey_val_to_text(&buf, c, orig_k);
 
+		bch_err(c, "%s", buf.buf);
+	} else if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
 		prt_printf(&buf, "backpointer not found when deleting");
 		prt_newline(&buf);
 		printbuf_indent_add(&buf, 2);
@@ -251,132 +117,65 @@ btree:
 		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));
+		bch2_bkey_val_to_text(&buf, c, bp_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 {
-			ret = -EIO;
-			bch2_trans_inconsistent(trans, "%s", buf.buf);
-		}
-		printbuf_exit(&buf);
-		goto err;
+		bch_err(c, "%s", buf.buf);
 	}
 
-	ret = bch2_btree_delete_at(trans, &bp_iter, 0);
-err:
-	bch2_trans_iter_exit(trans, &bp_iter);
-	return ret;
+	printbuf_exit(&buf);
+
+	if (c->curr_recovery_pass > BCH_RECOVERY_PASS_check_extents_to_backpointers) {
+		return bch2_inconsistent_error(c) ? BCH_ERR_erofs_unfixed_errors : 0;
+	} else {
+		return 0;
+	}
 }
 
-int bch2_bucket_backpointer_add(struct btree_trans *trans,
-				struct bkey_i_alloc_v4 *a,
+int bch2_bucket_backpointer_mod_nowritebuffer(struct btree_trans *trans,
+				struct bpos bucket,
 				struct bch_backpointer bp,
-				struct bkey_s_c orig_k)
+				struct bkey_s_c orig_k,
+				bool insert)
 {
-	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;
+	struct bkey_i_backpointer *bp_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));
+	bp_k = bch2_trans_kmalloc_nomemzero(trans, sizeof(struct bkey_i_backpointer));
 	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->k.p = bucket_pos_to_bp(trans->c, bucket, 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);
+	if (!insert) {
+		bp_k->k.type = KEY_TYPE_deleted;
+		set_bkey_val_u64s(&bp_k->k, 0);
+	}
+
+	k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
+			       bp_k->k.p,
+			       BTREE_ITER_INTENT|
+			       BTREE_ITER_SLOTS|
+			       BTREE_ITER_WITH_UPDATES);
 	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;
+	if (insert
+	    ? k.k->type
+	    : (k.k->type != KEY_TYPE_backpointer ||
+	       memcmp(bkey_s_c_to_backpointer(k).v, &bp, sizeof(bp)))) {
+		ret = backpointer_mod_err(trans, bp, k, orig_k, insert);
+		if (ret)
 			goto err;
-		}
 	}
 
 	ret = bch2_trans_update(trans, &bp_iter, &bp_k->k_i, 0);
@@ -390,62 +189,44 @@ err:
  */
 int bch2_get_next_backpointer(struct btree_trans *trans,
 			      struct bpos bucket, int gen,
-			      u64 *bp_offset,
-			      struct bch_backpointer *dst,
+			      struct bpos *bp_pos,
+			      struct bch_backpointer *bp,
 			      unsigned iter_flags)
 {
 	struct bch_fs *c = trans->c;
-	struct bpos bp_pos, bp_end_pos;
-	struct btree_iter alloc_iter, bp_iter = { NULL };
+	struct bpos bp_end_pos = bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
+	struct btree_iter alloc_iter = { NULL }, bp_iter = { NULL };
 	struct bkey_s_c k;
-	struct bkey_s_c_alloc_v4 a;
-	size_t i;
-	int ret;
-
-	if (*bp_offset == U64_MAX)
-		return 0;
-
-	bp_pos = bucket_pos_to_bp(c, bucket,
-				  max(*bp_offset, BACKPOINTER_OFFSET_MAX) - BACKPOINTER_OFFSET_MAX);
-	bp_end_pos = bucket_pos_to_bp(c, bpos_nosnap_successor(bucket), 0);
-
-	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;
+	int ret = 0;
 
-	a = bkey_s_c_to_alloc_v4(k);
-	if (gen >= 0 && a.v->gen != gen)
+	if (bpos_ge(*bp_pos, bp_end_pos))
 		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;
+	if (gen >= 0) {
+		k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
+				       bucket, BTREE_ITER_CACHED|iter_flags);
+		ret = bkey_err(k);
+		if (ret)
+			goto out;
 
-		*dst = alloc_v4_backpointers_c(a.v)[i];
-		*bp_offset = dst->bucket_offset;
-		goto out;
+		if (k.k->type != KEY_TYPE_alloc_v4 ||
+		    bkey_s_c_to_alloc_v4(k).v->gen != gen)
+			goto done;
 	}
 
+	*bp_pos = bpos_max(*bp_pos, bucket_pos_to_bp(c, bucket, 0));
+
 	for_each_btree_key_norestart(trans, bp_iter, BTREE_ID_backpointers,
-				     bp_pos, 0, k, ret) {
-		if (bpos_cmp(k.k->p, bp_end_pos) >= 0)
+				     *bp_pos, iter_flags, k, ret) {
+		if (bpos_ge(k.k->p, bp_end_pos))
 			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;
+		*bp_pos = k.k->p;
+		*bp = *bkey_s_c_to_backpointer(k).v;
 		goto out;
 	}
 done:
-	*bp_offset = U64_MAX;
+	*bp_pos = SPOS_MAX;
 out:
 	bch2_trans_iter_exit(trans, &bp_iter);
 	bch2_trans_iter_exit(trans, &alloc_iter);
@@ -453,34 +234,36 @@ out:
 }
 
 static void backpointer_not_found(struct btree_trans *trans,
-				  struct bpos bucket,
-				  u64 bp_offset,
+				  struct bpos bp_pos,
 				  struct bch_backpointer bp,
-				  struct bkey_s_c k,
-				  const char *thing_it_points_to)
+				  struct bkey_s_c k)
 {
 	struct bch_fs *c = trans->c;
 	struct printbuf buf = PRINTBUF;
+	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
+
+	/*
+	 * If we're using the btree write buffer, the backpointer we were
+	 * looking at may have already been deleted - failure to find what it
+	 * pointed to is not an error:
+	 */
+	if (likely(!bch2_backpointers_no_use_write_buffer))
+		return;
 
 	prt_printf(&buf, "backpointer doesn't match %s it points to:\n  ",
-		   thing_it_points_to);
+		   bp.level ? "btree node" : "extent");
 	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  ");
-	}
+	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))
+	if (c->curr_recovery_pass >= BCH_RECOVERY_PASS_check_extents_to_backpointers)
 		bch_err_ratelimited(c, "%s", buf.buf);
 	else
 		bch2_trans_inconsistent(trans, "%s", buf.buf);
@@ -490,64 +273,50 @@ static void backpointer_not_found(struct btree_trans *trans,
 
 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 bpos bp_pos,
+					 struct bch_backpointer bp,
+					 unsigned iter_flags)
 {
-	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 (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
-		return k;
-
-	bch2_trans_iter_exit(trans, iter);
-
-	if (bp.level) {
-		struct btree *b;
+	if (likely(!bp.level)) {
+		struct bch_fs *c = trans->c;
+		struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
+		struct bkey_s_c k;
+
+		bch2_trans_node_iter_init(trans, iter,
+					  bp.btree_id,
+					  bp.pos,
+					  0, 0,
+					  iter_flags);
+		k = bch2_btree_iter_peek_slot(iter);
+		if (bkey_err(k)) {
+			bch2_trans_iter_exit(trans, iter);
+			return k;
+		}
 
-		/*
-		 * If a backpointer for a btree node wasn't found, it may be
-		 * because it was overwritten by a new btree node that hasn't
-		 * been written out yet - backpointer_get_node() checks for
-		 * this:
-		 */
-		b = bch2_backpointer_get_node(trans, iter, bucket, bp_offset, bp);
-		if (!IS_ERR_OR_NULL(b))
-			return bkey_i_to_s_c(&b->key);
+		if (k.k && extent_matches_bp(c, bp.btree_id, bp.level, k, bucket, bp))
+			return k;
 
 		bch2_trans_iter_exit(trans, iter);
-
-		if (IS_ERR(b))
-			return bkey_s_c_err(PTR_ERR(b));
+		backpointer_not_found(trans, bp_pos, bp, k);
 		return bkey_s_c_null;
-	}
+	} else {
+		struct btree *b = bch2_backpointer_get_node(trans, iter, bp_pos, bp);
 
-	backpointer_not_found(trans, bucket, bp_offset, bp, k, "extent");
-	return bkey_s_c_null;
+		if (IS_ERR_OR_NULL(b)) {
+			bch2_trans_iter_exit(trans, iter);
+			return IS_ERR(b) ? bkey_s_c_err(PTR_ERR(b)) : bkey_s_c_null;
+		}
+		return bkey_i_to_s_c(&b->key);
+	}
 }
 
 struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
 					struct btree_iter *iter,
-					struct bpos bucket,
-					u64 bp_offset,
+					struct bpos bp_pos,
 					struct bch_backpointer bp)
 {
 	struct bch_fs *c = trans->c;
+	struct bpos bucket = bp_pos_to_bucket(c, bp_pos);
 	struct btree *b;
 
 	BUG_ON(!bp.level);
@@ -559,19 +328,20 @@ struct btree *bch2_backpointer_get_node(struct btree_trans *trans,
 				  bp.level - 1,
 				  0);
 	b = bch2_btree_iter_peek_node(iter);
-	if (IS_ERR(b))
+	if (IS_ERR_OR_NULL(b))
 		goto err;
 
-	if (b && extent_matches_bp(c, bp.btree_id, bp.level,
-				   bkey_i_to_s_c(&b->key),
-				   bucket, bp))
+	BUG_ON(b->c.level != bp.level - 1);
+
+	if (extent_matches_bp(c, bp.btree_id, bp.level,
+			      bkey_i_to_s_c(&b->key),
+			      bucket, bp))
 		return b;
 
-	if (b && btree_node_will_make_reachable(b)) {
+	if (btree_node_will_make_reachable(b)) {
 		b = ERR_PTR(-BCH_ERR_backpointer_to_overwritten_btree_node);
 	} else {
-		backpointer_not_found(trans, bucket, bp_offset, bp,
-				      bkey_i_to_s_c(&b->key), "btree node");
+		backpointer_not_found(trans, bp_pos, bp, bkey_i_to_s_c(&b->key));
 		b = NULL;
 	}
 err:
@@ -584,29 +354,26 @@ static int bch2_check_btree_backpointer(struct btree_trans *trans, struct btree_
 {
 	struct bch_fs *c = trans->c;
 	struct btree_iter alloc_iter = { NULL };
-	struct bch_dev *ca;
 	struct bkey_s_c alloc_k;
 	struct printbuf buf = PRINTBUF;
 	int ret = 0;
 
 	if (fsck_err_on(!bch2_dev_exists2(c, k.k->p.inode), c,
-			"backpointer for mising device:\n%s",
+			backpointer_to_missing_device,
+			"backpointer for missing 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);
+	alloc_k = bch2_bkey_get_iter(trans, &alloc_iter, BTREE_ID_alloc,
+				     bp_pos_to_bucket(c, k.k->p), 0);
 	ret = bkey_err(alloc_k);
 	if (ret)
 		goto out;
 
 	if (fsck_err_on(alloc_k.k->type != KEY_TYPE_alloc_v4, c,
+			backpointer_to_missing_alloc,
 			"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))) {
@@ -623,113 +390,109 @@ fsck_err:
 /* verify that every backpointer has a corresponding alloc key */
 int bch2_check_btree_backpointers(struct bch_fs *c)
 {
-	struct btree_iter iter;
-	struct bkey_s_c k;
-
-	return bch2_trans_run(c,
-		for_each_btree_key_commit(&trans, iter,
+	int ret = bch2_trans_run(c,
+		for_each_btree_key_commit(trans, iter,
 			BTREE_ID_backpointers, POS_MIN, 0, k,
-			NULL, NULL, BTREE_INSERT_LAZY_RW|BTREE_INSERT_NOFAIL,
-		  bch2_check_btree_backpointer(&trans, &iter, k)));
+			NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+		  bch2_check_btree_backpointer(trans, &iter, k)));
+	bch_err_fn(c, ret);
+	return ret;
+}
+
+static inline bool bkey_and_val_eq(struct bkey_s_c l, struct bkey_s_c r)
+{
+	return bpos_eq(l.k->p, r.k->p) &&
+		bkey_bytes(l.k) == bkey_bytes(r.k) &&
+		!memcmp(l.v, r.v, bkey_val_bytes(l.k));
 }
 
+struct extents_to_bp_state {
+	struct bpos	bucket_start;
+	struct bpos	bucket_end;
+	struct bkey_buf last_flushed;
+};
+
 static int check_bp_exists(struct btree_trans *trans,
-			   struct bpos bucket_pos,
+			   struct extents_to_bp_state *s,
+			   struct bpos bucket,
 			   struct bch_backpointer bp,
-			   struct bkey_s_c orig_k,
-			   struct bpos bucket_start,
-			   struct bpos bucket_end)
+			   struct bkey_s_c orig_k)
 {
 	struct bch_fs *c = trans->c;
-	struct btree_iter alloc_iter, bp_iter = { NULL };
+	struct btree_iter bp_iter = { NULL };
 	struct printbuf buf = PRINTBUF;
-	struct bkey_s_c alloc_k, bp_k;
+	struct bkey_s_c bp_k;
+	struct bkey_buf tmp;
 	int ret;
 
-	if (bpos_cmp(bucket_pos, bucket_start) < 0 ||
-	    bpos_cmp(bucket_pos, bucket_end) > 0)
-		return 0;
+	bch2_bkey_buf_init(&tmp);
 
-	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 (bpos_lt(bucket, s->bucket_start) ||
+	    bpos_gt(bucket, s->bucket_end))
+		return 0;
 
-	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 {
+	if (!bch2_dev_bucket_exists(c, bucket))
 		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);
+	bp_k = bch2_bkey_get_iter(trans, &bp_iter, BTREE_ID_backpointers,
+				  bucket_pos_to_bp(c, bucket, bp.bucket_offset),
+				  0);
 	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)))
+	    memcmp(bkey_s_c_to_backpointer(bp_k).v, &bp, sizeof(bp))) {
+		bch2_bkey_buf_reassemble(&tmp, c, orig_k);
+
+		if (!bkey_and_val_eq(orig_k, bkey_i_to_s_c(s->last_flushed.k))) {
+			if (bp.level) {
+				bch2_trans_unlock(trans);
+				bch2_btree_interior_updates_flush(c);
+			}
+
+			ret = bch2_btree_write_buffer_flush_sync(trans);
+			if (ret)
+				goto err;
+
+			bch2_bkey_buf_copy(&s->last_flushed, c, tmp.k);
+			ret = -BCH_ERR_transaction_restart_write_buffer_flush;
+			goto out;
+		}
 		goto missing;
+	}
 out:
 err:
 fsck_err:
 	bch2_trans_iter_exit(trans, &bp_iter);
-	bch2_trans_iter_exit(trans, &alloc_iter);
+	bch2_bkey_buf_exit(&tmp, c);
 	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_btree_id_str(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);
+	prt_printf(&buf, "\nbp pos ");
+	bch2_bpos_to_text(&buf, bp_iter.pos);
 
-	if (c->sb.version < bcachefs_metadata_version_backpointers ||
-	    c->opts.reconstruct_alloc ||
-	    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);
-	}
+	if (c->opts.reconstruct_alloc ||
+	    fsck_err(c, ptr_to_missing_backpointer, "%s", buf.buf))
+		ret = bch2_bucket_backpointer_mod(trans, bucket, bp, orig_k, true);
 
 	goto out;
 }
 
 static int check_extent_to_backpointers(struct btree_trans *trans,
-					struct btree_iter *iter,
-					struct bpos bucket_start,
-					struct bpos bucket_end)
+					struct extents_to_bp_state *s,
+					enum btree_id btree, unsigned level,
+					struct bkey_s_c k)
 {
 	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;
@@ -738,10 +501,10 @@ static int check_extent_to_backpointers(struct btree_trans *trans,
 		if (p.ptr.cached)
 			continue;
 
-		bch2_extent_ptr_to_bp(c, iter->btree_id, iter->path->level,
+		bch2_extent_ptr_to_bp(c, btree, level,
 				      k, p, &bucket_pos, &bp);
 
-		ret = check_bp_exists(trans, bucket_pos, bp, k, bucket_start, bucket_end);
+		ret = check_bp_exists(trans, s, bucket_pos, bp, k);
 		if (ret)
 			return ret;
 	}
@@ -750,44 +513,32 @@ static int check_extent_to_backpointers(struct btree_trans *trans,
 }
 
 static int check_btree_root_to_backpointers(struct btree_trans *trans,
+					    struct extents_to_bp_state *s,
 					    enum btree_id btree_id,
-					    struct bpos bucket_start,
-					    struct bpos bucket_end)
+					    int *level)
 {
 	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);
+retry:
+	bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN,
+				  0, bch2_btree_id_root(c, btree_id)->b->c.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;
+	if (b != btree_node_root(c, b)) {
+		bch2_trans_iter_exit(trans, &iter);
+		goto retry;
+	}
 
-		bch2_extent_ptr_to_bp(c, iter.btree_id, iter.path->level + 1,
-				      k, p, &bucket_pos, &bp);
+	*level = b->c.level;
 
-		ret = check_bp_exists(trans, bucket_pos, bp, k, bucket_start, bucket_end);
-		if (ret)
-			goto err;
-	}
+	k = bkey_i_to_s_c(&b->key);
+	ret = check_extent_to_backpointers(trans, s, btree_id, b->c.level + 1, k);
 err:
 	bch2_trans_iter_exit(trans, &iter);
 	return ret;
@@ -801,232 +552,214 @@ static inline struct bbpos bp_to_bbpos(struct bch_backpointer bp)
 	};
 }
 
-static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
+static u64 mem_may_pin_bytes(struct bch_fs *c)
 {
 	struct sysinfo i;
-	u64 mem_bytes;
-
 	si_meminfo(&i);
-	mem_bytes = i.totalram * i.mem_unit;
-	return (mem_bytes >> 1) / btree_bytes(c);
+
+	u64 mem_bytes = i.totalram * i.mem_unit;
+	return div_u64(mem_bytes * c->opts.fsck_memory_usage_percent, 100);
 }
 
-int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
-				 unsigned btree_leaf_mask,
-				 unsigned btree_interior_mask,
-				 struct bbpos start, struct bbpos *end)
+static size_t btree_nodes_fit_in_ram(struct bch_fs *c)
 {
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
-	enum btree_id btree;
+	return div_u64(mem_may_pin_bytes(c), c->opts.btree_node_size);
+}
+
+static int bch2_get_btree_in_memory_pos(struct btree_trans *trans,
+					u64 btree_leaf_mask,
+					u64 btree_interior_mask,
+					struct bbpos start, struct bbpos *end)
+{
+	struct bch_fs *c = trans->c;
+	s64 mem_may_pin = mem_may_pin_bytes(c);
 	int ret = 0;
 
-	for (btree = start.btree; btree < BTREE_ID_NR && !ret; btree++) {
-		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 1 : 2;
+	btree_interior_mask |= btree_leaf_mask;
+
+	c->btree_cache.pinned_nodes_leaf_mask		= btree_leaf_mask;
+	c->btree_cache.pinned_nodes_interior_mask	= btree_interior_mask;
+	c->btree_cache.pinned_nodes_start		= start;
+	c->btree_cache.pinned_nodes_end			= *end = BBPOS_MAX;
+
+	for (enum btree_id btree = start.btree;
+	     btree < BTREE_ID_NR && !ret;
+	     btree++) {
+		unsigned depth = ((1U << btree) & btree_leaf_mask) ? 0 : 1;
+		struct btree_iter iter;
+		struct btree *b;
 
 		if (!((1U << btree) & btree_leaf_mask) &&
 		    !((1U << btree) & btree_interior_mask))
 			continue;
 
-		bch2_trans_node_iter_init(trans, &iter, btree,
-					  btree == start.btree ? start.pos : POS_MIN,
-					  0, depth, 0);
-		/*
-		 * for_each_btree_key_contineu() doesn't check the return value
-		 * from bch2_btree_iter_advance(), which is needed when
-		 * iterating over interior nodes where we'll see keys at
-		 * SPOS_MAX:
-		 */
-		do {
-			k = __bch2_btree_iter_peek_and_restart(trans, &iter, 0);
-			ret = bkey_err(k);
-			if (!k.k || ret)
-				break;
-
-			--btree_nodes;
-			if (!btree_nodes) {
-				*end = BBPOS(btree, k.k->p);
+		__for_each_btree_node(trans, iter, btree,
+				      btree == start.btree ? start.pos : POS_MIN,
+				      0, depth, BTREE_ITER_PREFETCH, b, ret) {
+			mem_may_pin -= btree_buf_bytes(b);
+			if (mem_may_pin <= 0) {
+				c->btree_cache.pinned_nodes_end = *end =
+					BBPOS(btree, b->key.k.p);
 				bch2_trans_iter_exit(trans, &iter);
 				return 0;
 			}
-		} while (bch2_btree_iter_advance(&iter));
+		}
 		bch2_trans_iter_exit(trans, &iter);
 	}
 
-	*end = BBPOS_MAX;
 	return ret;
 }
 
 static int bch2_check_extents_to_backpointers_pass(struct btree_trans *trans,
-						   struct bpos bucket_start,
-						   struct bpos bucket_end)
+						   struct extents_to_bp_state *s)
 {
-	struct btree_iter iter;
-	enum btree_id btree_id;
+	struct bch_fs *c = trans->c;
 	int ret = 0;
 
-	for (btree_id = 0; btree_id < BTREE_ID_NR; btree_id++) {
-		unsigned depth = btree_type_has_ptrs(btree_id) ? 0 : 1;
-
-		bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
-					  depth,
-					  BTREE_ITER_ALL_LEVELS|
-					  BTREE_ITER_PREFETCH);
-
-		do {
-			ret = commit_do(trans, NULL, NULL,
-					BTREE_INSERT_LAZY_RW|
-					BTREE_INSERT_NOFAIL,
-					check_extent_to_backpointers(trans, &iter,
-								bucket_start, bucket_end));
-			if (ret)
-				break;
-		} while (!bch2_btree_iter_advance(&iter));
-
-		bch2_trans_iter_exit(trans, &iter);
-
-		if (ret)
-			break;
+	for (enum btree_id btree_id = 0;
+	     btree_id < btree_id_nr_alive(c);
+	     btree_id++) {
+		int level, depth = btree_type_has_ptrs(btree_id) ? 0 : 1;
 
 		ret = commit_do(trans, NULL, NULL,
-				BTREE_INSERT_LAZY_RW|
-				BTREE_INSERT_NOFAIL,
-				check_btree_root_to_backpointers(trans, btree_id,
-							bucket_start, bucket_end));
+				BCH_TRANS_COMMIT_no_enospc,
+				check_btree_root_to_backpointers(trans, s, btree_id, &level));
 		if (ret)
-			break;
-	}
-	return ret;
-}
-
-int bch2_get_alloc_in_memory_pos(struct btree_trans *trans,
-				 struct bpos start, struct bpos *end)
-{
-	struct btree_iter alloc_iter;
-	struct btree_iter bp_iter;
-	struct bkey_s_c alloc_k, bp_k;
-	size_t btree_nodes = btree_nodes_fit_in_ram(trans->c);
-	bool alloc_end = false, bp_end = false;
-	int ret = 0;
+			return ret;
 
-	bch2_trans_node_iter_init(trans, &alloc_iter, BTREE_ID_alloc,
-				  start, 0, 1, 0);
-	bch2_trans_node_iter_init(trans, &bp_iter, BTREE_ID_backpointers,
-				  bucket_pos_to_bp(trans->c, start, 0), 0, 1, 0);
-	while (1) {
-		alloc_k = !alloc_end
-			? __bch2_btree_iter_peek_and_restart(trans, &alloc_iter, 0)
-			: bkey_s_c_null;
-		bp_k = !bp_end
-			? __bch2_btree_iter_peek_and_restart(trans, &bp_iter, 0)
-			: bkey_s_c_null;
-
-		ret = bkey_err(alloc_k) ?: bkey_err(bp_k);
-		if ((!alloc_k.k && !bp_k.k) || ret) {
-			*end = SPOS_MAX;
-			break;
-		}
+		while (level >= depth) {
+			struct btree_iter iter;
+			bch2_trans_node_iter_init(trans, &iter, btree_id, POS_MIN, 0,
+						  level,
+						  BTREE_ITER_PREFETCH);
+			while (1) {
+				bch2_trans_begin(trans);
+
+				struct bkey_s_c k = bch2_btree_iter_peek(&iter);
+				if (!k.k)
+					break;
+				ret = bkey_err(k) ?:
+					check_extent_to_backpointers(trans, s, btree_id, level, k) ?:
+					bch2_trans_commit(trans, NULL, NULL,
+							  BCH_TRANS_COMMIT_no_enospc);
+				if (bch2_err_matches(ret, BCH_ERR_transaction_restart)) {
+					ret = 0;
+					continue;
+				}
+				if (ret)
+					break;
+				if (bpos_eq(iter.pos, SPOS_MAX))
+					break;
+				bch2_btree_iter_advance(&iter);
+			}
+			bch2_trans_iter_exit(trans, &iter);
 
-		--btree_nodes;
-		if (!btree_nodes) {
-			*end = alloc_k.k->p;
-			break;
-		}
+			if (ret)
+				return ret;
 
-		if (bpos_cmp(alloc_iter.pos, SPOS_MAX) &&
-		    bpos_cmp(bucket_pos_to_bp(trans->c, alloc_iter.pos, 0), bp_iter.pos) < 0) {
-			if (!bch2_btree_iter_advance(&alloc_iter))
-				alloc_end = true;
-		} else {
-			if (!bch2_btree_iter_advance(&bp_iter))
-				bp_end = true;
+			--level;
 		}
 	}
-	bch2_trans_iter_exit(trans, &bp_iter);
-	bch2_trans_iter_exit(trans, &alloc_iter);
-	return ret;
+
+	return 0;
 }
 
 int bch2_check_extents_to_backpointers(struct bch_fs *c)
 {
-	struct btree_trans trans;
-	struct bpos start = POS_MIN, end;
+	struct btree_trans *trans = bch2_trans_get(c);
+	struct extents_to_bp_state s = { .bucket_start = POS_MIN };
 	int ret;
 
-	bch2_trans_init(&trans, c, 0, 0);
+	bch2_bkey_buf_init(&s.last_flushed);
+	bkey_init(&s.last_flushed.k->k);
+
 	while (1) {
-		ret = bch2_get_alloc_in_memory_pos(&trans, start, &end);
+		struct bbpos end;
+		ret = bch2_get_btree_in_memory_pos(trans,
+				BIT_ULL(BTREE_ID_backpointers),
+				BIT_ULL(BTREE_ID_backpointers),
+				BBPOS(BTREE_ID_backpointers, s.bucket_start), &end);
 		if (ret)
 			break;
 
-		if (!bpos_cmp(start, POS_MIN) && bpos_cmp(end, SPOS_MAX))
+		s.bucket_end = end.pos;
+
+		if ( bpos_eq(s.bucket_start, POS_MIN) &&
+		    !bpos_eq(s.bucket_end, SPOS_MAX))
 			bch_verbose(c, "%s(): alloc info does not fit in ram, running in multiple passes with %zu nodes per pass",
 				    __func__, btree_nodes_fit_in_ram(c));
 
-		if (bpos_cmp(start, POS_MIN) || bpos_cmp(end, SPOS_MAX)) {
+		if (!bpos_eq(s.bucket_start, POS_MIN) ||
+		    !bpos_eq(s.bucket_end, SPOS_MAX)) {
 			struct printbuf buf = PRINTBUF;
 
 			prt_str(&buf, "check_extents_to_backpointers(): ");
-			bch2_bpos_to_text(&buf, start);
+			bch2_bpos_to_text(&buf, s.bucket_start);
 			prt_str(&buf, "-");
-			bch2_bpos_to_text(&buf, end);
+			bch2_bpos_to_text(&buf, s.bucket_end);
 
 			bch_verbose(c, "%s", buf.buf);
 			printbuf_exit(&buf);
 		}
 
-		ret = bch2_check_extents_to_backpointers_pass(&trans, start, end);
-		if (ret || !bpos_cmp(end, SPOS_MAX))
+		ret = bch2_check_extents_to_backpointers_pass(trans, &s);
+		if (ret || bpos_eq(s.bucket_end, SPOS_MAX))
 			break;
 
-		start = bpos_successor(end);
+		s.bucket_start = bpos_successor(s.bucket_end);
 	}
-	bch2_trans_exit(&trans);
+	bch2_trans_put(trans);
+	bch2_bkey_buf_exit(&s.last_flushed, c);
+
+	c->btree_cache.pinned_nodes_leaf_mask = 0;
+	c->btree_cache.pinned_nodes_interior_mask = 0;
 
+	bch_err_fn(c, ret);
 	return ret;
 }
 
 static int check_one_backpointer(struct btree_trans *trans,
-				 struct bpos bucket,
-				 u64 *bp_offset,
 				 struct bbpos start,
-				 struct bbpos end)
+				 struct bbpos end,
+				 struct bkey_s_c_backpointer bp,
+				 struct bpos *last_flushed_pos)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_iter iter;
-	struct bch_backpointer bp;
-	struct bbpos pos;
+	struct bbpos pos = bp_to_bbpos(*bp.v);
 	struct bkey_s_c k;
 	struct printbuf buf = PRINTBUF;
 	int ret;
 
-	ret = bch2_get_next_backpointer(trans, bucket, -1, bp_offset, &bp, 0);
-	if (ret || *bp_offset == U64_MAX)
-		return ret;
-
-	pos = bp_to_bbpos(bp);
 	if (bbpos_cmp(pos, start) < 0 ||
 	    bbpos_cmp(pos, end) > 0)
 		return 0;
 
-	k = bch2_backpointer_get_key(trans, &iter, bucket, *bp_offset, bp);
+	k = bch2_backpointer_get_key(trans, &iter, bp.k->p, *bp.v, 0);
 	ret = bkey_err(k);
 	if (ret == -BCH_ERR_backpointer_to_overwritten_btree_node)
 		return 0;
 	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);
+	if (!k.k && !bpos_eq(*last_flushed_pos, bp.k->p)) {
+		*last_flushed_pos = bp.k->p;
+		ret = bch2_btree_write_buffer_flush_sync(trans) ?:
+			-BCH_ERR_transaction_restart_write_buffer_flush;
+		goto out;
 	}
 
-	bch2_trans_iter_exit(trans, &iter);
+	if (fsck_err_on(!k.k, c,
+			backpointer_to_missing_ptr,
+			"backpointer for missing %s\n  %s",
+			bp.v->level ? "btree node" : "extent",
+			(bch2_bkey_val_to_text(&buf, c, bp.s_c), buf.buf))) {
+		ret = bch2_btree_delete_at_buffered(trans, BTREE_ID_backpointers, bp.k->p);
+		goto out;
+	}
+out:
 fsck_err:
+	bch2_trans_iter_exit(trans, &iter);
 	printbuf_exit(&buf);
 	return ret;
 }
@@ -1035,37 +768,24 @@ static int bch2_check_backpointers_to_extents_pass(struct btree_trans *trans,
 						   struct bbpos start,
 						   struct bbpos end)
 {
-	struct btree_iter iter;
-	struct bkey_s_c k;
-	int ret = 0;
-
-	for_each_btree_key(trans, iter, BTREE_ID_alloc, POS_MIN,
-			   BTREE_ITER_PREFETCH, k, ret) {
-		u64 bp_offset = 0;
-
-		while (!(ret = commit_do(trans, NULL, NULL,
-					 BTREE_INSERT_LAZY_RW|
-					 BTREE_INSERT_NOFAIL,
-				check_one_backpointer(trans, iter.pos, &bp_offset, start, end))) &&
-		       bp_offset < U64_MAX)
-			bp_offset++;
-
-		if (ret)
-			break;
-	}
-	bch2_trans_iter_exit(trans, &iter);
-	return ret < 0 ? ret : 0;
+	struct bpos last_flushed_pos = SPOS_MAX;
+
+	return for_each_btree_key_commit(trans, iter, BTREE_ID_backpointers,
+				  POS_MIN, BTREE_ITER_PREFETCH, k,
+				  NULL, NULL, BCH_TRANS_COMMIT_no_enospc,
+		check_one_backpointer(trans, start, end,
+				      bkey_s_c_to_backpointer(k),
+				      &last_flushed_pos));
 }
 
 int bch2_check_backpointers_to_extents(struct bch_fs *c)
 {
-	struct btree_trans trans;
+	struct btree_trans *trans = bch2_trans_get(c);
 	struct bbpos start = (struct bbpos) { .btree = 0, .pos = POS_MIN, }, end;
 	int ret;
 
-	bch2_trans_init(&trans, c, 0, 0);
 	while (1) {
-		ret = bch2_get_btree_in_memory_pos(&trans,
+		ret = bch2_get_btree_in_memory_pos(trans,
 						   (1U << BTREE_ID_extents)|
 						   (1U << BTREE_ID_reflink),
 						   ~0,
@@ -1091,13 +811,17 @@ int bch2_check_backpointers_to_extents(struct bch_fs *c)
 			printbuf_exit(&buf);
 		}
 
-		ret = bch2_check_backpointers_to_extents_pass(&trans, start, end);
+		ret = bch2_check_backpointers_to_extents_pass(trans, start, end);
 		if (ret || !bbpos_cmp(end, BBPOS_MAX))
 			break;
 
 		start = bbpos_successor(end);
 	}
-	bch2_trans_exit(&trans);
+	bch2_trans_put(trans);
+
+	c->btree_cache.pinned_nodes_leaf_mask = 0;
+	c->btree_cache.pinned_nodes_interior_mask = 0;
 
+	bch_err_fn(c, ret);
 	return ret;
 }