X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=libbcachefs%2Fbtree_cache.c;h=8e2488a4b58d00a45f78a7c64a6c1e83f4b0ff59;hb=b5fd066153c40a70a29caa1ea7987723ab687763;hp=d3addd3a89647164cbd4f0a48e69154c585dfa97;hpb=0243e4d41c980d2cf8771836f9fa2b43b69d1e29;p=bcachefs-tools-debian

diff --git a/libbcachefs/btree_cache.c b/libbcachefs/btree_cache.c
index d3addd3..8e2488a 100644
--- a/libbcachefs/btree_cache.c
+++ b/libbcachefs/btree_cache.c
@@ -1,19 +1,23 @@
 // SPDX-License-Identifier: GPL-2.0
 
 #include "bcachefs.h"
+#include "bkey_buf.h"
 #include "btree_cache.h"
 #include "btree_io.h"
 #include "btree_iter.h"
 #include "btree_locking.h"
 #include "debug.h"
+#include "errcode.h"
+#include "error.h"
+#include "journal.h"
+#include "trace.h"
 
 #include <linux/prefetch.h>
 #include <linux/sched/mm.h>
-#include <trace/events/bcachefs.h>
 
-const char * const bch2_btree_ids[] = {
-#define x(kwd, val, name) name,
-	BCH_BTREE_IDS()
+const char * const bch2_btree_node_flags[] = {
+#define x(f)	#f,
+	BTREE_FLAGS()
 #undef x
 	NULL
 };
@@ -22,13 +26,15 @@ void bch2_recalc_btree_reserve(struct bch_fs *c)
 {
 	unsigned i, reserve = 16;
 
-	if (!c->btree_roots[0].b)
+	if (!c->btree_roots_known[0].b)
 		reserve += 8;
 
-	for (i = 0; i < BTREE_ID_NR; i++)
-		if (c->btree_roots[i].b)
-			reserve += min_t(unsigned, 1,
-					 c->btree_roots[i].b->c.level) * 8;
+	for (i = 0; i < btree_id_nr_alive(c); i++) {
+		struct btree_root *r = bch2_btree_id_root(c, i);
+
+		if (r->b)
+			reserve += min_t(unsigned, 1, r->b->c.level) * 8;
+	}
 
 	c->btree_cache.reserve = reserve;
 }
@@ -38,22 +44,34 @@ static inline unsigned btree_cache_can_free(struct btree_cache *bc)
 	return max_t(int, 0, bc->used - bc->reserve);
 }
 
-static void __btree_node_data_free(struct bch_fs *c, struct btree *b)
+static void btree_node_to_freedlist(struct btree_cache *bc, struct btree *b)
 {
-	EBUG_ON(btree_node_write_in_flight(b));
-
-	kvpfree(b->data, btree_bytes(c));
-	b->data = NULL;
-	bch2_btree_keys_free(b);
+	if (b->c.lock.readers)
+		list_move(&b->list, &bc->freed_pcpu);
+	else
+		list_move(&b->list, &bc->freed_nonpcpu);
 }
 
 static void btree_node_data_free(struct bch_fs *c, struct btree *b)
 {
 	struct btree_cache *bc = &c->btree_cache;
 
-	__btree_node_data_free(c, b);
+	EBUG_ON(btree_node_write_in_flight(b));
+
+	clear_btree_node_just_written(b);
+
+	kvpfree(b->data, btree_bytes(c));
+	b->data = NULL;
+#ifdef __KERNEL__
+	kvfree(b->aux_data);
+#else
+	munmap(b->aux_data, btree_aux_data_bytes(b));
+#endif
+	b->aux_data = NULL;
+
 	bc->used--;
-	list_move(&b->list, &bc->freed);
+
+	btree_node_to_freedlist(bc, b);
 }
 
 static int bch2_btree_cache_cmp_fn(struct rhashtable_compare_arg *arg,
@@ -72,55 +90,74 @@ static const struct rhashtable_params bch_btree_cache_params = {
 	.obj_cmpfn	= bch2_btree_cache_cmp_fn,
 };
 
-static int __btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)
+static int btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)
 {
 	BUG_ON(b->data || b->aux_data);
 
 	b->data = kvpmalloc(btree_bytes(c), gfp);
 	if (!b->data)
-		return -ENOMEM;
-
-	if (bch2_btree_keys_alloc(b, btree_page_order(c), gfp)) {
+		return -BCH_ERR_ENOMEM_btree_node_mem_alloc;
+#ifdef __KERNEL__
+	b->aux_data = kvmalloc(btree_aux_data_bytes(b), gfp);
+#else
+	b->aux_data = mmap(NULL, btree_aux_data_bytes(b),
+			   PROT_READ|PROT_WRITE|PROT_EXEC,
+			   MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
+	if (b->aux_data == MAP_FAILED)
+		b->aux_data = NULL;
+#endif
+	if (!b->aux_data) {
 		kvpfree(b->data, btree_bytes(c));
 		b->data = NULL;
-		return -ENOMEM;
+		return -BCH_ERR_ENOMEM_btree_node_mem_alloc;
 	}
 
 	return 0;
 }
 
-static void btree_node_data_alloc(struct bch_fs *c, struct btree *b, gfp_t gfp)
+static struct btree *__btree_node_mem_alloc(struct bch_fs *c, gfp_t gfp)
 {
-	struct btree_cache *bc = &c->btree_cache;
-
-	if (!__btree_node_data_alloc(c, b, gfp)) {
-		bc->used++;
-		list_move(&b->list, &bc->freeable);
-	} else {
-		list_move(&b->list, &bc->freed);
-	}
-}
+	struct btree *b;
 
-static struct btree *btree_node_mem_alloc(struct bch_fs *c, gfp_t gfp)
-{
-	struct btree *b = kzalloc(sizeof(struct btree), gfp);
+	b = kzalloc(sizeof(struct btree), gfp);
 	if (!b)
 		return NULL;
 
 	bkey_btree_ptr_init(&b->key);
-	six_lock_init(&b->c.lock);
 	INIT_LIST_HEAD(&b->list);
 	INIT_LIST_HEAD(&b->write_blocked);
+	b->byte_order = ilog2(btree_bytes(c));
+	return b;
+}
+
+struct btree *__bch2_btree_node_mem_alloc(struct bch_fs *c)
+{
+	struct btree_cache *bc = &c->btree_cache;
+	struct btree *b;
+
+	b = __btree_node_mem_alloc(c, GFP_KERNEL);
+	if (!b)
+		return NULL;
 
-	btree_node_data_alloc(c, b, gfp);
-	return b->data ? b : NULL;
+	if (btree_node_data_alloc(c, b, GFP_KERNEL)) {
+		kfree(b);
+		return NULL;
+	}
+
+	bch2_btree_lock_init(&b->c, 0);
+
+	bc->used++;
+	list_add(&b->list, &bc->freeable);
+	return b;
 }
 
 /* Btree in memory cache - hash table */
 
 void bch2_btree_node_hash_remove(struct btree_cache *bc, struct btree *b)
 {
-	rhashtable_remove_fast(&bc->table, &b->hash, bch_btree_cache_params);
+	int ret = rhashtable_remove_fast(&bc->table, &b->hash, bch_btree_cache_params);
+
+	BUG_ON(ret);
 
 	/* Cause future lookups for this node to fail: */
 	b->hash_val = 0;
@@ -146,7 +183,7 @@ int bch2_btree_node_hash_insert(struct btree_cache *bc, struct btree *b,
 	mutex_lock(&bc->lock);
 	ret = __bch2_btree_node_hash_insert(bc, b);
 	if (!ret)
-		list_add(&b->list, &bc->live);
+		list_add_tail(&b->list, &bc->live);
 	mutex_unlock(&bc->lock);
 
 	return ret;
@@ -171,55 +208,68 @@ static int __btree_node_reclaim(struct bch_fs *c, struct btree *b, bool flush)
 	int ret = 0;
 
 	lockdep_assert_held(&bc->lock);
+wait_on_io:
+	if (b->flags & ((1U << BTREE_NODE_dirty)|
+			(1U << BTREE_NODE_read_in_flight)|
+			(1U << BTREE_NODE_write_in_flight))) {
+		if (!flush)
+			return -BCH_ERR_ENOMEM_btree_node_reclaim;
+
+		/* XXX: waiting on IO with btree cache lock held */
+		bch2_btree_node_wait_on_read(b);
+		bch2_btree_node_wait_on_write(b);
+	}
 
 	if (!six_trylock_intent(&b->c.lock))
-		return -ENOMEM;
+		return -BCH_ERR_ENOMEM_btree_node_reclaim;
 
 	if (!six_trylock_write(&b->c.lock))
 		goto out_unlock_intent;
 
-	if (btree_node_noevict(b))
-		goto out_unlock;
-
-	if (!btree_node_may_write(b))
-		goto out_unlock;
+	/* recheck under lock */
+	if (b->flags & ((1U << BTREE_NODE_read_in_flight)|
+			(1U << BTREE_NODE_write_in_flight))) {
+		if (!flush)
+			goto out_unlock;
+		six_unlock_write(&b->c.lock);
+		six_unlock_intent(&b->c.lock);
+		goto wait_on_io;
+	}
 
-	if (btree_node_dirty(b) &&
-	    test_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags))
+	if (btree_node_noevict(b) ||
+	    btree_node_write_blocked(b) ||
+	    btree_node_will_make_reachable(b))
 		goto out_unlock;
 
-	if (btree_node_dirty(b) ||
-	    btree_node_write_in_flight(b) ||
-	    btree_node_read_in_flight(b)) {
+	if (btree_node_dirty(b)) {
 		if (!flush)
 			goto out_unlock;
-
-		wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
-			       TASK_UNINTERRUPTIBLE);
-
 		/*
 		 * Using the underscore version because we don't want to compact
 		 * bsets after the write, since this node is about to be evicted
 		 * - unless btree verify mode is enabled, since it runs out of
 		 * the post write cleanup:
 		 */
-		if (verify_btree_ondisk(c))
-			bch2_btree_node_write(c, b, SIX_LOCK_intent);
+		if (bch2_verify_btree_ondisk)
+			bch2_btree_node_write(c, b, SIX_LOCK_intent,
+					      BTREE_WRITE_cache_reclaim);
 		else
-			__bch2_btree_node_write(c, b, SIX_LOCK_read);
+			__bch2_btree_node_write(c, b,
+						BTREE_WRITE_cache_reclaim);
 
-		/* wait for any in flight btree write */
-		btree_node_wait_on_io(b);
+		six_unlock_write(&b->c.lock);
+		six_unlock_intent(&b->c.lock);
+		goto wait_on_io;
 	}
 out:
 	if (b->hash_val && !ret)
-		trace_btree_node_reap(c, b);
+		trace_and_count(c, btree_cache_reap, c, b);
 	return ret;
 out_unlock:
 	six_unlock_write(&b->c.lock);
 out_unlock_intent:
 	six_unlock_intent(&b->c.lock);
-	ret = -ENOMEM;
+	ret = -BCH_ERR_ENOMEM_btree_node_reclaim;
 	goto out;
 }
 
@@ -236,24 +286,23 @@ static int btree_node_write_and_reclaim(struct bch_fs *c, struct btree *b)
 static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
 					   struct shrink_control *sc)
 {
-	struct bch_fs *c = container_of(shrink, struct bch_fs,
-					btree_cache.shrink);
+	struct bch_fs *c = shrink->private_data;
 	struct btree_cache *bc = &c->btree_cache;
 	struct btree *b, *t;
 	unsigned long nr = sc->nr_to_scan;
-	unsigned long can_free;
-	unsigned long touched = 0;
+	unsigned long can_free = 0;
 	unsigned long freed = 0;
-	unsigned i;
+	unsigned long touched = 0;
+	unsigned i, flags;
+	unsigned long ret = SHRINK_STOP;
+	bool trigger_writes = atomic_read(&bc->dirty) + nr >=
+		bc->used * 3 / 4;
 
-	if (btree_shrinker_disabled(c))
+	if (bch2_btree_shrinker_disabled)
 		return SHRINK_STOP;
 
-	/* Return -1 if we can't do anything right now */
-	if (sc->gfp_mask & __GFP_FS)
-		mutex_lock(&bc->lock);
-	else if (!mutex_trylock(&bc->lock))
-		return -1;
+	mutex_lock(&bc->lock);
+	flags = memalloc_nofs_save();
 
 	/*
 	 * It's _really_ critical that we don't free too many btree nodes - we
@@ -262,19 +311,24 @@ static unsigned long bch2_btree_cache_scan(struct shrinker *shrink,
 	 * succeed, so that inserting keys into the btree can always succeed and
 	 * IO can always make forward progress:
 	 */
-	nr /= btree_pages(c);
 	can_free = btree_cache_can_free(bc);
 	nr = min_t(unsigned long, nr, can_free);
 
 	i = 0;
 	list_for_each_entry_safe(b, t, &bc->freeable, list) {
+		/*
+		 * Leave a few nodes on the freeable list, so that a btree split
+		 * won't have to hit the system allocator:
+		 */
+		if (++i <= 3)
+			continue;
+
 		touched++;
 
-		if (freed >= nr)
-			break;
+		if (touched >= nr)
+			goto out;
 
-		if (++i > 3 &&
-		    !btree_node_reclaim(c, b)) {
+		if (!btree_node_reclaim(c, b)) {
 			btree_node_data_free(c, b);
 			six_unlock_write(&b->c.lock);
 			six_unlock_intent(&b->c.lock);
@@ -285,78 +339,83 @@ restart:
 	list_for_each_entry_safe(b, t, &bc->live, list) {
 		touched++;
 
-		if (freed >= nr) {
-			/* Save position */
-			if (&t->list != &bc->live)
-				list_move_tail(&bc->live, &t->list);
-			break;
-		}
-
-		if (!btree_node_accessed(b) &&
-		    !btree_node_reclaim(c, b)) {
-			/* can't call bch2_btree_node_hash_remove under lock  */
+		if (btree_node_accessed(b)) {
+			clear_btree_node_accessed(b);
+		} else if (!btree_node_reclaim(c, b)) {
 			freed++;
-			if (&t->list != &bc->live)
-				list_move_tail(&bc->live, &t->list);
-
 			btree_node_data_free(c, b);
-			mutex_unlock(&bc->lock);
 
 			bch2_btree_node_hash_remove(bc, b);
 			six_unlock_write(&b->c.lock);
 			six_unlock_intent(&b->c.lock);
 
-			if (freed >= nr)
-				goto out;
-
-			if (sc->gfp_mask & __GFP_FS)
-				mutex_lock(&bc->lock);
-			else if (!mutex_trylock(&bc->lock))
-				goto out;
+			if (freed == nr)
+				goto out_rotate;
+		} else if (trigger_writes &&
+			   btree_node_dirty(b) &&
+			   !btree_node_will_make_reachable(b) &&
+			   !btree_node_write_blocked(b) &&
+			   six_trylock_read(&b->c.lock)) {
+			list_move(&bc->live, &b->list);
+			mutex_unlock(&bc->lock);
+			__bch2_btree_node_write(c, b, BTREE_WRITE_cache_reclaim);
+			six_unlock_read(&b->c.lock);
+			if (touched >= nr)
+				goto out_nounlock;
+			mutex_lock(&bc->lock);
 			goto restart;
-		} else
-			clear_btree_node_accessed(b);
-	}
+		}
 
-	mutex_unlock(&bc->lock);
+		if (touched >= nr)
+			break;
+	}
+out_rotate:
+	if (&t->list != &bc->live)
+		list_move_tail(&bc->live, &t->list);
 out:
-	return (unsigned long) freed * btree_pages(c);
+	mutex_unlock(&bc->lock);
+out_nounlock:
+	ret = freed;
+	memalloc_nofs_restore(flags);
+	trace_and_count(c, btree_cache_scan, sc->nr_to_scan, can_free, ret);
+	return ret;
 }
 
 static unsigned long bch2_btree_cache_count(struct shrinker *shrink,
 					    struct shrink_control *sc)
 {
-	struct bch_fs *c = container_of(shrink, struct bch_fs,
-					btree_cache.shrink);
+	struct bch_fs *c = shrink->private_data;
 	struct btree_cache *bc = &c->btree_cache;
 
-	if (btree_shrinker_disabled(c))
+	if (bch2_btree_shrinker_disabled)
 		return 0;
 
-	return btree_cache_can_free(bc) * btree_pages(c);
+	return btree_cache_can_free(bc);
 }
 
 void bch2_fs_btree_cache_exit(struct bch_fs *c)
 {
 	struct btree_cache *bc = &c->btree_cache;
 	struct btree *b;
-	unsigned i;
+	unsigned i, flags;
 
-	if (bc->shrink.list.next)
-		unregister_shrinker(&bc->shrink);
+	shrinker_free(bc->shrink);
 
+	/* vfree() can allocate memory: */
+	flags = memalloc_nofs_save();
 	mutex_lock(&bc->lock);
 
-#ifdef CONFIG_BCACHEFS_DEBUG
 	if (c->verify_data)
 		list_move(&c->verify_data->list, &bc->live);
 
 	kvpfree(c->verify_ondisk, btree_bytes(c));
-#endif
 
-	for (i = 0; i < BTREE_ID_NR; i++)
-		if (c->btree_roots[i].b)
-			list_add(&c->btree_roots[i].b->list, &bc->live);
+	for (i = 0; i < btree_id_nr_alive(c); i++) {
+		struct btree_root *r = bch2_btree_id_root(c, i);
+
+		if (r->b)
+			list_add(&r->b->list, &bc->live);
+	}
 
 	list_splice(&bc->freeable, &bc->live);
 
@@ -366,20 +425,23 @@ void bch2_fs_btree_cache_exit(struct bch_fs *c)
 		BUG_ON(btree_node_read_in_flight(b) ||
 		       btree_node_write_in_flight(b));
 
-		if (btree_node_dirty(b))
-			bch2_btree_complete_write(c, b, btree_current_write(b));
-		clear_btree_node_dirty(b);
-
 		btree_node_data_free(c, b);
 	}
 
-	while (!list_empty(&bc->freed)) {
-		b = list_first_entry(&bc->freed, struct btree, list);
+	BUG_ON(!bch2_journal_error(&c->journal) &&
+	       atomic_read(&c->btree_cache.dirty));
+
+	list_splice(&bc->freed_pcpu, &bc->freed_nonpcpu);
+
+	while (!list_empty(&bc->freed_nonpcpu)) {
+		b = list_first_entry(&bc->freed_nonpcpu, struct btree, list);
 		list_del(&b->list);
+		six_lock_exit(&b->c.lock);
 		kfree(b);
 	}
 
 	mutex_unlock(&bc->lock);
+	memalloc_nofs_restore(flags);
 
 	if (bc->table_init_done)
 		rhashtable_destroy(&bc->table);
@@ -388,53 +450,39 @@ void bch2_fs_btree_cache_exit(struct bch_fs *c)
 int bch2_fs_btree_cache_init(struct bch_fs *c)
 {
 	struct btree_cache *bc = &c->btree_cache;
+	struct shrinker *shrink;
 	unsigned i;
 	int ret = 0;
 
-	pr_verbose_init(c->opts, "");
-
 	ret = rhashtable_init(&bc->table, &bch_btree_cache_params);
 	if (ret)
-		goto out;
+		goto err;
 
 	bc->table_init_done = true;
 
 	bch2_recalc_btree_reserve(c);
 
 	for (i = 0; i < bc->reserve; i++)
-		if (!btree_node_mem_alloc(c, GFP_KERNEL)) {
-			ret = -ENOMEM;
-			goto out;
-		}
+		if (!__bch2_btree_node_mem_alloc(c))
+			goto err;
 
 	list_splice_init(&bc->live, &bc->freeable);
 
-#ifdef CONFIG_BCACHEFS_DEBUG
 	mutex_init(&c->verify_lock);
 
-	c->verify_ondisk = kvpmalloc(btree_bytes(c), GFP_KERNEL);
-	if (!c->verify_ondisk) {
-		ret = -ENOMEM;
-		goto out;
-	}
-
-	c->verify_data = btree_node_mem_alloc(c, GFP_KERNEL);
-	if (!c->verify_data) {
-		ret = -ENOMEM;
-		goto out;
-	}
-
-	list_del_init(&c->verify_data->list);
-#endif
+	shrink = shrinker_alloc(0, "%s-btree_cache", c->name);
+	if (!shrink)
+		goto err;
+	bc->shrink = shrink;
+	shrink->count_objects	= bch2_btree_cache_count;
+	shrink->scan_objects	= bch2_btree_cache_scan;
+	shrink->seeks		= 4;
+	shrink->private_data	= c;
+	shrinker_register(shrink);
 
-	bc->shrink.count_objects	= bch2_btree_cache_count;
-	bc->shrink.scan_objects		= bch2_btree_cache_scan;
-	bc->shrink.seeks		= 4;
-	bc->shrink.batch		= btree_pages(c) * 2;
-	register_shrinker(&bc->shrink);
-out:
-	pr_verbose_init(c->opts, "ret %i", ret);
-	return ret;
+	return 0;
+err:
+	return -BCH_ERR_ENOMEM_fs_btree_cache_init;
 }
 
 void bch2_fs_btree_cache_init_early(struct btree_cache *bc)
@@ -442,7 +490,8 @@ void bch2_fs_btree_cache_init_early(struct btree_cache *bc)
 	mutex_init(&bc->lock);
 	INIT_LIST_HEAD(&bc->live);
 	INIT_LIST_HEAD(&bc->freeable);
-	INIT_LIST_HEAD(&bc->freed);
+	INIT_LIST_HEAD(&bc->freed_pcpu);
+	INIT_LIST_HEAD(&bc->freed_nonpcpu);
 }
 
 /*
@@ -451,19 +500,21 @@ void bch2_fs_btree_cache_init_early(struct btree_cache *bc)
  * cannibalize_bucket() will take. This means every time we unlock the root of
  * the btree, we need to release this lock if we have it held.
  */
-void bch2_btree_cache_cannibalize_unlock(struct bch_fs *c)
+void bch2_btree_cache_cannibalize_unlock(struct btree_trans *trans)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
 
 	if (bc->alloc_lock == current) {
-		trace_btree_node_cannibalize_unlock(c);
+		trace_and_count(c, btree_cache_cannibalize_unlock, trans);
 		bc->alloc_lock = NULL;
 		closure_wake_up(&bc->alloc_wait);
 	}
 }
 
-int bch2_btree_cache_cannibalize_lock(struct bch_fs *c, struct closure *cl)
+int bch2_btree_cache_cannibalize_lock(struct btree_trans *trans, struct closure *cl)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
 	struct task_struct *old;
 
@@ -472,8 +523,8 @@ int bch2_btree_cache_cannibalize_lock(struct bch_fs *c, struct closure *cl)
 		goto success;
 
 	if (!cl) {
-		trace_btree_node_cannibalize_lock_fail(c);
-		return -ENOMEM;
+		trace_and_count(c, btree_cache_cannibalize_lock_fail, trans);
+		return -BCH_ERR_ENOMEM_btree_cache_cannibalize_lock;
 	}
 
 	closure_wait(&bc->alloc_wait, cl);
@@ -486,11 +537,11 @@ int bch2_btree_cache_cannibalize_lock(struct bch_fs *c, struct closure *cl)
 		goto success;
 	}
 
-	trace_btree_node_cannibalize_lock_fail(c);
-	return -EAGAIN;
+	trace_and_count(c, btree_cache_cannibalize_lock_fail, trans);
+	return -BCH_ERR_btree_cache_cannibalize_lock_blocked;
 
 success:
-	trace_btree_node_cannibalize_lock(c);
+	trace_and_count(c, btree_cache_cannibalize_lock, trans);
 	return 0;
 }
 
@@ -517,62 +568,75 @@ static struct btree *btree_node_cannibalize(struct bch_fs *c)
 	}
 }
 
-struct btree *bch2_btree_node_mem_alloc(struct bch_fs *c)
+struct btree *bch2_btree_node_mem_alloc(struct btree_trans *trans, bool pcpu_read_locks)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
-	struct btree *b;
+	struct list_head *freed = pcpu_read_locks
+		? &bc->freed_pcpu
+		: &bc->freed_nonpcpu;
+	struct btree *b, *b2;
 	u64 start_time = local_clock();
 	unsigned flags;
 
 	flags = memalloc_nofs_save();
 	mutex_lock(&bc->lock);
 
-	/*
-	 * btree_free() doesn't free memory; it sticks the node on the end of
-	 * the list. Check if there's any freed nodes there:
-	 */
-	list_for_each_entry(b, &bc->freeable, list)
-		if (!btree_node_reclaim(c, b))
-			goto got_node;
-
 	/*
 	 * We never free struct btree itself, just the memory that holds the on
 	 * disk node. Check the freed list before allocating a new one:
 	 */
-	list_for_each_entry(b, &bc->freed, list)
-		if (!btree_node_reclaim(c, b))
+	list_for_each_entry(b, freed, list)
+		if (!btree_node_reclaim(c, b)) {
+			list_del_init(&b->list);
 			goto got_node;
+		}
 
-	b = NULL;
-got_node:
-	if (b)
-		list_del_init(&b->list);
-	mutex_unlock(&bc->lock);
-
+	b = __btree_node_mem_alloc(c, GFP_NOWAIT|__GFP_NOWARN);
 	if (!b) {
-		b = kzalloc(sizeof(struct btree), GFP_KERNEL);
+		mutex_unlock(&bc->lock);
+		bch2_trans_unlock(trans);
+		b = __btree_node_mem_alloc(c, GFP_KERNEL);
 		if (!b)
 			goto err;
+		mutex_lock(&bc->lock);
+	}
 
-		bkey_btree_ptr_init(&b->key);
-		six_lock_init(&b->c.lock);
-		INIT_LIST_HEAD(&b->list);
-		INIT_LIST_HEAD(&b->write_blocked);
+	bch2_btree_lock_init(&b->c, pcpu_read_locks ? SIX_LOCK_INIT_PCPU : 0);
 
-		BUG_ON(!six_trylock_intent(&b->c.lock));
-		BUG_ON(!six_trylock_write(&b->c.lock));
-	}
+	BUG_ON(!six_trylock_intent(&b->c.lock));
+	BUG_ON(!six_trylock_write(&b->c.lock));
+got_node:
 
-	if (!b->data) {
-		if (__btree_node_data_alloc(c, b, __GFP_NOWARN|GFP_KERNEL))
-			goto err;
+	/*
+	 * btree_free() doesn't free memory; it sticks the node on the end of
+	 * the list. Check if there's any freed nodes there:
+	 */
+	list_for_each_entry(b2, &bc->freeable, list)
+		if (!btree_node_reclaim(c, b2)) {
+			swap(b->data, b2->data);
+			swap(b->aux_data, b2->aux_data);
+			btree_node_to_freedlist(bc, b2);
+			six_unlock_write(&b2->c.lock);
+			six_unlock_intent(&b2->c.lock);
+			goto got_mem;
+		}
 
-		mutex_lock(&bc->lock);
-		bc->used++;
-		mutex_unlock(&bc->lock);
+	mutex_unlock(&bc->lock);
+
+	if (btree_node_data_alloc(c, b, GFP_NOWAIT|__GFP_NOWARN)) {
+		bch2_trans_unlock(trans);
+		if (btree_node_data_alloc(c, b, GFP_KERNEL|__GFP_NOWARN))
+			goto err;
 	}
 
+	mutex_lock(&bc->lock);
+	bc->used++;
+got_mem:
+	mutex_unlock(&bc->lock);
+
 	BUG_ON(btree_node_hashed(b));
+	BUG_ON(btree_node_dirty(b));
 	BUG_ON(btree_node_write_in_flight(b));
 out:
 	b->flags		= 0;
@@ -581,7 +645,8 @@ out:
 	b->sib_u64s[0]		= 0;
 	b->sib_u64s[1]		= 0;
 	b->whiteout_u64s	= 0;
-	bch2_btree_keys_init(b, &c->expensive_debug_checks);
+	bch2_btree_keys_init(b);
+	set_btree_node_accessed(b);
 
 	bch2_time_stats_update(&c->times[BCH_TIME_btree_node_mem_alloc],
 			       start_time);
@@ -591,50 +656,66 @@ out:
 err:
 	mutex_lock(&bc->lock);
 
-	if (b) {
-		list_add(&b->list, &bc->freed);
-		six_unlock_write(&b->c.lock);
-		six_unlock_intent(&b->c.lock);
-	}
-
 	/* Try to cannibalize another cached btree node: */
 	if (bc->alloc_lock == current) {
-		b = btree_node_cannibalize(c);
-		list_del_init(&b->list);
-		mutex_unlock(&bc->lock);
+		b2 = btree_node_cannibalize(c);
+		clear_btree_node_just_written(b2);
+		bch2_btree_node_hash_remove(bc, b2);
+
+		if (b) {
+			swap(b->data, b2->data);
+			swap(b->aux_data, b2->aux_data);
+			btree_node_to_freedlist(bc, b2);
+			six_unlock_write(&b2->c.lock);
+			six_unlock_intent(&b2->c.lock);
+		} else {
+			b = b2;
+			list_del_init(&b->list);
+		}
 
-		bch2_btree_node_hash_remove(bc, b);
+		mutex_unlock(&bc->lock);
 
-		trace_btree_node_cannibalize(c);
+		trace_and_count(c, btree_cache_cannibalize, trans);
 		goto out;
 	}
 
 	mutex_unlock(&bc->lock);
 	memalloc_nofs_restore(flags);
-	return ERR_PTR(-ENOMEM);
+	return ERR_PTR(-BCH_ERR_ENOMEM_btree_node_mem_alloc);
 }
 
 /* Slowpath, don't want it inlined into btree_iter_traverse() */
-static noinline struct btree *bch2_btree_node_fill(struct bch_fs *c,
-				struct btree_iter *iter,
+static noinline struct btree *bch2_btree_node_fill(struct btree_trans *trans,
+				struct btree_path *path,
 				const struct bkey_i *k,
 				enum btree_id btree_id,
 				unsigned level,
 				enum six_lock_type lock_type,
 				bool sync)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
 	struct btree *b;
+	u32 seq;
 
 	BUG_ON(level + 1 >= BTREE_MAX_DEPTH);
 	/*
 	 * Parent node must be locked, else we could read in a btree node that's
 	 * been freed:
 	 */
-	if (iter && !bch2_btree_node_relock(iter, level + 1))
-		return ERR_PTR(-EINTR);
+	if (path && !bch2_btree_node_relock(trans, path, level + 1)) {
+		trace_and_count(c, trans_restart_relock_parent_for_fill, trans, _THIS_IP_, path);
+		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_fill_relock));
+	}
+
+	b = bch2_btree_node_mem_alloc(trans, level != 0);
+
+	if (bch2_err_matches(PTR_ERR_OR_ZERO(b), ENOMEM)) {
+		trans->memory_allocation_failure = true;
+		trace_and_count(c, trans_restart_memory_allocation_failure, trans, _THIS_IP_, path);
+		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_fill_mem_alloc_fail));
+	}
 
-	b = bch2_btree_node_mem_alloc(c);
 	if (IS_ERR(b))
 		return b;
 
@@ -654,59 +735,90 @@ static noinline struct btree *bch2_btree_node_fill(struct bch_fs *c,
 		return NULL;
 	}
 
-	/*
-	 * Unlock before doing IO:
-	 *
-	 * XXX: ideally should be dropping all btree node locks here
-	 */
-	if (iter && btree_node_read_locked(iter, level + 1))
-		btree_node_unlock(iter, level + 1);
-
-	bch2_btree_node_read(c, b, sync);
+	set_btree_node_read_in_flight(b);
 
 	six_unlock_write(&b->c.lock);
+	seq = six_lock_seq(&b->c.lock);
+	six_unlock_intent(&b->c.lock);
 
-	if (!sync) {
-		six_unlock_intent(&b->c.lock);
+	/* Unlock before doing IO: */
+	if (path && sync)
+		bch2_trans_unlock_noassert(trans);
+
+	bch2_btree_node_read(trans, b, sync);
+
+	if (!sync)
 		return NULL;
+
+	if (path) {
+		int ret = bch2_trans_relock(trans) ?:
+			bch2_btree_path_relock_intent(trans, path);
+		if (ret) {
+			BUG_ON(!trans->restarted);
+			return ERR_PTR(ret);
+		}
 	}
 
-	if (lock_type == SIX_LOCK_read)
-		six_lock_downgrade(&b->c.lock);
+	if (!six_relock_type(&b->c.lock, lock_type, seq)) {
+		if (path)
+			trace_and_count(c, trans_restart_relock_after_fill, trans, _THIS_IP_, path);
+		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_relock_after_fill));
+	}
 
 	return b;
 }
 
-static int lock_node_check_fn(struct six_lock *lock, void *p)
+static noinline void btree_bad_header(struct bch_fs *c, struct btree *b)
 {
-	struct btree *b = container_of(lock, struct btree, c.lock);
-	const struct bkey_i *k = p;
+	struct printbuf buf = PRINTBUF;
+
+	if (c->curr_recovery_pass <= BCH_RECOVERY_PASS_check_allocations)
+		return;
+
+	prt_printf(&buf,
+	       "btree node header doesn't match ptr\n"
+	       "btree %s level %u\n"
+	       "ptr: ",
+	       bch2_btree_id_str(b->c.btree_id), b->c.level);
+	bch2_bkey_val_to_text(&buf, c, bkey_i_to_s_c(&b->key));
+
+	prt_printf(&buf, "\nheader: btree %s level %llu\n"
+	       "min ",
+	       bch2_btree_id_str(BTREE_NODE_ID(b->data)),
+	       BTREE_NODE_LEVEL(b->data));
+	bch2_bpos_to_text(&buf, b->data->min_key);
 
-	return b->hash_val == btree_ptr_hash_val(k) ? 0 : -1;
+	prt_printf(&buf, "\nmax ");
+	bch2_bpos_to_text(&buf, b->data->max_key);
+
+	bch2_fs_inconsistent(c, "%s", buf.buf);
+	printbuf_exit(&buf);
 }
 
-/**
- * bch_btree_node_get - find a btree node in the cache and lock it, reading it
- * in from disk if necessary.
- *
- * If IO is necessary and running under generic_make_request, returns -EAGAIN.
- *
- * The btree node will have either a read or a write lock held, depending on
- * the @write parameter.
- */
-struct btree *bch2_btree_node_get(struct bch_fs *c, struct btree_iter *iter,
-				  const struct bkey_i *k, unsigned level,
-				  enum six_lock_type lock_type)
+static inline void btree_check_header(struct bch_fs *c, struct btree *b)
 {
+	if (b->c.btree_id != BTREE_NODE_ID(b->data) ||
+	    b->c.level != BTREE_NODE_LEVEL(b->data) ||
+	    !bpos_eq(b->data->max_key, b->key.k.p) ||
+	    (b->key.k.type == KEY_TYPE_btree_ptr_v2 &&
+	     !bpos_eq(b->data->min_key,
+		      bkey_i_to_btree_ptr_v2(&b->key)->v.min_key)))
+		btree_bad_header(c, b);
+}
+
+static struct btree *__bch2_btree_node_get(struct btree_trans *trans, struct btree_path *path,
+					   const struct bkey_i *k, unsigned level,
+					   enum six_lock_type lock_type,
+					   unsigned long trace_ip)
+{
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
 	struct btree *b;
 	struct bset_tree *t;
+	bool need_relock = false;
+	int ret;
 
 	EBUG_ON(level >= BTREE_MAX_DEPTH);
-
-	b = btree_node_mem_ptr(k);
-	if (b)
-		goto lock_node;
 retry:
 	b = btree_cache_find(bc, k);
 	if (unlikely(!b)) {
@@ -715,8 +827,9 @@ retry:
 		 * else we could read in a btree node from disk that's been
 		 * freed:
 		 */
-		b = bch2_btree_node_fill(c, iter, k, iter->btree_id,
+		b = bch2_btree_node_fill(trans, path, k, path->btree_id,
 					 level, lock_type, true);
+		need_relock = true;
 
 		/* We raced and found the btree node in the cache */
 		if (!b)
@@ -725,60 +838,143 @@ retry:
 		if (IS_ERR(b))
 			return b;
 	} else {
-lock_node:
-		/*
-		 * There's a potential deadlock with splits and insertions into
-		 * interior nodes we have to avoid:
-		 *
-		 * The other thread might be holding an intent lock on the node
-		 * we want, and they want to update its parent node so they're
-		 * going to upgrade their intent lock on the parent node to a
-		 * write lock.
-		 *
-		 * But if we're holding a read lock on the parent, and we're
-		 * trying to get the intent lock they're holding, we deadlock.
-		 *
-		 * So to avoid this we drop the read locks on parent nodes when
-		 * we're starting to take intent locks - and handle the race.
-		 *
-		 * The race is that they might be about to free the node we
-		 * want, and dropping our read lock on the parent node lets them
-		 * update the parent marking the node we want as freed, and then
-		 * free it:
-		 *
-		 * To guard against this, btree nodes are evicted from the cache
-		 * when they're freed - and b->hash_val is zeroed out, which we
-		 * check for after we lock the node.
-		 *
-		 * Then, bch2_btree_node_relock() on the parent will fail - because
-		 * the parent was modified, when the pointer to the node we want
-		 * was removed - and we'll bail out:
-		 */
-		if (btree_node_read_locked(iter, level + 1))
-			btree_node_unlock(iter, level + 1);
+		if (btree_node_read_locked(path, level + 1))
+			btree_node_unlock(trans, path, level + 1);
 
-		if (!btree_node_lock(b, k->k.p, level, iter, lock_type,
-				     lock_node_check_fn, (void *) k)) {
-			if (b->hash_val != btree_ptr_hash_val(k))
-				goto retry;
-			return ERR_PTR(-EINTR);
-		}
+		ret = btree_node_lock(trans, path, &b->c, level, lock_type, trace_ip);
+		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
+			return ERR_PTR(ret);
+
+		BUG_ON(ret);
 
 		if (unlikely(b->hash_val != btree_ptr_hash_val(k) ||
 			     b->c.level != level ||
 			     race_fault())) {
 			six_unlock_type(&b->c.lock, lock_type);
-			if (bch2_btree_node_relock(iter, level + 1))
+			if (bch2_btree_node_relock(trans, path, level + 1))
 				goto retry;
 
-			trace_trans_restart_btree_node_reused(iter->trans->ip);
-			return ERR_PTR(-EINTR);
+			trace_and_count(c, trans_restart_btree_node_reused, trans, trace_ip, path);
+			return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_lock_node_reused));
 		}
+
+		/* avoid atomic set bit if it's not needed: */
+		if (!btree_node_accessed(b))
+			set_btree_node_accessed(b);
 	}
 
-	/* XXX: waiting on IO with btree locks held: */
-	wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
-		       TASK_UNINTERRUPTIBLE);
+	if (unlikely(btree_node_read_in_flight(b))) {
+		u32 seq = six_lock_seq(&b->c.lock);
+
+		six_unlock_type(&b->c.lock, lock_type);
+		bch2_trans_unlock(trans);
+		need_relock = true;
+
+		bch2_btree_node_wait_on_read(b);
+
+		/*
+		 * should_be_locked is not set on this path yet, so we need to
+		 * relock it specifically:
+		 */
+		if (!six_relock_type(&b->c.lock, lock_type, seq))
+			goto retry;
+	}
+
+	if (unlikely(need_relock)) {
+		ret = bch2_trans_relock(trans) ?:
+			bch2_btree_path_relock_intent(trans, path);
+		if (ret) {
+			six_unlock_type(&b->c.lock, lock_type);
+			return ERR_PTR(ret);
+		}
+	}
+
+	prefetch(b->aux_data);
+
+	for_each_bset(b, t) {
+		void *p = (u64 *) b->aux_data + t->aux_data_offset;
+
+		prefetch(p + L1_CACHE_BYTES * 0);
+		prefetch(p + L1_CACHE_BYTES * 1);
+		prefetch(p + L1_CACHE_BYTES * 2);
+	}
+
+	if (unlikely(btree_node_read_error(b))) {
+		six_unlock_type(&b->c.lock, lock_type);
+		return ERR_PTR(-EIO);
+	}
+
+	EBUG_ON(b->c.btree_id != path->btree_id);
+	EBUG_ON(BTREE_NODE_LEVEL(b->data) != level);
+	btree_check_header(c, b);
+
+	return b;
+}
+
+/**
+ * bch2_btree_node_get - find a btree node in the cache and lock it, reading it
+ * in from disk if necessary.
+ *
+ * @trans:	btree transaction object
+ * @path:	btree_path being traversed
+ * @k:		pointer to btree node (generally KEY_TYPE_btree_ptr_v2)
+ * @level:	level of btree node being looked up (0 == leaf node)
+ * @lock_type:	SIX_LOCK_read or SIX_LOCK_intent
+ * @trace_ip:	ip of caller of btree iterator code (i.e. caller of bch2_btree_iter_peek())
+ *
+ * The btree node will have either a read or a write lock held, depending on
+ * the @write parameter.
+ *
+ * Returns: btree node or ERR_PTR()
+ */
+struct btree *bch2_btree_node_get(struct btree_trans *trans, struct btree_path *path,
+				  const struct bkey_i *k, unsigned level,
+				  enum six_lock_type lock_type,
+				  unsigned long trace_ip)
+{
+	struct bch_fs *c = trans->c;
+	struct btree *b;
+	struct bset_tree *t;
+	int ret;
+
+	EBUG_ON(level >= BTREE_MAX_DEPTH);
+
+	b = btree_node_mem_ptr(k);
+
+	/*
+	 * Check b->hash_val _before_ calling btree_node_lock() - this might not
+	 * be the node we want anymore, and trying to lock the wrong node could
+	 * cause an unneccessary transaction restart:
+	 */
+	if (unlikely(!c->opts.btree_node_mem_ptr_optimization ||
+		     !b ||
+		     b->hash_val != btree_ptr_hash_val(k)))
+		return __bch2_btree_node_get(trans, path, k, level, lock_type, trace_ip);
+
+	if (btree_node_read_locked(path, level + 1))
+		btree_node_unlock(trans, path, level + 1);
+
+	ret = btree_node_lock(trans, path, &b->c, level, lock_type, trace_ip);
+	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
+		return ERR_PTR(ret);
+
+	BUG_ON(ret);
+
+	if (unlikely(b->hash_val != btree_ptr_hash_val(k) ||
+		     b->c.level != level ||
+		     race_fault())) {
+		six_unlock_type(&b->c.lock, lock_type);
+		if (bch2_btree_node_relock(trans, path, level + 1))
+			return __bch2_btree_node_get(trans, path, k, level, lock_type, trace_ip);
+
+		trace_and_count(c, trans_restart_btree_node_reused, trans, trace_ip, path);
+		return ERR_PTR(btree_trans_restart(trans, BCH_ERR_transaction_restart_lock_node_reused));
+	}
+
+	if (unlikely(btree_node_read_in_flight(b))) {
+		six_unlock_type(&b->c.lock, lock_type);
+		return __bch2_btree_node_get(trans, path, k, level, lock_type, trace_ip);
+	}
 
 	prefetch(b->aux_data);
 
@@ -799,18 +995,20 @@ lock_node:
 		return ERR_PTR(-EIO);
 	}
 
-	EBUG_ON(b->c.btree_id != iter->btree_id ||
-		BTREE_NODE_LEVEL(b->data) != level ||
-		bkey_cmp(b->data->max_key, k->k.p));
+	EBUG_ON(b->c.btree_id != path->btree_id);
+	EBUG_ON(BTREE_NODE_LEVEL(b->data) != level);
+	btree_check_header(c, b);
 
 	return b;
 }
 
-struct btree *bch2_btree_node_get_noiter(struct bch_fs *c,
+struct btree *bch2_btree_node_get_noiter(struct btree_trans *trans,
 					 const struct bkey_i *k,
 					 enum btree_id btree_id,
-					 unsigned level)
+					 unsigned level,
+					 bool nofill)
 {
+	struct bch_fs *c = trans->c;
 	struct btree_cache *bc = &c->btree_cache;
 	struct btree *b;
 	struct bset_tree *t;
@@ -818,26 +1016,37 @@ struct btree *bch2_btree_node_get_noiter(struct bch_fs *c,
 
 	EBUG_ON(level >= BTREE_MAX_DEPTH);
 
-	b = btree_node_mem_ptr(k);
-	if (b)
-		goto lock_node;
+	if (c->opts.btree_node_mem_ptr_optimization) {
+		b = btree_node_mem_ptr(k);
+		if (b)
+			goto lock_node;
+	}
 retry:
 	b = btree_cache_find(bc, k);
 	if (unlikely(!b)) {
-		b = bch2_btree_node_fill(c, NULL, k, btree_id,
+		if (nofill)
+			goto out;
+
+		b = bch2_btree_node_fill(trans, NULL, k, btree_id,
 					 level, SIX_LOCK_read, true);
 
 		/* We raced and found the btree node in the cache */
 		if (!b)
 			goto retry;
 
+		if (IS_ERR(b) &&
+		    !bch2_btree_cache_cannibalize_lock(trans, NULL))
+			goto retry;
+
 		if (IS_ERR(b))
-			return b;
+			goto out;
 	} else {
 lock_node:
-		ret = six_lock_read(&b->c.lock, lock_node_check_fn, (void *) k);
-		if (ret)
-			goto retry;
+		ret = btree_node_lock_nopath(trans, &b->c, SIX_LOCK_read, _THIS_IP_);
+		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
+			return ERR_PTR(ret);
+
+		BUG_ON(ret);
 
 		if (unlikely(b->hash_val != btree_ptr_hash_val(k) ||
 			     b->c.btree_id != btree_id ||
@@ -848,8 +1057,7 @@ lock_node:
 	}
 
 	/* XXX: waiting on IO with btree locks held: */
-	wait_on_bit_io(&b->flags, BTREE_NODE_read_in_flight,
-		       TASK_UNINTERRUPTIBLE);
+	__bch2_btree_node_wait_on_read(b);
 
 	prefetch(b->aux_data);
 
@@ -867,188 +1075,137 @@ lock_node:
 
 	if (unlikely(btree_node_read_error(b))) {
 		six_unlock_read(&b->c.lock);
-		return ERR_PTR(-EIO);
+		b = ERR_PTR(-EIO);
+		goto out;
 	}
 
-	EBUG_ON(b->c.btree_id != btree_id ||
-		BTREE_NODE_LEVEL(b->data) != level ||
-		bkey_cmp(b->data->max_key, k->k.p));
-
+	EBUG_ON(b->c.btree_id != btree_id);
+	EBUG_ON(BTREE_NODE_LEVEL(b->data) != level);
+	btree_check_header(c, b);
+out:
+	bch2_btree_cache_cannibalize_unlock(trans);
 	return b;
 }
 
-struct btree *bch2_btree_node_get_sibling(struct bch_fs *c,
-					  struct btree_iter *iter,
-					  struct btree *b,
-					  enum btree_node_sibling sib)
+int bch2_btree_node_prefetch(struct btree_trans *trans,
+			     struct btree_path *path,
+			     const struct bkey_i *k,
+			     enum btree_id btree_id, unsigned level)
 {
-	struct btree_trans *trans = iter->trans;
-	struct btree *parent;
-	struct btree_node_iter node_iter;
-	struct bkey_packed *k;
-	BKEY_PADDED(k) tmp;
-	struct btree *ret = NULL;
-	unsigned level = b->c.level;
-
-	parent = btree_iter_node(iter, level + 1);
-	if (!parent)
-		return NULL;
-
-	/*
-	 * There's a corner case where a btree_iter might have a node locked
-	 * that is just outside its current pos - when
-	 * bch2_btree_iter_set_pos_same_leaf() gets to the end of the node.
-	 *
-	 * But the lock ordering checks in __bch2_btree_node_lock() go off of
-	 * iter->pos, not the node's key: so if the iterator is marked as
-	 * needing to be traversed, we risk deadlock if we don't bail out here:
-	 */
-	if (iter->uptodate >= BTREE_ITER_NEED_TRAVERSE)
-		return ERR_PTR(-EINTR);
-
-	if (!bch2_btree_node_relock(iter, level + 1)) {
-		ret = ERR_PTR(-EINTR);
-		goto out;
-	}
-
-	node_iter = iter->l[parent->c.level].iter;
-
-	k = bch2_btree_node_iter_peek_all(&node_iter, parent);
-	BUG_ON(bkey_cmp_left_packed(parent, k, &b->key.k.p));
-
-	k = sib == btree_prev_sib
-		? bch2_btree_node_iter_prev(&node_iter, parent)
-		: (bch2_btree_node_iter_advance(&node_iter, parent),
-		   bch2_btree_node_iter_peek(&node_iter, parent));
-	if (!k)
-		goto out;
-
-	bch2_bkey_unpack(parent, &tmp.k, k);
-
-	ret = bch2_btree_node_get(c, iter, &tmp.k, level,
-				  SIX_LOCK_intent);
-
-	if (PTR_ERR_OR_ZERO(ret) == -EINTR && !trans->nounlock) {
-		struct btree_iter *linked;
+	struct bch_fs *c = trans->c;
+	struct btree_cache *bc = &c->btree_cache;
+	struct btree *b;
 
-		if (!bch2_btree_node_relock(iter, level + 1))
-			goto out;
+	BUG_ON(trans && !btree_node_locked(path, level + 1));
+	BUG_ON(level >= BTREE_MAX_DEPTH);
 
-		/*
-		 * We might have got -EINTR because trylock failed, and we're
-		 * holding other locks that would cause us to deadlock:
-		 */
-		trans_for_each_iter(trans, linked)
-			if (btree_iter_cmp(iter, linked) < 0)
-				__bch2_btree_iter_unlock(linked);
+	b = btree_cache_find(bc, k);
+	if (b)
+		return 0;
 
-		if (sib == btree_prev_sib)
-			btree_node_unlock(iter, level);
+	b = bch2_btree_node_fill(trans, path, k, btree_id,
+				 level, SIX_LOCK_read, false);
+	return PTR_ERR_OR_ZERO(b);
+}
 
-		ret = bch2_btree_node_get(c, iter, &tmp.k, level,
-					  SIX_LOCK_intent);
+void bch2_btree_node_evict(struct btree_trans *trans, const struct bkey_i *k)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_cache *bc = &c->btree_cache;
+	struct btree *b;
 
-		/*
-		 * before btree_iter_relock() calls btree_iter_verify_locks():
-		 */
-		if (btree_lock_want(iter, level + 1) == BTREE_NODE_UNLOCKED)
-			btree_node_unlock(iter, level + 1);
+	b = btree_cache_find(bc, k);
+	if (!b)
+		return;
+wait_on_io:
+	/* not allowed to wait on io with btree locks held: */
 
-		if (!bch2_btree_node_relock(iter, level)) {
-			btree_iter_set_dirty(iter, BTREE_ITER_NEED_RELOCK);
+	/* XXX we're called from btree_gc which will be holding other btree
+	 * nodes locked
+	 */
+	__bch2_btree_node_wait_on_read(b);
+	__bch2_btree_node_wait_on_write(b);
 
-			if (!IS_ERR(ret)) {
-				six_unlock_intent(&ret->c.lock);
-				ret = ERR_PTR(-EINTR);
-			}
-		}
+	btree_node_lock_nopath_nofail(trans, &b->c, SIX_LOCK_intent);
+	btree_node_lock_nopath_nofail(trans, &b->c, SIX_LOCK_write);
 
-		bch2_trans_relock(trans);
+	if (btree_node_dirty(b)) {
+		__bch2_btree_node_write(c, b, BTREE_WRITE_cache_reclaim);
+		six_unlock_write(&b->c.lock);
+		six_unlock_intent(&b->c.lock);
+		goto wait_on_io;
 	}
-out:
-	if (btree_lock_want(iter, level + 1) == BTREE_NODE_UNLOCKED)
-		btree_node_unlock(iter, level + 1);
-
-	if (PTR_ERR_OR_ZERO(ret) == -EINTR)
-		bch2_btree_iter_upgrade(iter, level + 2);
-
-	BUG_ON(!IS_ERR(ret) && !btree_node_locked(iter, level));
 
-	if (!IS_ERR_OR_NULL(ret)) {
-		struct btree *n1 = ret, *n2 = b;
+	BUG_ON(btree_node_dirty(b));
 
-		if (sib != btree_prev_sib)
-			swap(n1, n2);
-
-		BUG_ON(bkey_cmp(bkey_successor(n1->key.k.p),
-				n2->data->min_key));
-	}
-
-	bch2_btree_trans_verify_locks(trans);
+	mutex_lock(&bc->lock);
+	btree_node_data_free(c, b);
+	bch2_btree_node_hash_remove(bc, b);
+	mutex_unlock(&bc->lock);
 
-	return ret;
+	six_unlock_write(&b->c.lock);
+	six_unlock_intent(&b->c.lock);
 }
 
-void bch2_btree_node_prefetch(struct bch_fs *c, struct btree_iter *iter,
-			      const struct bkey_i *k, unsigned level)
+const char *bch2_btree_id_str(enum btree_id btree)
 {
-	struct btree_cache *bc = &c->btree_cache;
-	struct btree *b;
-
-	BUG_ON(!btree_node_locked(iter, level + 1));
-	BUG_ON(level >= BTREE_MAX_DEPTH);
-
-	b = btree_cache_find(bc, k);
-	if (b)
-		return;
+	return btree < BTREE_ID_NR ? __bch2_btree_ids[btree] : "(unknown)";
+}
 
-	bch2_btree_node_fill(c, iter, k, iter->btree_id,
-			     level, SIX_LOCK_read, false);
+void bch2_btree_pos_to_text(struct printbuf *out, struct bch_fs *c, const struct btree *b)
+{
+	prt_printf(out, "%s level %u/%u\n  ",
+	       bch2_btree_id_str(b->c.btree_id),
+	       b->c.level,
+	       bch2_btree_id_root(c, b->c.btree_id)->level);
+	bch2_bkey_val_to_text(out, c, bkey_i_to_s_c(&b->key));
 }
 
-void bch2_btree_node_to_text(struct printbuf *out, struct bch_fs *c,
-			     struct btree *b)
+void bch2_btree_node_to_text(struct printbuf *out, struct bch_fs *c, const struct btree *b)
 {
-	const struct bkey_format *f = &b->format;
 	struct bset_stats stats;
 
 	memset(&stats, 0, sizeof(stats));
 
 	bch2_btree_keys_stats(b, &stats);
 
-	pr_buf(out,
-	       "l %u %llu:%llu - %llu:%llu:\n"
-	       "    ptrs: ",
-	       b->c.level,
-	       b->data->min_key.inode,
-	       b->data->min_key.offset,
-	       b->data->max_key.inode,
-	       b->data->max_key.offset);
+	prt_printf(out, "l %u ", b->c.level);
+	bch2_bpos_to_text(out, b->data->min_key);
+	prt_printf(out, " - ");
+	bch2_bpos_to_text(out, b->data->max_key);
+	prt_printf(out, ":\n"
+	       "    ptrs: ");
 	bch2_val_to_text(out, c, bkey_i_to_s_c(&b->key));
-	pr_buf(out, "\n"
-	       "    format: u64s %u fields %u %u %u %u %u\n"
+	prt_newline(out);
+
+	prt_printf(out,
+	       "    format: ");
+	bch2_bkey_format_to_text(out, &b->format);
+
+	prt_printf(out,
 	       "    unpack fn len: %u\n"
 	       "    bytes used %zu/%zu (%zu%% full)\n"
-	       "    sib u64s: %u, %u (merge threshold %zu)\n"
+	       "    sib u64s: %u, %u (merge threshold %u)\n"
 	       "    nr packed keys %u\n"
 	       "    nr unpacked keys %u\n"
 	       "    floats %zu\n"
 	       "    failed unpacked %zu\n",
-	       f->key_u64s,
-	       f->bits_per_field[0],
-	       f->bits_per_field[1],
-	       f->bits_per_field[2],
-	       f->bits_per_field[3],
-	       f->bits_per_field[4],
 	       b->unpack_fn_len,
 	       b->nr.live_u64s * sizeof(u64),
 	       btree_bytes(c) - sizeof(struct btree_node),
 	       b->nr.live_u64s * 100 / btree_max_u64s(c),
 	       b->sib_u64s[0],
 	       b->sib_u64s[1],
-	       BTREE_FOREGROUND_MERGE_THRESHOLD(c),
+	       c->btree_foreground_merge_threshold,
 	       b->nr.packed_keys,
 	       b->nr.unpacked_keys,
 	       stats.floats,
 	       stats.failed);
 }
+
+void bch2_btree_cache_to_text(struct printbuf *out, const struct bch_fs *c)
+{
+	prt_printf(out, "nr nodes:\t\t%u\n", c->btree_cache.used);
+	prt_printf(out, "nr dirty:\t\t%u\n", atomic_read(&c->btree_cache.dirty));
+	prt_printf(out, "cannibalize lock:\t%p\n", c->btree_cache.alloc_lock);
+}