X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=libbcachefs%2Fbtree_gc.c;h=b02624992ab6c0a599b22f973e60cd5d6e1b21ad;hb=a76f36fc6e6af7a4ba8d440d84e2cd6b4ec0b88b;hp=6b67da90bcea160f5e1f51db60a8483eb300146a;hpb=cc6479303f0672d5e07899009c64eb32821e170b;p=bcachefs-tools-debian

diff --git a/libbcachefs/btree_gc.c b/libbcachefs/btree_gc.c
index 6b67da9..b026249 100644
--- a/libbcachefs/btree_gc.c
+++ b/libbcachefs/btree_gc.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Copyright (C) 2010 Kent Overstreet <kent.overstreet@gmail.com>
  * Copyright (C) 2014 Datera Inc.
@@ -7,6 +8,7 @@
 #include "alloc_background.h"
 #include "alloc_foreground.h"
 #include "bkey_methods.h"
+#include "bkey_buf.h"
 #include "btree_locking.h"
 #include "btree_update_interior.h"
 #include "btree_io.h"
@@ -14,12 +16,13 @@
 #include "buckets.h"
 #include "clock.h"
 #include "debug.h"
+#include "ec.h"
 #include "error.h"
 #include "extents.h"
 #include "journal.h"
-#include "journal_io.h"
 #include "keylist.h"
 #include "move.h"
+#include "recovery.h"
 #include "replicas.h"
 #include "super-io.h"
 
@@ -34,9 +37,11 @@
 
 static inline void __gc_pos_set(struct bch_fs *c, struct gc_pos new_pos)
 {
+	preempt_disable();
 	write_seqcount_begin(&c->gc_pos_lock);
 	c->gc_pos = new_pos;
 	write_seqcount_end(&c->gc_pos_lock);
+	preempt_enable();
 }
 
 static inline void gc_pos_set(struct bch_fs *c, struct gc_pos new_pos)
@@ -45,351 +50,859 @@ static inline void gc_pos_set(struct bch_fs *c, struct gc_pos new_pos)
 	__gc_pos_set(c, new_pos);
 }
 
-/* range_checks - for validating min/max pos of each btree node: */
+/*
+ * Missing: if an interior btree node is empty, we need to do something -
+ * perhaps just kill it
+ */
+static int bch2_gc_check_topology(struct bch_fs *c,
+				  struct btree *b,
+				  struct bkey_buf *prev,
+				  struct bkey_buf cur,
+				  bool is_last)
+{
+	struct bpos node_start	= b->data->min_key;
+	struct bpos node_end	= b->data->max_key;
+	struct bpos expected_start = bkey_deleted(&prev->k->k)
+		? node_start
+		: bpos_successor(prev->k->k.p);
+	char buf1[200], buf2[200];
+	int ret = 0;
 
-struct range_checks {
-	struct range_level {
-		struct bpos	min;
-		struct bpos	max;
-	}			l[BTREE_MAX_DEPTH];
-	unsigned		depth;
-};
+	if (cur.k->k.type == KEY_TYPE_btree_ptr_v2) {
+		struct bkey_i_btree_ptr_v2 *bp = bkey_i_to_btree_ptr_v2(cur.k);
 
-static void btree_node_range_checks_init(struct range_checks *r, unsigned depth)
-{
-	unsigned i;
+		if (bkey_deleted(&prev->k->k)) {
+			struct printbuf out = PBUF(buf1);
+			pr_buf(&out, "start of node: ");
+			bch2_bpos_to_text(&out, node_start);
+		} else {
+			bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(prev->k));
+		}
 
-	for (i = 0; i < BTREE_MAX_DEPTH; i++)
-		r->l[i].min = r->l[i].max = POS_MIN;
-	r->depth = depth;
+		if (bpos_cmp(expected_start, bp->v.min_key)) {
+			bch2_topology_error(c);
+
+			if (fsck_err(c, "btree node with incorrect min_key at btree %s level %u:\n"
+				     "  prev %s\n"
+				     "  cur %s",
+				     bch2_btree_ids[b->c.btree_id], b->c.level,
+				     buf1,
+				     (bch2_bkey_val_to_text(&PBUF(buf2), c, bkey_i_to_s_c(cur.k)), buf2))) {
+				bch_info(c, "Halting mark and sweep to start topology repair pass");
+				return FSCK_ERR_START_TOPOLOGY_REPAIR;
+			} else {
+				set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+			}
+		}
+	}
+
+	if (is_last && bpos_cmp(cur.k->k.p, node_end)) {
+		bch2_topology_error(c);
+
+		if (fsck_err(c, "btree node with incorrect max_key at btree %s level %u:\n"
+			     "  %s\n"
+			     "  expected %s",
+			     bch2_btree_ids[b->c.btree_id], b->c.level,
+			     (bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(cur.k)), buf1),
+			     (bch2_bpos_to_text(&PBUF(buf2), node_end), buf2))) {
+			bch_info(c, "Halting mark and sweep to start topology repair pass");
+			return FSCK_ERR_START_TOPOLOGY_REPAIR;
+		} else {
+			set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+		}
+	}
+
+	bch2_bkey_buf_copy(prev, c, cur.k);
+fsck_err:
+	return ret;
 }
 
-static void btree_node_range_checks(struct bch_fs *c, struct btree *b,
-				    struct range_checks *r)
+static void btree_ptr_to_v2(struct btree *b, struct bkey_i_btree_ptr_v2 *dst)
 {
-	struct range_level *l = &r->l[b->level];
-
-	struct bpos expected_min = bkey_cmp(l->min, l->max)
-		? btree_type_successor(b->btree_id, l->max)
-		: l->max;
-
-	bch2_fs_inconsistent_on(bkey_cmp(b->data->min_key, expected_min), c,
-		"btree node has incorrect min key: %llu:%llu != %llu:%llu",
-		b->data->min_key.inode,
-		b->data->min_key.offset,
-		expected_min.inode,
-		expected_min.offset);
-
-	l->max = b->data->max_key;
-
-	if (b->level > r->depth) {
-		l = &r->l[b->level - 1];
-
-		bch2_fs_inconsistent_on(bkey_cmp(b->data->min_key, l->min), c,
-			"btree node min doesn't match min of child nodes: %llu:%llu != %llu:%llu",
-			b->data->min_key.inode,
-			b->data->min_key.offset,
-			l->min.inode,
-			l->min.offset);
-
-		bch2_fs_inconsistent_on(bkey_cmp(b->data->max_key, l->max), c,
-			"btree node max doesn't match max of child nodes: %llu:%llu != %llu:%llu",
-			b->data->max_key.inode,
-			b->data->max_key.offset,
-			l->max.inode,
-			l->max.offset);
-
-		if (bkey_cmp(b->data->max_key, POS_MAX))
-			l->min = l->max =
-				btree_type_successor(b->btree_id,
-						     b->data->max_key);
+	switch (b->key.k.type) {
+	case KEY_TYPE_btree_ptr: {
+		struct bkey_i_btree_ptr *src = bkey_i_to_btree_ptr(&b->key);
+
+		dst->k.p		= src->k.p;
+		dst->v.mem_ptr		= 0;
+		dst->v.seq		= b->data->keys.seq;
+		dst->v.sectors_written	= 0;
+		dst->v.flags		= 0;
+		dst->v.min_key		= b->data->min_key;
+		set_bkey_val_bytes(&dst->k, sizeof(dst->v) + bkey_val_bytes(&src->k));
+		memcpy(dst->v.start, src->v.start, bkey_val_bytes(&src->k));
+		break;
+	}
+	case KEY_TYPE_btree_ptr_v2:
+		bkey_copy(&dst->k_i, &b->key);
+		break;
+	default:
+		BUG();
 	}
 }
 
-/* marking of btree keys/nodes: */
+static int set_node_min(struct bch_fs *c, struct btree *b, struct bpos new_min)
+{
+	struct bkey_i_btree_ptr_v2 *new;
+	int ret;
+
+	new = kmalloc(BKEY_BTREE_PTR_U64s_MAX * sizeof(u64), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	btree_ptr_to_v2(b, new);
+	b->data->min_key	= new_min;
+	new->v.min_key		= new_min;
+	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);
 
-static bool bkey_type_needs_gc(enum bkey_type type)
+	ret = bch2_journal_key_insert(c, b->c.btree_id, b->c.level + 1, &new->k_i);
+	if (ret) {
+		kfree(new);
+		return ret;
+	}
+
+	bch2_btree_node_drop_keys_outside_node(b);
+
+	return 0;
+}
+
+static int set_node_max(struct bch_fs *c, struct btree *b, struct bpos new_max)
 {
-	switch (type) {
-	case BKEY_TYPE_BTREE:
-	case BKEY_TYPE_EXTENTS:
-		return true;
-	default:
-		return false;
+	struct bkey_i_btree_ptr_v2 *new;
+	int ret;
+
+	ret = bch2_journal_key_delete(c, b->c.btree_id, b->c.level + 1, b->key.k.p);
+	if (ret)
+		return ret;
+
+	new = kmalloc(BKEY_BTREE_PTR_U64s_MAX * sizeof(u64), GFP_KERNEL);
+	if (!new)
+		return -ENOMEM;
+
+	btree_ptr_to_v2(b, new);
+	b->data->max_key	= new_max;
+	new->k.p		= new_max;
+	SET_BTREE_PTR_RANGE_UPDATED(&new->v, true);
+
+	ret = bch2_journal_key_insert(c, b->c.btree_id, b->c.level + 1, &new->k_i);
+	if (ret) {
+		kfree(new);
+		return ret;
 	}
+
+	bch2_btree_node_drop_keys_outside_node(b);
+
+	mutex_lock(&c->btree_cache.lock);
+	bch2_btree_node_hash_remove(&c->btree_cache, b);
+
+	bkey_copy(&b->key, &new->k_i);
+	ret = __bch2_btree_node_hash_insert(&c->btree_cache, b);
+	BUG_ON(ret);
+	mutex_unlock(&c->btree_cache.lock);
+	return 0;
 }
 
-static void ptr_gen_recalc_oldest(struct bch_fs *c,
-				  const struct bch_extent_ptr *ptr,
-				  u8 *max_stale)
+static int btree_repair_node_start(struct bch_fs *c, struct btree *b,
+				   struct btree *prev, struct btree *cur)
 {
-	struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
-	size_t b = PTR_BUCKET_NR(ca, ptr);
+	struct bpos expected_start = !prev
+		? b->data->min_key
+		: bpos_successor(prev->key.k.p);
+	char buf1[200], buf2[200];
+	int ret = 0;
 
-	if (gen_after(ca->oldest_gens[b], ptr->gen))
-		ca->oldest_gens[b] = ptr->gen;
+	if (!prev) {
+		struct printbuf out = PBUF(buf1);
+		pr_buf(&out, "start of node: ");
+		bch2_bpos_to_text(&out, b->data->min_key);
+	} else {
+		bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(&prev->key));
+	}
 
-	*max_stale = max(*max_stale, ptr_stale(ca, ptr));
+	if (mustfix_fsck_err_on(bpos_cmp(expected_start, cur->data->min_key), c,
+			"btree node with incorrect min_key at btree %s level %u:\n"
+			"  prev %s\n"
+			"  cur %s",
+			bch2_btree_ids[b->c.btree_id], b->c.level,
+			buf1,
+			(bch2_bkey_val_to_text(&PBUF(buf2), c, bkey_i_to_s_c(&cur->key)), buf2))) {
+		if (prev &&
+		    bpos_cmp(expected_start, cur->data->min_key) > 0 &&
+		    BTREE_NODE_SEQ(cur->data) > BTREE_NODE_SEQ(prev->data))
+			ret = set_node_max(c, prev,
+				bpos_predecessor(cur->data->min_key));
+		else
+			ret = set_node_min(c, cur, expected_start);
+		if (ret)
+			return ret;
+	}
+fsck_err:
+	return ret;
 }
 
-static u8 ptr_gens_recalc_oldest(struct bch_fs *c,
-				 enum bkey_type type,
-				 struct bkey_s_c k)
+static int btree_repair_node_end(struct bch_fs *c, struct btree *b,
+				 struct btree *child)
 {
-	const struct bch_extent_ptr *ptr;
-	u8 max_stale = 0;
+	char buf1[200], buf2[200];
+	int ret = 0;
 
-	switch (type) {
-	case BKEY_TYPE_BTREE:
-	case BKEY_TYPE_EXTENTS:
-		switch (k.k->type) {
-		case BCH_EXTENT:
-		case BCH_EXTENT_CACHED: {
-			struct bkey_s_c_extent e = bkey_s_c_to_extent(k);
+	if (mustfix_fsck_err_on(bpos_cmp(child->key.k.p, b->key.k.p), c,
+			"btree node with incorrect max_key at btree %s level %u:\n"
+			"  %s\n"
+			"  expected %s",
+			bch2_btree_ids[b->c.btree_id], b->c.level,
+			(bch2_bkey_val_to_text(&PBUF(buf1), c, bkey_i_to_s_c(&child->key)), buf1),
+			(bch2_bpos_to_text(&PBUF(buf2), b->key.k.p), buf2))) {
+		ret = set_node_max(c, child, b->key.k.p);
+		if (ret)
+			return ret;
+	}
+fsck_err:
+	return ret;
+}
+
+#define DROP_THIS_NODE		10
+
+static int bch2_btree_repair_topology_recurse(struct bch_fs *c, struct btree *b)
+{
+	struct btree_and_journal_iter iter;
+	struct bkey_s_c k;
+	struct bkey_buf tmp;
+	struct btree *prev = NULL, *cur = NULL;
+	bool have_child, dropped_children = false;
+	char buf[200];
+	int ret = 0;
+
+	if (!b->c.level)
+		return 0;
+again:
+	have_child = dropped_children = false;
+	bch2_bkey_buf_init(&tmp);
+	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+
+	while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+		bch2_btree_and_journal_iter_advance(&iter);
+		bch2_bkey_buf_reassemble(&tmp, c, k);
+
+		cur = bch2_btree_node_get_noiter(c, tmp.k,
+					b->c.btree_id, b->c.level - 1,
+					false);
+		ret = PTR_ERR_OR_ZERO(cur);
+
+		if (mustfix_fsck_err_on(ret == -EIO, c,
+				"Unreadable btree node at btree %s level %u:\n"
+				"  %s",
+				bch2_btree_ids[b->c.btree_id],
+				b->c.level - 1,
+				(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(tmp.k)), buf))) {
+			bch2_btree_node_evict(c, tmp.k);
+			ret = bch2_journal_key_delete(c, b->c.btree_id,
+						      b->c.level, tmp.k->k.p);
+			if (ret)
+				goto err;
+			continue;
+		}
+
+		if (ret) {
+			bch_err(c, "%s: error %i getting btree node",
+				__func__, ret);
+			break;
+		}
+
+		ret = btree_repair_node_start(c, b, prev, cur);
+		if (prev)
+			six_unlock_read(&prev->c.lock);
+		prev = cur;
+		cur = NULL;
 
-			extent_for_each_ptr(e, ptr)
-				ptr_gen_recalc_oldest(c, ptr, &max_stale);
+		if (ret)
 			break;
+	}
+
+	if (!ret && !IS_ERR_OR_NULL(prev)) {
+		BUG_ON(cur);
+		ret = btree_repair_node_end(c, b, prev);
+	}
+
+	if (!IS_ERR_OR_NULL(prev))
+		six_unlock_read(&prev->c.lock);
+	prev = NULL;
+	if (!IS_ERR_OR_NULL(cur))
+		six_unlock_read(&cur->c.lock);
+	cur = NULL;
+
+	if (ret)
+		goto err;
+
+	bch2_btree_and_journal_iter_exit(&iter);
+	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+
+	while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+		bch2_bkey_buf_reassemble(&tmp, c, k);
+		bch2_btree_and_journal_iter_advance(&iter);
+
+		cur = bch2_btree_node_get_noiter(c, tmp.k,
+					b->c.btree_id, b->c.level - 1,
+					false);
+		ret = PTR_ERR_OR_ZERO(cur);
+
+		if (ret) {
+			bch_err(c, "%s: error %i getting btree node",
+				__func__, ret);
+			goto err;
 		}
+
+		ret = bch2_btree_repair_topology_recurse(c, cur);
+		six_unlock_read(&cur->c.lock);
+		cur = NULL;
+
+		if (ret == DROP_THIS_NODE) {
+			bch2_btree_node_evict(c, tmp.k);
+			ret = bch2_journal_key_delete(c, b->c.btree_id,
+						      b->c.level, tmp.k->k.p);
+			dropped_children = true;
 		}
-		break;
-	default:
-		break;
+
+		if (ret)
+			goto err;
+
+		have_child = true;
 	}
 
-	return max_stale;
+	if (mustfix_fsck_err_on(!have_child, c,
+			"empty interior btree node at btree %s level %u\n"
+			"  %s",
+			bch2_btree_ids[b->c.btree_id],
+			b->c.level,
+			(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(&b->key)), buf)))
+		ret = DROP_THIS_NODE;
+err:
+fsck_err:
+	if (!IS_ERR_OR_NULL(prev))
+		six_unlock_read(&prev->c.lock);
+	if (!IS_ERR_OR_NULL(cur))
+		six_unlock_read(&cur->c.lock);
+
+	bch2_btree_and_journal_iter_exit(&iter);
+	bch2_bkey_buf_exit(&tmp, c);
+
+	if (!ret && dropped_children)
+		goto again;
+
+	return ret;
 }
 
-static int ptr_gen_check(struct bch_fs *c,
-			 enum bkey_type type,
-			 const struct bch_extent_ptr *ptr)
+static int bch2_repair_topology(struct bch_fs *c)
 {
-	struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
-	size_t b = PTR_BUCKET_NR(ca, ptr);
-	struct bucket *g = PTR_BUCKET(ca, ptr);
+	struct btree *b;
+	unsigned i;
 	int ret = 0;
 
-	if (mustfix_fsck_err_on(!g->mark.gen_valid, c,
-				"found ptr with missing gen in alloc btree,\n"
-				"type %u gen %u",
-				type, ptr->gen)) {
-		g->_mark.gen = ptr->gen;
-		g->_mark.gen_valid = 1;
-		set_bit(b, ca->buckets_dirty);
-	}
+	for (i = 0; i < BTREE_ID_NR && !ret; i++) {
+		b = c->btree_roots[i].b;
+		if (btree_node_fake(b))
+			continue;
+
+		six_lock_read(&b->c.lock, NULL, NULL);
+		ret = bch2_btree_repair_topology_recurse(c, b);
+		six_unlock_read(&b->c.lock);
 
-	if (mustfix_fsck_err_on(gen_cmp(ptr->gen, g->mark.gen) > 0, c,
-				"%u ptr gen in the future: %u > %u",
-				type, ptr->gen, g->mark.gen)) {
-		g->_mark.gen = ptr->gen;
-		g->_mark.gen_valid = 1;
-		set_bit(b, ca->buckets_dirty);
-		set_bit(BCH_FS_FIXED_GENS, &c->flags);
+		if (ret == DROP_THIS_NODE) {
+			bch_err(c, "empty btree root - repair unimplemented");
+			ret = FSCK_ERR_EXIT;
+		}
 	}
-fsck_err:
+
 	return ret;
 }
 
-static int ptr_gens_check(struct bch_fs *c, enum bkey_type type,
-			  struct bkey_s_c k)
+static int bch2_check_fix_ptrs(struct bch_fs *c, enum btree_id btree_id,
+			       unsigned level, bool is_root,
+			       struct bkey_s_c *k)
 {
-	const struct bch_extent_ptr *ptr;
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(*k);
+	const union bch_extent_entry *entry;
+	struct extent_ptr_decoded p = { 0 };
+	bool do_update = false;
 	int ret = 0;
 
-	switch (type) {
-	case BKEY_TYPE_BTREE:
-	case BKEY_TYPE_EXTENTS:
-		switch (k.k->type) {
-		case BCH_EXTENT:
-		case BCH_EXTENT_CACHED: {
-			struct bkey_s_c_extent e = bkey_s_c_to_extent(k);
-
-			extent_for_each_ptr(e, ptr) {
-				ret = ptr_gen_check(c, type, ptr);
-				if (ret)
-					return ret;
+	bkey_for_each_ptr_decode(k->k, ptrs, p, entry) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, p.ptr.dev);
+		struct bucket *g = PTR_BUCKET(ca, &p.ptr, true);
+		struct bucket *g2 = PTR_BUCKET(ca, &p.ptr, false);
+
+		if (fsck_err_on(!g->gen_valid, c,
+				"bucket %u:%zu data type %s ptr gen %u missing in alloc btree",
+				p.ptr.dev, PTR_BUCKET_NR(ca, &p.ptr),
+				bch2_data_types[ptr_data_type(k->k, &p.ptr)],
+				p.ptr.gen)) {
+			if (!p.ptr.cached) {
+				g2->_mark.gen	= g->_mark.gen		= p.ptr.gen;
+				g2->gen_valid	= g->gen_valid		= true;
+				set_bit(BCH_FS_NEED_ALLOC_WRITE, &c->flags);
+			} else {
+				do_update = true;
+			}
+		}
 
+		if (fsck_err_on(gen_cmp(p.ptr.gen, g->mark.gen) > 0, c,
+				"bucket %u:%zu data type %s ptr gen in the future: %u > %u",
+				p.ptr.dev, PTR_BUCKET_NR(ca, &p.ptr),
+				bch2_data_types[ptr_data_type(k->k, &p.ptr)],
+				p.ptr.gen, g->mark.gen)) {
+			if (!p.ptr.cached) {
+				g2->_mark.gen	= g->_mark.gen	= p.ptr.gen;
+				g2->gen_valid	= g->gen_valid	= true;
+				g2->_mark.data_type		= 0;
+				g2->_mark.dirty_sectors		= 0;
+				g2->_mark.cached_sectors	= 0;
+				set_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags);
+				set_bit(BCH_FS_NEED_ALLOC_WRITE, &c->flags);
+			} else {
+				do_update = true;
 			}
-			break;
 		}
+
+		if (fsck_err_on(!p.ptr.cached &&
+				gen_cmp(p.ptr.gen, g->mark.gen) < 0, c,
+				"bucket %u:%zu data type %s stale dirty ptr: %u < %u",
+				p.ptr.dev, PTR_BUCKET_NR(ca, &p.ptr),
+				bch2_data_types[ptr_data_type(k->k, &p.ptr)],
+				p.ptr.gen, g->mark.gen))
+			do_update = true;
+
+		if (p.has_ec) {
+			struct stripe *m = genradix_ptr(&c->stripes[true], p.ec.idx);
+
+			if (fsck_err_on(!m || !m->alive, c,
+					"pointer to nonexistent stripe %llu",
+					(u64) p.ec.idx))
+				do_update = true;
+
+			if (fsck_err_on(!bch2_ptr_matches_stripe_m(m, p), c,
+					"pointer does not match stripe %llu",
+					(u64) p.ec.idx))
+				do_update = true;
 		}
-		break;
-	default:
-		break;
 	}
 
+	if (do_update) {
+		struct bkey_ptrs ptrs;
+		union bch_extent_entry *entry;
+		struct bch_extent_ptr *ptr;
+		struct bkey_i *new;
+
+		if (is_root) {
+			bch_err(c, "cannot update btree roots yet");
+			return -EINVAL;
+		}
+
+		new = kmalloc(bkey_bytes(k->k), GFP_KERNEL);
+		if (!new) {
+			bch_err(c, "%s: error allocating new key", __func__);
+			return -ENOMEM;
+		}
+
+		bkey_reassemble(new, *k);
+
+		if (level) {
+			/*
+			 * We don't want to drop btree node pointers - if the
+			 * btree node isn't there anymore, the read path will
+			 * sort it out:
+			 */
+			ptrs = bch2_bkey_ptrs(bkey_i_to_s(new));
+			bkey_for_each_ptr(ptrs, ptr) {
+				struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+				struct bucket *g = PTR_BUCKET(ca, ptr, true);
+
+				ptr->gen = g->mark.gen;
+			}
+		} else {
+			bch2_bkey_drop_ptrs(bkey_i_to_s(new), ptr, ({
+				struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+				struct bucket *g = PTR_BUCKET(ca, ptr, true);
+
+				(ptr->cached &&
+				 (!g->gen_valid || gen_cmp(ptr->gen, g->mark.gen) > 0)) ||
+				(!ptr->cached &&
+				 gen_cmp(ptr->gen, g->mark.gen) < 0);
+			}));
+again:
+			ptrs = bch2_bkey_ptrs(bkey_i_to_s(new));
+			bkey_extent_entry_for_each(ptrs, entry) {
+				if (extent_entry_type(entry) == BCH_EXTENT_ENTRY_stripe_ptr) {
+					struct stripe *m = genradix_ptr(&c->stripes[true],
+									entry->stripe_ptr.idx);
+					union bch_extent_entry *next_ptr;
+
+					bkey_extent_entry_for_each_from(ptrs, next_ptr, entry)
+						if (extent_entry_type(next_ptr) == BCH_EXTENT_ENTRY_ptr)
+							goto found;
+					next_ptr = NULL;
+found:
+					if (!next_ptr) {
+						bch_err(c, "aieee, found stripe ptr with no data ptr");
+						continue;
+					}
+
+					if (!m || !m->alive ||
+					    !__bch2_ptr_matches_stripe(&m->ptrs[entry->stripe_ptr.block],
+								       &next_ptr->ptr,
+								       m->sectors)) {
+						bch2_bkey_extent_entry_drop(new, entry);
+						goto again;
+					}
+				}
+			}
+		}
+
+		ret = bch2_journal_key_insert(c, btree_id, level, new);
+		if (ret)
+			kfree(new);
+		else
+			*k = bkey_i_to_s_c(new);
+	}
+fsck_err:
 	return ret;
 }
 
-/*
- * For runtime mark and sweep:
- */
-static int bch2_gc_mark_key(struct bch_fs *c, enum bkey_type type,
-			    struct bkey_s_c k, bool initial)
+/* marking of btree keys/nodes: */
+
+static int bch2_gc_mark_key(struct bch_fs *c, enum btree_id btree_id,
+			    unsigned level, bool is_root,
+			    struct bkey_s_c *k,
+			    u8 *max_stale, bool initial)
 {
-	struct gc_pos pos = { 0 };
+	struct bkey_ptrs_c ptrs;
+	const struct bch_extent_ptr *ptr;
 	unsigned flags =
-		BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-		BCH_BUCKET_MARK_GC_LOCK_HELD|
-		(initial ? BCH_BUCKET_MARK_NOATOMIC : 0);
+		BTREE_TRIGGER_GC|
+		(initial ? BTREE_TRIGGER_NOATOMIC : 0);
 	int ret = 0;
 
 	if (initial) {
-		BUG_ON(journal_seq_verify(c) &&
-		       k.k->version.lo > journal_cur_seq(&c->journal));
+		BUG_ON(bch2_journal_seq_verify &&
+		       k->k->version.lo > journal_cur_seq(&c->journal));
 
-		if (k.k->version.lo > atomic64_read(&c->key_version))
-			atomic64_set(&c->key_version, k.k->version.lo);
+		ret = bch2_check_fix_ptrs(c, btree_id, level, is_root, k);
+		if (ret)
+			goto err;
+
+		if (fsck_err_on(k->k->version.lo > atomic64_read(&c->key_version), c,
+				"key version number higher than recorded: %llu > %llu",
+				k->k->version.lo,
+				atomic64_read(&c->key_version)))
+			atomic64_set(&c->key_version, k->k->version.lo);
 
 		if (test_bit(BCH_FS_REBUILD_REPLICAS, &c->flags) ||
-		    fsck_err_on(!bch2_bkey_replicas_marked(c, type, k,
-							   false), c,
+		    fsck_err_on(!bch2_bkey_replicas_marked(c, *k), c,
 				"superblock not marked as containing replicas (type %u)",
-				type)) {
-			ret = bch2_mark_bkey_replicas(c, type, k);
-			if (ret)
-				return ret;
+				k->k->type)) {
+			ret = bch2_mark_bkey_replicas(c, *k);
+			if (ret) {
+				bch_err(c, "error marking bkey replicas: %i", ret);
+				goto err;
+			}
 		}
-
-		ret = ptr_gens_check(c, type, k);
-		if (ret)
-			return ret;
 	}
 
-	bch2_mark_key(c, type, k, true, k.k->size, pos, NULL, 0, flags);
+	ptrs = bch2_bkey_ptrs_c(*k);
+	bkey_for_each_ptr(ptrs, ptr) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+		struct bucket *g = PTR_BUCKET(ca, ptr, true);
+
+		if (gen_after(g->oldest_gen, ptr->gen))
+			g->oldest_gen = ptr->gen;
+
+		*max_stale = max(*max_stale, ptr_stale(ca, ptr));
+	}
 
-	ret = ptr_gens_recalc_oldest(c, type, k);
+	bch2_mark_key(c, *k, 0, k->k->size, NULL, 0, flags);
 fsck_err:
+err:
+	if (ret)
+		bch_err(c, "%s: ret %i", __func__, ret);
 	return ret;
 }
 
-static int btree_gc_mark_node(struct bch_fs *c, struct btree *b,
+static int btree_gc_mark_node(struct bch_fs *c, struct btree *b, u8 *max_stale,
 			      bool initial)
 {
-	enum bkey_type type = btree_node_type(b);
 	struct btree_node_iter iter;
 	struct bkey unpacked;
 	struct bkey_s_c k;
-	u8 stale = 0;
-	int ret;
+	struct bkey_buf prev, cur;
+	int ret = 0;
 
-	if (!bkey_type_needs_gc(type))
+	*max_stale = 0;
+
+	if (!btree_node_type_needs_gc(btree_node_type(b)))
 		return 0;
 
-	for_each_btree_node_key_unpack(b, k, &iter,
-				       &unpacked) {
-		bch2_bkey_debugcheck(c, b, k);
+	bch2_btree_node_iter_init_from_start(&iter, b);
+	bch2_bkey_buf_init(&prev);
+	bch2_bkey_buf_init(&cur);
+	bkey_init(&prev.k->k);
 
-		ret = bch2_gc_mark_key(c, type, k, initial);
-		if (ret < 0)
-			return ret;
+	while ((k = bch2_btree_node_iter_peek_unpack(&iter, b, &unpacked)).k) {
+		ret = bch2_gc_mark_key(c, b->c.btree_id, b->c.level, false,
+				       &k, max_stale, initial);
+		if (ret)
+			break;
+
+		bch2_btree_node_iter_advance(&iter, b);
 
-		stale = max_t(u8, stale, ret);
+		if (b->c.level) {
+			bch2_bkey_buf_reassemble(&cur, c, k);
+
+			ret = bch2_gc_check_topology(c, b, &prev, cur,
+					bch2_btree_node_iter_end(&iter));
+			if (ret)
+				break;
+		}
 	}
 
-	return stale;
+	bch2_bkey_buf_exit(&cur, c);
+	bch2_bkey_buf_exit(&prev, c);
+	return ret;
 }
 
 static int bch2_gc_btree(struct bch_fs *c, enum btree_id btree_id,
-			 bool initial)
+			 bool initial, bool metadata_only)
 {
-	struct btree_iter iter;
+	struct btree_trans trans;
+	struct btree_iter *iter;
 	struct btree *b;
-	struct range_checks r;
-	unsigned depth = bkey_type_needs_gc(btree_id) ? 0 : 1;
-	unsigned max_stale;
+	unsigned depth = metadata_only			? 1
+		: bch2_expensive_debug_checks		? 0
+		: !btree_node_type_needs_gc(btree_id)	? 1
+		: 0;
+	u8 max_stale = 0;
 	int ret = 0;
 
-	gc_pos_set(c, gc_pos_btree(btree_id, POS_MIN, 0));
-
-	if (!c->btree_roots[btree_id].b)
-		return 0;
-
-	/*
-	 * if expensive_debug_checks is on, run range_checks on all leaf nodes:
-	 *
-	 * and on startup, we have to read every btree node (XXX: only if it was
-	 * an unclean shutdown)
-	 */
-	if (initial || expensive_debug_checks(c))
-		depth = 0;
+	bch2_trans_init(&trans, c, 0, 0);
 
-	btree_node_range_checks_init(&r, depth);
+	gc_pos_set(c, gc_pos_btree(btree_id, POS_MIN, 0));
 
-	__for_each_btree_node(&iter, c, btree_id, POS_MIN,
+	__for_each_btree_node(&trans, iter, btree_id, POS_MIN,
 			      0, depth, BTREE_ITER_PREFETCH, b) {
-		btree_node_range_checks(c, b, &r);
-
 		bch2_verify_btree_nr_keys(b);
 
-		max_stale = btree_gc_mark_node(c, b, initial);
-
 		gc_pos_set(c, gc_pos_btree_node(b));
 
+		ret = btree_gc_mark_node(c, b, &max_stale, initial);
+		if (ret)
+			break;
+
 		if (!initial) {
 			if (max_stale > 64)
-				bch2_btree_node_rewrite(c, &iter,
+				bch2_btree_node_rewrite(c, iter,
 						b->data->keys.seq,
-						BTREE_INSERT_USE_RESERVE|
 						BTREE_INSERT_NOWAIT|
 						BTREE_INSERT_GC_LOCK_HELD);
-			else if (!btree_gc_rewrite_disabled(c) &&
-				 (btree_gc_always_rewrite(c) || max_stale > 16))
-				bch2_btree_node_rewrite(c, &iter,
+			else if (!bch2_btree_gc_rewrite_disabled &&
+				 (bch2_btree_gc_always_rewrite || max_stale > 16))
+				bch2_btree_node_rewrite(c, iter,
 						b->data->keys.seq,
 						BTREE_INSERT_NOWAIT|
 						BTREE_INSERT_GC_LOCK_HELD);
 		}
 
-		bch2_btree_iter_cond_resched(&iter);
+		bch2_trans_cond_resched(&trans);
 	}
-	ret = bch2_btree_iter_unlock(&iter);
+	bch2_trans_iter_put(&trans, iter);
+
+	ret = bch2_trans_exit(&trans) ?: ret;
 	if (ret)
 		return ret;
 
 	mutex_lock(&c->btree_root_lock);
-
 	b = c->btree_roots[btree_id].b;
-	if (!btree_node_fake(b))
-		bch2_gc_mark_key(c, BKEY_TYPE_BTREE,
-				 bkey_i_to_s_c(&b->key), initial);
-	gc_pos_set(c, gc_pos_btree_root(b->btree_id));
+	if (!btree_node_fake(b)) {
+		struct bkey_s_c k = bkey_i_to_s_c(&b->key);
 
+		ret = bch2_gc_mark_key(c, b->c.btree_id, b->c.level, true,
+				       &k, &max_stale, initial);
+	}
+	gc_pos_set(c, gc_pos_btree_root(b->c.btree_id));
 	mutex_unlock(&c->btree_root_lock);
-	return 0;
+
+	return ret;
 }
 
-static int bch2_gc_btrees(struct bch_fs *c, struct list_head *journal,
-			  bool initial)
+static int bch2_gc_btree_init_recurse(struct bch_fs *c, struct btree *b,
+				      unsigned target_depth)
 {
-	unsigned i;
+	struct btree_and_journal_iter iter;
+	struct bkey_s_c k;
+	struct bkey_buf cur, prev;
+	u8 max_stale = 0;
+	char buf[200];
+	int ret = 0;
 
-	for (i = 0; i < BTREE_ID_NR; i++) {
-		enum bkey_type type = bkey_type(0, i);
+	bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+	bch2_bkey_buf_init(&prev);
+	bch2_bkey_buf_init(&cur);
+	bkey_init(&prev.k->k);
 
-		int ret = bch2_gc_btree(c, i, initial);
-		if (ret)
-			return ret;
+	while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+		BUG_ON(bpos_cmp(k.k->p, b->data->min_key) < 0);
+		BUG_ON(bpos_cmp(k.k->p, b->data->max_key) > 0);
 
-		if (journal && bkey_type_needs_gc(type)) {
-			struct bkey_i *k, *n;
-			struct jset_entry *j;
-			struct journal_replay *r;
-			int ret;
-
-			list_for_each_entry(r, journal, list)
-				for_each_jset_key(k, n, j, &r->j) {
-					if (type == bkey_type(j->level, j->btree_id)) {
-						ret = bch2_gc_mark_key(c, type,
-							bkey_i_to_s_c(k), initial);
-						if (ret < 0)
-							return ret;
-					}
+		ret = bch2_gc_mark_key(c, b->c.btree_id, b->c.level, false,
+				       &k, &max_stale, true);
+		if (ret) {
+			bch_err(c, "%s: error %i from bch2_gc_mark_key", __func__, ret);
+			goto fsck_err;
+		}
+
+		if (b->c.level) {
+			bch2_bkey_buf_reassemble(&cur, c, k);
+			k = bkey_i_to_s_c(cur.k);
+
+			bch2_btree_and_journal_iter_advance(&iter);
+
+			ret = bch2_gc_check_topology(c, b,
+					&prev, cur,
+					!bch2_btree_and_journal_iter_peek(&iter).k);
+			if (ret)
+				goto fsck_err;
+		} else {
+			bch2_btree_and_journal_iter_advance(&iter);
+		}
+	}
+
+	if (b->c.level > target_depth) {
+		bch2_btree_and_journal_iter_exit(&iter);
+		bch2_btree_and_journal_iter_init_node_iter(&iter, c, b);
+
+		while ((k = bch2_btree_and_journal_iter_peek(&iter)).k) {
+			struct btree *child;
+
+			bch2_bkey_buf_reassemble(&cur, c, k);
+			bch2_btree_and_journal_iter_advance(&iter);
+
+			child = bch2_btree_node_get_noiter(c, cur.k,
+						b->c.btree_id, b->c.level - 1,
+						false);
+			ret = PTR_ERR_OR_ZERO(child);
+
+			if (ret == -EIO) {
+				bch2_topology_error(c);
+
+				if (fsck_err(c, "Unreadable btree node at btree %s level %u:\n"
+					"  %s",
+					bch2_btree_ids[b->c.btree_id],
+					b->c.level - 1,
+					(bch2_bkey_val_to_text(&PBUF(buf), c, bkey_i_to_s_c(cur.k)), buf))) {
+					ret = FSCK_ERR_START_TOPOLOGY_REPAIR;
+					bch_info(c, "Halting mark and sweep to start topology repair pass");
+					goto fsck_err;
+				} else {
+					/* Continue marking when opted to not
+					 * fix the error: */
+					ret = 0;
+					set_bit(BCH_FS_INITIAL_GC_UNFIXED, &c->flags);
+					continue;
 				}
+			} else if (ret) {
+				bch_err(c, "%s: error %i getting btree node",
+					__func__, ret);
+				break;
+			}
+
+			ret = bch2_gc_btree_init_recurse(c, child,
+							 target_depth);
+			six_unlock_read(&child->c.lock);
+
+			if (ret)
+				break;
 		}
 	}
+fsck_err:
+	bch2_bkey_buf_exit(&cur, c);
+	bch2_bkey_buf_exit(&prev, c);
+	bch2_btree_and_journal_iter_exit(&iter);
+	return ret;
+}
+
+static int bch2_gc_btree_init(struct bch_fs *c,
+			      enum btree_id btree_id,
+			      bool metadata_only)
+{
+	struct btree *b;
+	unsigned target_depth = metadata_only		? 1
+		: bch2_expensive_debug_checks		? 0
+		: !btree_node_type_needs_gc(btree_id)	? 1
+		: 0;
+	u8 max_stale = 0;
+	char buf[100];
+	int ret = 0;
+
+	b = c->btree_roots[btree_id].b;
+
+	if (btree_node_fake(b))
+		return 0;
+
+	six_lock_read(&b->c.lock, NULL, NULL);
+	if (mustfix_fsck_err_on(bpos_cmp(b->data->min_key, POS_MIN), c,
+			"btree root with incorrect min_key: %s",
+			(bch2_bpos_to_text(&PBUF(buf), b->data->min_key), buf))) {
+		bch_err(c, "repair unimplemented");
+		ret = FSCK_ERR_EXIT;
+		goto fsck_err;
+	}
 
-	return 0;
+	if (mustfix_fsck_err_on(bpos_cmp(b->data->max_key, POS_MAX), c,
+			"btree root with incorrect max_key: %s",
+			(bch2_bpos_to_text(&PBUF(buf), b->data->max_key), buf))) {
+		bch_err(c, "repair unimplemented");
+		ret = FSCK_ERR_EXIT;
+		goto fsck_err;
+	}
+
+	if (b->c.level >= target_depth)
+		ret = bch2_gc_btree_init_recurse(c, b, target_depth);
+
+	if (!ret) {
+		struct bkey_s_c k = bkey_i_to_s_c(&b->key);
+
+		ret = bch2_gc_mark_key(c, b->c.btree_id, b->c.level, true,
+				       &k, &max_stale, true);
+	}
+fsck_err:
+	six_unlock_read(&b->c.lock);
+
+	if (ret < 0)
+		bch_err(c, "%s: ret %i", __func__, ret);
+	return ret;
+}
+
+static inline int btree_id_gc_phase_cmp(enum btree_id l, enum btree_id r)
+{
+	return  (int) btree_id_to_gc_phase(l) -
+		(int) btree_id_to_gc_phase(r);
+}
+
+static int bch2_gc_btrees(struct bch_fs *c, bool initial, bool metadata_only)
+{
+	enum btree_id ids[BTREE_ID_NR];
+	unsigned i;
+	int ret = 0;
+
+	for (i = 0; i < BTREE_ID_NR; i++)
+		ids[i] = i;
+	bubble_sort(ids, BTREE_ID_NR, btree_id_gc_phase_cmp);
+
+	for (i = 0; i < BTREE_ID_NR && !ret; i++)
+		ret = initial
+			? bch2_gc_btree_init(c, ids[i], metadata_only)
+			: bch2_gc_btree(c, ids[i], initial, metadata_only);
+
+	if (ret < 0)
+		bch_err(c, "%s: ret %i", __func__, ret);
+	return ret;
 }
 
 static void mark_metadata_sectors(struct bch_fs *c, struct bch_dev *ca,
@@ -424,9 +937,7 @@ void bch2_mark_dev_superblock(struct bch_fs *c, struct bch_dev *ca,
 	 */
 	if (c) {
 		lockdep_assert_held(&c->sb_lock);
-		percpu_down_read_preempt_disable(&c->usage_lock);
-	} else {
-		preempt_disable();
+		percpu_down_read(&c->mark_lock);
 	}
 
 	for (i = 0; i < layout->nr_superblocks; i++) {
@@ -434,29 +945,22 @@ void bch2_mark_dev_superblock(struct bch_fs *c, struct bch_dev *ca,
 
 		if (offset == BCH_SB_SECTOR)
 			mark_metadata_sectors(c, ca, 0, BCH_SB_SECTOR,
-					      BCH_DATA_SB, flags);
+					      BCH_DATA_sb, flags);
 
 		mark_metadata_sectors(c, ca, offset,
 				      offset + (1 << layout->sb_max_size_bits),
-				      BCH_DATA_SB, flags);
+				      BCH_DATA_sb, flags);
 	}
 
-	if (c)
-		spin_lock(&c->journal.lock);
-
 	for (i = 0; i < ca->journal.nr; i++) {
 		b = ca->journal.buckets[i];
-		bch2_mark_metadata_bucket(c, ca, b, BCH_DATA_JOURNAL,
+		bch2_mark_metadata_bucket(c, ca, b, BCH_DATA_journal,
 					  ca->mi.bucket_size,
 					  gc_phase(GC_PHASE_SB), flags);
 	}
 
-	if (c) {
-		percpu_up_read_preempt_enable(&c->usage_lock);
-		spin_unlock(&c->journal.lock);
-	} else {
-		preempt_enable();
-	}
+	if (c)
+		percpu_up_read(&c->mark_lock);
 }
 
 static void bch2_mark_superblocks(struct bch_fs *c)
@@ -468,17 +972,14 @@ static void bch2_mark_superblocks(struct bch_fs *c)
 	gc_pos_set(c, gc_phase(GC_PHASE_SB));
 
 	for_each_online_member(ca, c, i)
-		bch2_mark_dev_superblock(c, ca,
-					 BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-					 BCH_BUCKET_MARK_GC_LOCK_HELD);
+		bch2_mark_dev_superblock(c, ca, BTREE_TRIGGER_GC);
 	mutex_unlock(&c->sb_lock);
 }
 
+#if 0
 /* Also see bch2_pending_btree_node_free_insert_done() */
 static void bch2_mark_pending_btree_node_frees(struct bch_fs *c)
 {
-	struct gc_pos pos = { 0 };
-	struct bch_fs_usage stats = { 0 };
 	struct btree_update *as;
 	struct pending_btree_node_free *d;
 
@@ -487,543 +988,535 @@ static void bch2_mark_pending_btree_node_frees(struct bch_fs *c)
 
 	for_each_pending_btree_node_free(c, as, d)
 		if (d->index_update_done)
-			bch2_mark_key(c, BKEY_TYPE_BTREE,
-				      bkey_i_to_s_c(&d->key),
-				      true, 0,
-				      pos, &stats, 0,
-				      BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-				      BCH_BUCKET_MARK_GC_LOCK_HELD);
-	/*
-	 * Don't apply stats - pending deletes aren't tracked in
-	 * bch_alloc_stats:
-	 */
+			bch2_mark_key(c, bkey_i_to_s_c(&d->key),
+				      0, 0, NULL, 0,
+				      BTREE_TRIGGER_GC);
 
 	mutex_unlock(&c->btree_interior_update_lock);
 }
+#endif
 
-static void bch2_mark_allocator_buckets(struct bch_fs *c)
+static void bch2_gc_free(struct bch_fs *c)
 {
 	struct bch_dev *ca;
-	struct open_bucket *ob;
-	size_t i, j, iter;
-	unsigned ci;
+	unsigned i;
 
-	percpu_down_read_preempt_disable(&c->usage_lock);
+	genradix_free(&c->stripes[1]);
 
-	spin_lock(&c->freelist_lock);
-	gc_pos_set(c, gc_pos_alloc(c, NULL));
+	for_each_member_device(ca, c, i) {
+		kvpfree(rcu_dereference_protected(ca->buckets[1], 1),
+			sizeof(struct bucket_array) +
+			ca->mi.nbuckets * sizeof(struct bucket));
+		ca->buckets[1] = NULL;
 
-	for_each_member_device(ca, c, ci) {
-		fifo_for_each_entry(i, &ca->free_inc, iter)
-			bch2_mark_alloc_bucket(c, ca, i, true,
-					       gc_pos_alloc(c, NULL),
-					       BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-					       BCH_BUCKET_MARK_GC_LOCK_HELD);
+		free_percpu(ca->usage_gc);
+		ca->usage_gc = NULL;
+	}
 
+	free_percpu(c->usage_gc);
+	c->usage_gc = NULL;
+}
 
+static int bch2_gc_done(struct bch_fs *c,
+			bool initial, bool metadata_only)
+{
+	struct bch_dev *ca = NULL;
+	bool verify = !metadata_only && (!initial ||
+		       (c->sb.compat & (1ULL << BCH_COMPAT_alloc_info)));
+	unsigned i, dev;
+	int ret = 0;
 
-		for (j = 0; j < RESERVE_NR; j++)
-			fifo_for_each_entry(i, &ca->free[j], iter)
-				bch2_mark_alloc_bucket(c, ca, i, true,
-						       gc_pos_alloc(c, NULL),
-						       BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-						       BCH_BUCKET_MARK_GC_LOCK_HELD);
+#define copy_field(_f, _msg, ...)					\
+	if (dst->_f != src->_f) {					\
+		if (verify)						\
+			fsck_err(c, _msg ": got %llu, should be %llu"	\
+				, ##__VA_ARGS__, dst->_f, src->_f);	\
+		dst->_f = src->_f;					\
+		set_bit(BCH_FS_NEED_ALLOC_WRITE, &c->flags);		\
+	}
+#define copy_stripe_field(_f, _msg, ...)				\
+	if (dst->_f != src->_f) {					\
+		if (verify)						\
+			fsck_err(c, "stripe %zu has wrong "_msg		\
+				": got %u, should be %u",		\
+				iter.pos, ##__VA_ARGS__,		\
+				dst->_f, src->_f);			\
+		dst->_f = src->_f;					\
+		set_bit(BCH_FS_NEED_ALLOC_WRITE, &c->flags);		\
 	}
+#define copy_bucket_field(_f)						\
+	if (dst->b[b].mark._f != src->b[b].mark._f) {			\
+		if (verify)						\
+			fsck_err(c, "bucket %u:%zu gen %u data type %s has wrong " #_f	\
+				": got %u, should be %u", dev, b,	\
+				dst->b[b].mark.gen,			\
+				bch2_data_types[dst->b[b].mark.data_type],\
+				dst->b[b].mark._f, src->b[b].mark._f);	\
+		dst->b[b]._mark._f = src->b[b].mark._f;			\
+		set_bit(BCH_FS_NEED_ALLOC_WRITE, &c->flags);		\
+	}
+#define copy_dev_field(_f, _msg, ...)					\
+	copy_field(_f, "dev %u has wrong " _msg, dev, ##__VA_ARGS__)
+#define copy_fs_field(_f, _msg, ...)					\
+	copy_field(_f, "fs has wrong " _msg, ##__VA_ARGS__)
+
+	if (!metadata_only) {
+		struct genradix_iter iter = genradix_iter_init(&c->stripes[1], 0);
+		struct stripe *dst, *src;
+
+		while ((src = genradix_iter_peek(&iter, &c->stripes[1]))) {
+			dst = genradix_ptr_alloc(&c->stripes[0], iter.pos, GFP_KERNEL);
+
+			if (dst->alive		!= src->alive ||
+			    dst->sectors	!= src->sectors ||
+			    dst->algorithm	!= src->algorithm ||
+			    dst->nr_blocks	!= src->nr_blocks ||
+			    dst->nr_redundant	!= src->nr_redundant) {
+				bch_err(c, "unexpected stripe inconsistency at bch2_gc_done, confused");
+				ret = -EINVAL;
+				goto fsck_err;
+			}
 
-	spin_unlock(&c->freelist_lock);
-
-	for (ob = c->open_buckets;
-	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets);
-	     ob++) {
-		spin_lock(&ob->lock);
-		if (ob->valid) {
-			gc_pos_set(c, gc_pos_alloc(c, ob));
-			ca = bch_dev_bkey_exists(c, ob->ptr.dev);
-			bch2_mark_alloc_bucket(c, ca, PTR_BUCKET_NR(ca, &ob->ptr), true,
-					       gc_pos_alloc(c, ob),
-					       BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
-					       BCH_BUCKET_MARK_GC_LOCK_HELD);
+			for (i = 0; i < ARRAY_SIZE(dst->block_sectors); i++)
+				copy_stripe_field(block_sectors[i],
+						  "block_sectors[%u]", i);
+
+			dst->blocks_nonempty = 0;
+			for (i = 0; i < dst->nr_blocks; i++)
+				dst->blocks_nonempty += dst->block_sectors[i] != 0;
+
+			genradix_iter_advance(&iter, &c->stripes[1]);
 		}
-		spin_unlock(&ob->lock);
 	}
 
-	percpu_up_read_preempt_enable(&c->usage_lock);
-}
+	for (i = 0; i < ARRAY_SIZE(c->usage); i++)
+		bch2_fs_usage_acc_to_base(c, i);
 
-static void bch2_gc_start(struct bch_fs *c)
-{
-	struct bch_dev *ca;
-	struct bucket_array *buckets;
-	struct bucket_mark new;
-	unsigned i;
-	size_t b;
-	int cpu;
+	for_each_member_device(ca, c, dev) {
+		struct bucket_array *dst = __bucket_array(ca, 0);
+		struct bucket_array *src = __bucket_array(ca, 1);
+		size_t b;
 
-	percpu_down_write(&c->usage_lock);
+		for (b = 0; b < src->nbuckets; b++) {
+			copy_bucket_field(gen);
+			copy_bucket_field(data_type);
+			copy_bucket_field(stripe);
+			copy_bucket_field(dirty_sectors);
+			copy_bucket_field(cached_sectors);
 
-	/*
-	 * Indicates to buckets code that gc is now in progress - done under
-	 * usage_lock to avoid racing with bch2_mark_key():
-	 */
-	__gc_pos_set(c, gc_phase(GC_PHASE_START));
-
-	/* Save a copy of the existing bucket stats while we recompute them: */
-	for_each_member_device(ca, c, i) {
-		ca->usage_cached = __bch2_dev_usage_read(ca);
-		for_each_possible_cpu(cpu) {
-			struct bch_dev_usage *p =
-				per_cpu_ptr(ca->usage_percpu, cpu);
-			memset(p, 0, sizeof(*p));
+			dst->b[b].oldest_gen = src->b[b].oldest_gen;
 		}
-	}
 
-	c->usage_cached = __bch2_fs_usage_read(c);
-	for_each_possible_cpu(cpu) {
-		struct bch_fs_usage *p =
-			per_cpu_ptr(c->usage_percpu, cpu);
+		{
+			struct bch_dev_usage *dst = ca->usage_base;
+			struct bch_dev_usage *src = (void *)
+				bch2_acc_percpu_u64s((void *) ca->usage_gc,
+						     dev_usage_u64s());
 
-		memset(p->replicas, 0, sizeof(p->replicas));
-		memset(p->buckets, 0, sizeof(p->buckets));
-	}
+			copy_dev_field(buckets_ec,		"buckets_ec");
+			copy_dev_field(buckets_unavailable,	"buckets_unavailable");
 
-	percpu_up_write(&c->usage_lock);
+			for (i = 0; i < BCH_DATA_NR; i++) {
+				copy_dev_field(d[i].buckets,	"%s buckets", bch2_data_types[i]);
+				copy_dev_field(d[i].sectors,	"%s sectors", bch2_data_types[i]);
+				copy_dev_field(d[i].fragmented,	"%s fragmented", bch2_data_types[i]);
+			}
+		}
+	};
+
+	{
+		unsigned nr = fs_usage_u64s(c);
+		struct bch_fs_usage *dst = c->usage_base;
+		struct bch_fs_usage *src = (void *)
+			bch2_acc_percpu_u64s((void *) c->usage_gc, nr);
+
+		copy_fs_field(hidden,		"hidden");
+		copy_fs_field(btree,		"btree");
+
+		if (!metadata_only) {
+			copy_fs_field(data,	"data");
+			copy_fs_field(cached,	"cached");
+			copy_fs_field(reserved,	"reserved");
+			copy_fs_field(nr_inodes,"nr_inodes");
+
+			for (i = 0; i < BCH_REPLICAS_MAX; i++)
+				copy_fs_field(persistent_reserved[i],
+					      "persistent_reserved[%i]", i);
+		}
 
-	/* Clear bucket marks: */
-	for_each_member_device(ca, c, i) {
-		down_read(&ca->bucket_lock);
-		buckets = bucket_array(ca);
+		for (i = 0; i < c->replicas.nr; i++) {
+			struct bch_replicas_entry *e =
+				cpu_replicas_entry(&c->replicas, i);
+			char buf[80];
 
-		for (b = buckets->first_bucket; b < buckets->nbuckets; b++) {
-			bucket_cmpxchg(buckets->b + b, new, ({
-				new.owned_by_allocator	= 0;
-				new.data_type		= 0;
-				new.cached_sectors	= 0;
-				new.dirty_sectors	= 0;
-			}));
-			ca->oldest_gens[b] = new.gen;
+			if (metadata_only &&
+			    (e->data_type == BCH_DATA_user ||
+			     e->data_type == BCH_DATA_cached))
+				continue;
+
+			bch2_replicas_entry_to_text(&PBUF(buf), e);
+
+			copy_fs_field(replicas[i], "%s", buf);
 		}
-		up_read(&ca->bucket_lock);
 	}
+
+#undef copy_fs_field
+#undef copy_dev_field
+#undef copy_bucket_field
+#undef copy_stripe_field
+#undef copy_field
+fsck_err:
+	if (ca)
+		percpu_ref_put(&ca->ref);
+	if (ret)
+		bch_err(c, "%s: ret %i", __func__, ret);
+	return ret;
 }
 
-/**
- * bch_gc - recompute bucket marks and oldest_gen, rewrite btree nodes
- */
-void bch2_gc(struct bch_fs *c)
+static int bch2_gc_start(struct bch_fs *c,
+			 bool metadata_only)
 {
-	struct bch_dev *ca;
-	u64 start_time = local_clock();
+	struct bch_dev *ca = NULL;
 	unsigned i;
 	int ret;
 
-	/*
-	 * Walk _all_ references to buckets, and recompute them:
-	 *
-	 * Order matters here:
-	 *  - Concurrent GC relies on the fact that we have a total ordering for
-	 *    everything that GC walks - see  gc_will_visit_node(),
-	 *    gc_will_visit_root()
-	 *
-	 *  - also, references move around in the course of index updates and
-	 *    various other crap: everything needs to agree on the ordering
-	 *    references are allowed to move around in - e.g., we're allowed to
-	 *    start with a reference owned by an open_bucket (the allocator) and
-	 *    move it to the btree, but not the reverse.
-	 *
-	 *    This is necessary to ensure that gc doesn't miss references that
-	 *    move around - if references move backwards in the ordering GC
-	 *    uses, GC could skip past them
-	 */
-	trace_gc_start(c);
+	BUG_ON(c->usage_gc);
 
-	/*
-	 * Do this before taking gc_lock - bch2_disk_reservation_get() blocks on
-	 * gc_lock if sectors_available goes to 0:
-	 */
-	bch2_recalc_sectors_available(c);
-
-	down_write(&c->gc_lock);
-	if (test_bit(BCH_FS_GC_FAILURE, &c->flags))
-		goto out;
+	c->usage_gc = __alloc_percpu_gfp(fs_usage_u64s(c) * sizeof(u64),
+					 sizeof(u64), GFP_KERNEL);
+	if (!c->usage_gc) {
+		bch_err(c, "error allocating c->usage_gc");
+		return -ENOMEM;
+	}
 
-	bch2_gc_start(c);
+	for_each_member_device(ca, c, i) {
+		BUG_ON(ca->buckets[1]);
+		BUG_ON(ca->usage_gc);
+
+		ca->buckets[1] = kvpmalloc(sizeof(struct bucket_array) +
+				ca->mi.nbuckets * sizeof(struct bucket),
+				GFP_KERNEL|__GFP_ZERO);
+		if (!ca->buckets[1]) {
+			percpu_ref_put(&ca->ref);
+			bch_err(c, "error allocating ca->buckets[gc]");
+			return -ENOMEM;
+		}
 
-	bch2_mark_superblocks(c);
+		ca->usage_gc = alloc_percpu(struct bch_dev_usage);
+		if (!ca->usage_gc) {
+			bch_err(c, "error allocating ca->usage_gc");
+			percpu_ref_put(&ca->ref);
+			return -ENOMEM;
+		}
+	}
 
-	ret = bch2_gc_btrees(c, NULL, false);
+	ret = bch2_ec_mem_alloc(c, true);
 	if (ret) {
-		bch_err(c, "btree gc failed: %d", ret);
-		set_bit(BCH_FS_GC_FAILURE, &c->flags);
-		goto out;
+		bch_err(c, "error allocating ec gc mem");
+		return ret;
 	}
 
-	bch2_mark_pending_btree_node_frees(c);
-	bch2_mark_allocator_buckets(c);
-
-	/* Indicates that gc is no longer in progress: */
-	gc_pos_set(c, gc_phase(GC_PHASE_DONE));
-	c->gc_count++;
-out:
-	up_write(&c->gc_lock);
-	trace_gc_end(c);
-	bch2_time_stats_update(&c->times[BCH_TIME_btree_gc], start_time);
+	percpu_down_write(&c->mark_lock);
 
 	/*
-	 * Wake up allocator in case it was waiting for buckets
-	 * because of not being able to inc gens
+	 * indicate to stripe code that we need to allocate for the gc stripes
+	 * radix tree, too
 	 */
-	for_each_member_device(ca, c, i)
-		bch2_wake_allocator(ca);
+	gc_pos_set(c, gc_phase(GC_PHASE_START));
 
-	/*
-	 * At startup, allocations can happen directly instead of via the
-	 * allocator thread - issue wakeup in case they blocked on gc_lock:
-	 */
-	closure_wake_up(&c->freelist_wait);
-}
+	for_each_member_device(ca, c, i) {
+		struct bucket_array *dst = __bucket_array(ca, 1);
+		struct bucket_array *src = __bucket_array(ca, 0);
+		size_t b;
 
-/* Btree coalescing */
+		dst->first_bucket	= src->first_bucket;
+		dst->nbuckets		= src->nbuckets;
 
-static void recalc_packed_keys(struct btree *b)
-{
-	struct bset *i = btree_bset_first(b);
-	struct bkey_packed *k;
+		for (b = 0; b < src->nbuckets; b++) {
+			struct bucket *d = &dst->b[b];
+			struct bucket *s = &src->b[b];
 
-	memset(&b->nr, 0, sizeof(b->nr));
+			d->_mark.gen = dst->b[b].oldest_gen = s->mark.gen;
+			d->gen_valid = s->gen_valid;
 
-	BUG_ON(b->nsets != 1);
+			if (metadata_only &&
+			    (s->mark.data_type == BCH_DATA_user ||
+			     s->mark.data_type == BCH_DATA_cached))
+				d->_mark = s->mark;
+		}
+	};
 
-	vstruct_for_each(i, k)
-		btree_keys_account_key_add(&b->nr, 0, k);
+	percpu_up_write(&c->mark_lock);
+
+	return 0;
 }
 
-static void bch2_coalesce_nodes(struct bch_fs *c, struct btree_iter *iter,
-				struct btree *old_nodes[GC_MERGE_NODES])
+/**
+ * bch2_gc - walk _all_ references to buckets, and recompute them:
+ *
+ * Order matters here:
+ *  - Concurrent GC relies on the fact that we have a total ordering for
+ *    everything that GC walks - see  gc_will_visit_node(),
+ *    gc_will_visit_root()
+ *
+ *  - also, references move around in the course of index updates and
+ *    various other crap: everything needs to agree on the ordering
+ *    references are allowed to move around in - e.g., we're allowed to
+ *    start with a reference owned by an open_bucket (the allocator) and
+ *    move it to the btree, but not the reverse.
+ *
+ *    This is necessary to ensure that gc doesn't miss references that
+ *    move around - if references move backwards in the ordering GC
+ *    uses, GC could skip past them
+ */
+int bch2_gc(struct bch_fs *c, bool initial, bool metadata_only)
 {
-	struct btree *parent = btree_node_parent(iter, old_nodes[0]);
-	unsigned i, nr_old_nodes, nr_new_nodes, u64s = 0;
-	unsigned blocks = btree_blocks(c) * 2 / 3;
-	struct btree *new_nodes[GC_MERGE_NODES];
-	struct btree_update *as;
-	struct keylist keylist;
-	struct bkey_format_state format_state;
-	struct bkey_format new_format;
-
-	memset(new_nodes, 0, sizeof(new_nodes));
-	bch2_keylist_init(&keylist, NULL);
-
-	/* Count keys that are not deleted */
-	for (i = 0; i < GC_MERGE_NODES && old_nodes[i]; i++)
-		u64s += old_nodes[i]->nr.live_u64s;
-
-	nr_old_nodes = nr_new_nodes = i;
-
-	/* Check if all keys in @old_nodes could fit in one fewer node */
-	if (nr_old_nodes <= 1 ||
-	    __vstruct_blocks(struct btree_node, c->block_bits,
-			     DIV_ROUND_UP(u64s, nr_old_nodes - 1)) > blocks)
-		return;
+	struct bch_dev *ca;
+	u64 start_time = local_clock();
+	unsigned i, iter = 0;
+	int ret;
 
-	/* Find a format that all keys in @old_nodes can pack into */
-	bch2_bkey_format_init(&format_state);
+	lockdep_assert_held(&c->state_lock);
+	trace_gc_start(c);
 
-	for (i = 0; i < nr_old_nodes; i++)
-		__bch2_btree_calc_format(&format_state, old_nodes[i]);
+	down_write(&c->gc_lock);
 
-	new_format = bch2_bkey_format_done(&format_state);
+	/* flush interior btree updates: */
+	closure_wait_event(&c->btree_interior_update_wait,
+			   !bch2_btree_interior_updates_nr_pending(c));
+again:
+	ret = bch2_gc_start(c, metadata_only);
+	if (ret)
+		goto out;
 
-	/* Check if repacking would make any nodes too big to fit */
-	for (i = 0; i < nr_old_nodes; i++)
-		if (!bch2_btree_node_format_fits(c, old_nodes[i], &new_format)) {
-			trace_btree_gc_coalesce_fail(c,
-					BTREE_GC_COALESCE_FAIL_FORMAT_FITS);
-			return;
-		}
+	bch2_mark_superblocks(c);
 
-	if (bch2_keylist_realloc(&keylist, NULL, 0,
-			(BKEY_U64s + BKEY_EXTENT_U64s_MAX) * nr_old_nodes)) {
-		trace_btree_gc_coalesce_fail(c,
-				BTREE_GC_COALESCE_FAIL_KEYLIST_REALLOC);
-		return;
+	if (test_bit(BCH_FS_TOPOLOGY_ERROR, &c->flags) &&
+	    !test_bit(BCH_FS_INITIAL_GC_DONE, &c->flags) &&
+	    c->opts.fix_errors != FSCK_OPT_NO) {
+		bch_info(c, "starting topology repair pass");
+		ret = bch2_repair_topology(c);
+		if (ret)
+			goto out;
+		bch_info(c, "topology repair pass done");
 	}
 
-	as = bch2_btree_update_start(c, iter->btree_id,
-			btree_update_reserve_required(c, parent) + nr_old_nodes,
-			BTREE_INSERT_NOFAIL|
-			BTREE_INSERT_USE_RESERVE,
-			NULL);
-	if (IS_ERR(as)) {
-		trace_btree_gc_coalesce_fail(c,
-				BTREE_GC_COALESCE_FAIL_RESERVE_GET);
-		bch2_keylist_free(&keylist, NULL);
-		return;
+	ret = bch2_gc_btrees(c, initial, metadata_only);
+
+	if (ret == FSCK_ERR_START_TOPOLOGY_REPAIR &&
+	    !test_bit(BCH_FS_INITIAL_GC_DONE, &c->flags)) {
+		set_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags);
+		ret = 0;
 	}
 
-	trace_btree_gc_coalesce(c, old_nodes[0]);
+	if (ret == FSCK_ERR_START_TOPOLOGY_REPAIR)
+		ret = FSCK_ERR_EXIT;
 
-	for (i = 0; i < nr_old_nodes; i++)
-		bch2_btree_interior_update_will_free_node(as, old_nodes[i]);
+	if (ret)
+		goto out;
 
-	/* Repack everything with @new_format and sort down to one bset */
-	for (i = 0; i < nr_old_nodes; i++)
-		new_nodes[i] =
-			__bch2_btree_node_alloc_replacement(as, old_nodes[i],
-							    new_format);
+#if 0
+	bch2_mark_pending_btree_node_frees(c);
+#endif
+	c->gc_count++;
 
-	/*
-	 * Conceptually we concatenate the nodes together and slice them
-	 * up at different boundaries.
-	 */
-	for (i = nr_new_nodes - 1; i > 0; --i) {
-		struct btree *n1 = new_nodes[i];
-		struct btree *n2 = new_nodes[i - 1];
-
-		struct bset *s1 = btree_bset_first(n1);
-		struct bset *s2 = btree_bset_first(n2);
-		struct bkey_packed *k, *last = NULL;
-
-		/* Calculate how many keys from @n2 we could fit inside @n1 */
-		u64s = 0;
-
-		for (k = s2->start;
-		     k < vstruct_last(s2) &&
-		     vstruct_blocks_plus(n1->data, c->block_bits,
-					 u64s + k->u64s) <= blocks;
-		     k = bkey_next(k)) {
-			last = k;
-			u64s += k->u64s;
+	if (test_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags) ||
+	    (!iter && bch2_test_restart_gc)) {
+		/*
+		 * XXX: make sure gens we fixed got saved
+		 */
+		if (iter++ <= 2) {
+			bch_info(c, "Second GC pass needed, restarting:");
+			clear_bit(BCH_FS_NEED_ANOTHER_GC, &c->flags);
+			__gc_pos_set(c, gc_phase(GC_PHASE_NOT_RUNNING));
+
+			percpu_down_write(&c->mark_lock);
+			bch2_gc_free(c);
+			percpu_up_write(&c->mark_lock);
+			/* flush fsck errors, reset counters */
+			bch2_flush_fsck_errs(c);
+
+			goto again;
 		}
 
-		if (u64s == le16_to_cpu(s2->u64s)) {
-			/* n2 fits entirely in n1 */
-			n1->key.k.p = n1->data->max_key = n2->data->max_key;
-
-			memcpy_u64s(vstruct_last(s1),
-				    s2->start,
-				    le16_to_cpu(s2->u64s));
-			le16_add_cpu(&s1->u64s, le16_to_cpu(s2->u64s));
-
-			set_btree_bset_end(n1, n1->set);
-
-			six_unlock_write(&n2->lock);
-			bch2_btree_node_free_never_inserted(c, n2);
-			six_unlock_intent(&n2->lock);
-
-			memmove(new_nodes + i - 1,
-				new_nodes + i,
-				sizeof(new_nodes[0]) * (nr_new_nodes - i));
-			new_nodes[--nr_new_nodes] = NULL;
-		} else if (u64s) {
-			/* move part of n2 into n1 */
-			n1->key.k.p = n1->data->max_key =
-				bkey_unpack_pos(n1, last);
-
-			n2->data->min_key =
-				btree_type_successor(iter->btree_id,
-						     n1->data->max_key);
-
-			memcpy_u64s(vstruct_last(s1),
-				    s2->start, u64s);
-			le16_add_cpu(&s1->u64s, u64s);
-
-			memmove(s2->start,
-				vstruct_idx(s2, u64s),
-				(le16_to_cpu(s2->u64s) - u64s) * sizeof(u64));
-			s2->u64s = cpu_to_le16(le16_to_cpu(s2->u64s) - u64s);
-
-			set_btree_bset_end(n1, n1->set);
-			set_btree_bset_end(n2, n2->set);
-		}
+		bch_info(c, "Unable to fix bucket gens, looping");
+		ret = -EINVAL;
+	}
+out:
+	if (!ret) {
+		bch2_journal_block(&c->journal);
+
+		percpu_down_write(&c->mark_lock);
+		ret = bch2_gc_done(c, initial, metadata_only);
+
+		bch2_journal_unblock(&c->journal);
+	} else {
+		percpu_down_write(&c->mark_lock);
 	}
 
-	for (i = 0; i < nr_new_nodes; i++) {
-		struct btree *n = new_nodes[i];
+	/* Indicates that gc is no longer in progress: */
+	__gc_pos_set(c, gc_phase(GC_PHASE_NOT_RUNNING));
 
-		recalc_packed_keys(n);
-		btree_node_reset_sib_u64s(n);
+	bch2_gc_free(c);
+	percpu_up_write(&c->mark_lock);
 
-		bch2_btree_build_aux_trees(n);
-		six_unlock_write(&n->lock);
+	up_write(&c->gc_lock);
 
-		bch2_btree_node_write(c, n, SIX_LOCK_intent);
-	}
+	trace_gc_end(c);
+	bch2_time_stats_update(&c->times[BCH_TIME_btree_gc], start_time);
 
 	/*
-	 * The keys for the old nodes get deleted. We don't want to insert keys
-	 * that compare equal to the keys for the new nodes we'll also be
-	 * inserting - we can't because keys on a keylist must be strictly
-	 * greater than the previous keys, and we also don't need to since the
-	 * key for the new node will serve the same purpose (overwriting the key
-	 * for the old node).
+	 * Wake up allocator in case it was waiting for buckets
+	 * because of not being able to inc gens
 	 */
-	for (i = 0; i < nr_old_nodes; i++) {
-		struct bkey_i delete;
-		unsigned j;
-
-		for (j = 0; j < nr_new_nodes; j++)
-			if (!bkey_cmp(old_nodes[i]->key.k.p,
-				      new_nodes[j]->key.k.p))
-				goto next;
-
-		bkey_init(&delete.k);
-		delete.k.p = old_nodes[i]->key.k.p;
-		bch2_keylist_add_in_order(&keylist, &delete);
-next:
-		i = i;
-	}
+	for_each_member_device(ca, c, i)
+		bch2_wake_allocator(ca);
 
 	/*
-	 * Keys for the new nodes get inserted: bch2_btree_insert_keys() only
-	 * does the lookup once and thus expects the keys to be in sorted order
-	 * so we have to make sure the new keys are correctly ordered with
-	 * respect to the deleted keys added in the previous loop
+	 * At startup, allocations can happen directly instead of via the
+	 * allocator thread - issue wakeup in case they blocked on gc_lock:
 	 */
-	for (i = 0; i < nr_new_nodes; i++)
-		bch2_keylist_add_in_order(&keylist, &new_nodes[i]->key);
-
-	/* Insert the newly coalesced nodes */
-	bch2_btree_insert_node(as, parent, iter, &keylist, 0);
-
-	BUG_ON(!bch2_keylist_empty(&keylist));
+	closure_wake_up(&c->freelist_wait);
+	return ret;
+}
 
-	BUG_ON(iter->l[old_nodes[0]->level].b != old_nodes[0]);
+static bool gc_btree_gens_key(struct bch_fs *c, struct bkey_s_c k)
+{
+	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
+	const struct bch_extent_ptr *ptr;
 
-	bch2_btree_iter_node_replace(iter, new_nodes[0]);
+	percpu_down_read(&c->mark_lock);
+	bkey_for_each_ptr(ptrs, ptr) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+		struct bucket *g = PTR_BUCKET(ca, ptr, false);
 
-	for (i = 0; i < nr_new_nodes; i++)
-		bch2_open_buckets_put(c, &new_nodes[i]->ob);
+		if (gen_after(g->mark.gen, ptr->gen) > 16) {
+			percpu_up_read(&c->mark_lock);
+			return true;
+		}
+	}
 
-	/* Free the old nodes and update our sliding window */
-	for (i = 0; i < nr_old_nodes; i++) {
-		bch2_btree_node_free_inmem(c, old_nodes[i], iter);
-		six_unlock_intent(&old_nodes[i]->lock);
+	bkey_for_each_ptr(ptrs, ptr) {
+		struct bch_dev *ca = bch_dev_bkey_exists(c, ptr->dev);
+		struct bucket *g = PTR_BUCKET(ca, ptr, false);
 
-		/*
-		 * the index update might have triggered a split, in which case
-		 * the nodes we coalesced - the new nodes we just created -
-		 * might not be sibling nodes anymore - don't add them to the
-		 * sliding window (except the first):
-		 */
-		if (!i) {
-			old_nodes[i] = new_nodes[i];
-		} else {
-			old_nodes[i] = NULL;
-			if (new_nodes[i])
-				six_unlock_intent(&new_nodes[i]->lock);
-		}
+		if (gen_after(g->gc_gen, ptr->gen))
+			g->gc_gen = ptr->gen;
 	}
+	percpu_up_read(&c->mark_lock);
 
-	bch2_btree_update_done(as);
-	bch2_keylist_free(&keylist, NULL);
+	return false;
 }
 
-static int bch2_coalesce_btree(struct bch_fs *c, enum btree_id btree_id)
+/*
+ * For recalculating oldest gen, we only need to walk keys in leaf nodes; btree
+ * node pointers currently never have cached pointers that can become stale:
+ */
+static int bch2_gc_btree_gens(struct bch_fs *c, enum btree_id btree_id)
 {
-	struct btree_iter iter;
-	struct btree *b;
-	bool kthread = (current->flags & PF_KTHREAD) != 0;
-	unsigned i;
+	struct btree_trans trans;
+	struct btree_iter *iter;
+	struct bkey_s_c k;
+	struct bkey_buf sk;
+	int ret = 0, commit_err = 0;
 
-	/* Sliding window of adjacent btree nodes */
-	struct btree *merge[GC_MERGE_NODES];
-	u32 lock_seq[GC_MERGE_NODES];
+	bch2_bkey_buf_init(&sk);
+	bch2_trans_init(&trans, c, 0, 0);
 
-	/*
-	 * XXX: We don't have a good way of positively matching on sibling nodes
-	 * that have the same parent - this code works by handling the cases
-	 * where they might not have the same parent, and is thus fragile. Ugh.
-	 *
-	 * Perhaps redo this to use multiple linked iterators?
-	 */
-	memset(merge, 0, sizeof(merge));
+	iter = bch2_trans_get_iter(&trans, btree_id, POS_MIN,
+				   BTREE_ITER_PREFETCH|
+				   BTREE_ITER_NOT_EXTENTS|
+				   BTREE_ITER_ALL_SNAPSHOTS);
 
-	__for_each_btree_node(&iter, c, btree_id, POS_MIN,
-			      BTREE_MAX_DEPTH, 0,
-			      BTREE_ITER_PREFETCH, b) {
-		memmove(merge + 1, merge,
-			sizeof(merge) - sizeof(merge[0]));
-		memmove(lock_seq + 1, lock_seq,
-			sizeof(lock_seq) - sizeof(lock_seq[0]));
+	while ((k = bch2_btree_iter_peek(iter)).k &&
+	       !(ret = bkey_err(k))) {
+		c->gc_gens_pos = iter->pos;
 
-		merge[0] = b;
+		if (gc_btree_gens_key(c, k) && !commit_err) {
+			bch2_bkey_buf_reassemble(&sk, c, k);
+			bch2_extent_normalize(c, bkey_i_to_s(sk.k));
 
-		for (i = 1; i < GC_MERGE_NODES; i++) {
-			if (!merge[i] ||
-			    !six_relock_intent(&merge[i]->lock, lock_seq[i]))
-				break;
+			bch2_trans_update(&trans, iter, sk.k, 0);
 
-			if (merge[i]->level != merge[0]->level) {
-				six_unlock_intent(&merge[i]->lock);
-				break;
+			commit_err = bch2_trans_commit(&trans, NULL, NULL,
+						       BTREE_INSERT_NOWAIT|
+						       BTREE_INSERT_NOFAIL);
+			if (commit_err == -EINTR) {
+				commit_err = 0;
+				continue;
 			}
 		}
-		memset(merge + i, 0, (GC_MERGE_NODES - i) * sizeof(merge[0]));
 
-		bch2_coalesce_nodes(c, &iter, merge);
-
-		for (i = 1; i < GC_MERGE_NODES && merge[i]; i++) {
-			lock_seq[i] = merge[i]->lock.state.seq;
-			six_unlock_intent(&merge[i]->lock);
-		}
-
-		lock_seq[0] = merge[0]->lock.state.seq;
-
-		if (kthread && kthread_should_stop()) {
-			bch2_btree_iter_unlock(&iter);
-			return -ESHUTDOWN;
-		}
+		bch2_btree_iter_advance(iter);
+	}
+	bch2_trans_iter_put(&trans, iter);
 
-		bch2_btree_iter_cond_resched(&iter);
+	bch2_trans_exit(&trans);
+	bch2_bkey_buf_exit(&sk, c);
 
-		/*
-		 * If the parent node wasn't relocked, it might have been split
-		 * and the nodes in our sliding window might not have the same
-		 * parent anymore - blow away the sliding window:
-		 */
-		if (btree_iter_node(&iter, iter.level + 1) &&
-		    !btree_node_intent_locked(&iter, iter.level + 1))
-			memset(merge + 1, 0,
-			       (GC_MERGE_NODES - 1) * sizeof(merge[0]));
-	}
-	return bch2_btree_iter_unlock(&iter);
+	return ret;
 }
 
-/**
- * bch_coalesce - coalesce adjacent nodes with low occupancy
- */
-void bch2_coalesce(struct bch_fs *c)
+int bch2_gc_gens(struct bch_fs *c)
 {
-	enum btree_id id;
-
-	if (test_bit(BCH_FS_GC_FAILURE, &c->flags))
-		return;
+	struct bch_dev *ca;
+	struct bucket_array *buckets;
+	struct bucket *g;
+	unsigned i;
+	int ret;
 
+	/*
+	 * Ideally we would be using state_lock and not gc_lock here, but that
+	 * introduces a deadlock in the RO path - we currently take the state
+	 * lock at the start of going RO, thus the gc thread may get stuck:
+	 */
 	down_read(&c->gc_lock);
-	trace_gc_coalesce_start(c);
 
-	for (id = 0; id < BTREE_ID_NR; id++) {
-		int ret = c->btree_roots[id].b
-			? bch2_coalesce_btree(c, id)
-			: 0;
+	for_each_member_device(ca, c, i) {
+		down_read(&ca->bucket_lock);
+		buckets = bucket_array(ca);
 
-		if (ret) {
-			if (ret != -ESHUTDOWN)
-				bch_err(c, "btree coalescing failed: %d", ret);
-			set_bit(BCH_FS_GC_FAILURE, &c->flags);
-			return;
+		for_each_bucket(g, buckets)
+			g->gc_gen = g->mark.gen;
+		up_read(&ca->bucket_lock);
+	}
+
+	for (i = 0; i < BTREE_ID_NR; i++)
+		if ((1 << i) & BTREE_ID_HAS_PTRS) {
+			c->gc_gens_btree = i;
+			c->gc_gens_pos = POS_MIN;
+			ret = bch2_gc_btree_gens(c, i);
+			if (ret) {
+				bch_err(c, "error recalculating oldest_gen: %i", ret);
+				goto err;
+			}
 		}
+
+	for_each_member_device(ca, c, i) {
+		down_read(&ca->bucket_lock);
+		buckets = bucket_array(ca);
+
+		for_each_bucket(g, buckets)
+			g->oldest_gen = g->gc_gen;
+		up_read(&ca->bucket_lock);
 	}
 
-	trace_gc_coalesce_end(c);
+	c->gc_gens_btree	= 0;
+	c->gc_gens_pos		= POS_MIN;
+
+	c->gc_count++;
+err:
 	up_read(&c->gc_lock);
+	return ret;
 }
 
 static int bch2_gc_thread(void *arg)
 {
 	struct bch_fs *c = arg;
 	struct io_clock *clock = &c->io_clock[WRITE];
-	unsigned long last = atomic_long_read(&clock->now);
+	unsigned long last = atomic64_read(&clock->now);
 	unsigned last_kick = atomic_read(&c->kick_gc);
+	int ret;
 
 	set_freezable();
 
@@ -1042,7 +1535,7 @@ static int bch2_gc_thread(void *arg)
 			if (c->btree_gc_periodic) {
 				unsigned long next = last + c->capacity / 16;
 
-				if (atomic_long_read(&clock->now) >= next)
+				if (atomic64_read(&clock->now) >= next)
 					break;
 
 				bch2_io_clock_schedule_timeout(clock, next);
@@ -1054,10 +1547,19 @@ static int bch2_gc_thread(void *arg)
 		}
 		__set_current_state(TASK_RUNNING);
 
-		last = atomic_long_read(&clock->now);
+		last = atomic64_read(&clock->now);
 		last_kick = atomic_read(&c->kick_gc);
 
-		bch2_gc(c);
+		/*
+		 * Full gc is currently incompatible with btree key cache:
+		 */
+#if 0
+		ret = bch2_gc(c, false, false);
+#else
+		ret = bch2_gc_gens(c);
+#endif
+		if (ret < 0)
+			bch_err(c, "btree gc failed: %i", ret);
 
 		debug_check_no_locks_held();
 	}
@@ -1082,57 +1584,17 @@ int bch2_gc_thread_start(struct bch_fs *c)
 {
 	struct task_struct *p;
 
-	BUG_ON(c->gc_thread);
+	if (c->gc_thread)
+		return 0;
 
-	p = kthread_create(bch2_gc_thread, c, "bch_gc");
-	if (IS_ERR(p))
+	p = kthread_create(bch2_gc_thread, c, "bch-gc/%s", c->name);
+	if (IS_ERR(p)) {
+		bch_err(c, "error creating gc thread: %li", PTR_ERR(p));
 		return PTR_ERR(p);
+	}
 
 	get_task_struct(p);
 	c->gc_thread = p;
 	wake_up_process(p);
 	return 0;
 }
-
-/* Initial GC computes bucket marks during startup */
-
-int bch2_initial_gc(struct bch_fs *c, struct list_head *journal)
-{
-	unsigned iter = 0;
-	int ret = 0;
-
-	down_write(&c->gc_lock);
-again:
-	bch2_gc_start(c);
-
-	bch2_mark_superblocks(c);
-
-	ret = bch2_gc_btrees(c, journal, true);
-	if (ret)
-		goto err;
-
-	if (test_bit(BCH_FS_FIXED_GENS, &c->flags)) {
-		if (iter++ > 2) {
-			bch_info(c, "Unable to fix bucket gens, looping");
-			ret = -EINVAL;
-			goto err;
-		}
-
-		bch_info(c, "Fixed gens, restarting initial mark and sweep:");
-		clear_bit(BCH_FS_FIXED_GENS, &c->flags);
-		goto again;
-	}
-
-	/*
-	 * Skip past versions that might have possibly been used (as nonces),
-	 * but hadn't had their pointers written:
-	 */
-	if (c->sb.encryption_type)
-		atomic64_add(1 << 16, &c->key_version);
-
-	gc_pos_set(c, gc_phase(GC_PHASE_DONE));
-	set_bit(BCH_FS_INITIAL_GC_DONE, &c->flags);
-err:
-	up_write(&c->gc_lock);
-	return ret;
-}