1 files changed, 647 insertions, 0 deletions

diff --git a/c_src/libbcachefs/btree_write_buffer.c b/c_src/libbcachefs/btree_write_buffer.c
new file mode 100644
index 00000000..5c1169c7
--- /dev/null
+++ b/c_src/libbcachefs/btree_write_buffer.c
@@ -0,0 +1,647 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "btree_locking.h"
+#include "btree_update.h"
+#include "btree_update_interior.h"
+#include "btree_write_buffer.h"
+#include "error.h"
+#include "journal.h"
+#include "journal_io.h"
+#include "journal_reclaim.h"
+
+#include <linux/prefetch.h>
+
+static int bch2_btree_write_buffer_journal_flush(struct journal *,
+				struct journal_entry_pin *, u64);
+
+static int bch2_journal_keys_to_write_buffer(struct bch_fs *, struct journal_buf *);
+
+static inline bool __wb_key_ref_cmp(const struct wb_key_ref *l, const struct wb_key_ref *r)
+{
+	return (cmp_int(l->hi, r->hi) ?:
+		cmp_int(l->mi, r->mi) ?:
+		cmp_int(l->lo, r->lo)) >= 0;
+}
+
+static inline bool wb_key_ref_cmp(const struct wb_key_ref *l, const struct wb_key_ref *r)
+{
+#ifdef CONFIG_X86_64
+	int cmp;
+
+	asm("mov   (%[l]), %%rax;"
+	    "sub   (%[r]), %%rax;"
+	    "mov  8(%[l]), %%rax;"
+	    "sbb  8(%[r]), %%rax;"
+	    "mov 16(%[l]), %%rax;"
+	    "sbb 16(%[r]), %%rax;"
+	    : "=@ccae" (cmp)
+	    : [l] "r" (l), [r] "r" (r)
+	    : "rax", "cc");
+
+	EBUG_ON(cmp != __wb_key_ref_cmp(l, r));
+	return cmp;
+#else
+	return __wb_key_ref_cmp(l, r);
+#endif
+}
+
+/* Compare excluding idx, the low 24 bits: */
+static inline bool wb_key_eq(const void *_l, const void *_r)
+{
+	const struct wb_key_ref *l = _l;
+	const struct wb_key_ref *r = _r;
+
+	return !((l->hi ^ r->hi)|
+		 (l->mi ^ r->mi)|
+		 ((l->lo >> 24) ^ (r->lo >> 24)));
+}
+
+static noinline void wb_sort(struct wb_key_ref *base, size_t num)
+{
+	size_t n = num, a = num / 2;
+
+	if (!a)		/* num < 2 || size == 0 */
+		return;
+
+	for (;;) {
+		size_t b, c, d;
+
+		if (a)			/* Building heap: sift down --a */
+			--a;
+		else if (--n)		/* Sorting: Extract root to --n */
+			swap(base[0], base[n]);
+		else			/* Sort complete */
+			break;
+
+		/*
+		 * Sift element at "a" down into heap.  This is the
+		 * "bottom-up" variant, which significantly reduces
+		 * calls to cmp_func(): we find the sift-down path all
+		 * the way to the leaves (one compare per level), then
+		 * backtrack to find where to insert the target element.
+		 *
+		 * Because elements tend to sift down close to the leaves,
+		 * this uses fewer compares than doing two per level
+		 * on the way down.  (A bit more than half as many on
+		 * average, 3/4 worst-case.)
+		 */
+		for (b = a; c = 2*b + 1, (d = c + 1) < n;)
+			b = wb_key_ref_cmp(base + c, base + d) ? c : d;
+		if (d == n)		/* Special case last leaf with no sibling */
+			b = c;
+
+		/* Now backtrack from "b" to the correct location for "a" */
+		while (b != a && wb_key_ref_cmp(base + a, base + b))
+			b = (b - 1) / 2;
+		c = b;			/* Where "a" belongs */
+		while (b != a) {	/* Shift it into place */
+			b = (b - 1) / 2;
+			swap(base[b], base[c]);
+		}
+	}
+}
+
+static noinline int wb_flush_one_slowpath(struct btree_trans *trans,
+					  struct btree_iter *iter,
+					  struct btree_write_buffered_key *wb)
+{
+	struct btree_path *path = btree_iter_path(trans, iter);
+
+	bch2_btree_node_unlock_write(trans, path, path->l[0].b);
+
+	trans->journal_res.seq = wb->journal_seq;
+
+	return bch2_trans_update(trans, iter, &wb->k,
+				 BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE) ?:
+		bch2_trans_commit(trans, NULL, NULL,
+				  BCH_TRANS_COMMIT_no_enospc|
+				  BCH_TRANS_COMMIT_no_check_rw|
+				  BCH_TRANS_COMMIT_no_journal_res|
+				  BCH_TRANS_COMMIT_journal_reclaim);
+}
+
+static inline int wb_flush_one(struct btree_trans *trans, struct btree_iter *iter,
+			       struct btree_write_buffered_key *wb,
+			       bool *write_locked, size_t *fast)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_path *path;
+	int ret;
+
+	EBUG_ON(!wb->journal_seq);
+	EBUG_ON(!c->btree_write_buffer.flushing.pin.seq);
+	EBUG_ON(c->btree_write_buffer.flushing.pin.seq > wb->journal_seq);
+
+	ret = bch2_btree_iter_traverse(iter);
+	if (ret)
+		return ret;
+
+	/*
+	 * We can't clone a path that has write locks: unshare it now, before
+	 * set_pos and traverse():
+	 */
+	if (btree_iter_path(trans, iter)->ref > 1)
+		iter->path = __bch2_btree_path_make_mut(trans, iter->path, true, _THIS_IP_);
+
+	path = btree_iter_path(trans, iter);
+
+	if (!*write_locked) {
+		ret = bch2_btree_node_lock_write(trans, path, &path->l[0].b->c);
+		if (ret)
+			return ret;
+
+		bch2_btree_node_prep_for_write(trans, path, path->l[0].b);
+		*write_locked = true;
+	}
+
+	if (unlikely(!bch2_btree_node_insert_fits(c, path->l[0].b, wb->k.k.u64s))) {
+		*write_locked = false;
+		return wb_flush_one_slowpath(trans, iter, wb);
+	}
+
+	bch2_btree_insert_key_leaf(trans, path, &wb->k, wb->journal_seq);
+	(*fast)++;
+	return 0;
+}
+
+/*
+ * Update a btree with a write buffered key using the journal seq of the
+ * original write buffer insert.
+ *
+ * It is not safe to rejournal the key once it has been inserted into the write
+ * buffer because that may break recovery ordering. For example, the key may
+ * have already been modified in the active write buffer in a seq that comes
+ * before the current transaction. If we were to journal this key again and
+ * crash, recovery would process updates in the wrong order.
+ */
+static int
+btree_write_buffered_insert(struct btree_trans *trans,
+			  struct btree_write_buffered_key *wb)
+{
+	struct btree_iter iter;
+	int ret;
+
+	bch2_trans_iter_init(trans, &iter, wb->btree, bkey_start_pos(&wb->k.k),
+			     BTREE_ITER_CACHED|BTREE_ITER_INTENT);
+
+	trans->journal_res.seq = wb->journal_seq;
+
+	ret   = bch2_btree_iter_traverse(&iter) ?:
+		bch2_trans_update(trans, &iter, &wb->k,
+				  BTREE_UPDATE_INTERNAL_SNAPSHOT_NODE);
+	bch2_trans_iter_exit(trans, &iter);
+	return ret;
+}
+
+static void move_keys_from_inc_to_flushing(struct btree_write_buffer *wb)
+{
+	struct bch_fs *c = container_of(wb, struct bch_fs, btree_write_buffer);
+	struct journal *j = &c->journal;
+
+	if (!wb->inc.keys.nr)
+		return;
+
+	bch2_journal_pin_add(j, wb->inc.keys.data[0].journal_seq, &wb->flushing.pin,
+			     bch2_btree_write_buffer_journal_flush);
+
+	darray_resize(&wb->flushing.keys, min_t(size_t, 1U << 20, wb->flushing.keys.nr + wb->inc.keys.nr));
+	darray_resize(&wb->sorted, wb->flushing.keys.size);
+
+	if (!wb->flushing.keys.nr && wb->sorted.size >= wb->inc.keys.nr) {
+		swap(wb->flushing.keys, wb->inc.keys);
+		goto out;
+	}
+
+	size_t nr = min(darray_room(wb->flushing.keys),
+			wb->sorted.size - wb->flushing.keys.nr);
+	nr = min(nr, wb->inc.keys.nr);
+
+	memcpy(&darray_top(wb->flushing.keys),
+	       wb->inc.keys.data,
+	       sizeof(wb->inc.keys.data[0]) * nr);
+
+	memmove(wb->inc.keys.data,
+		wb->inc.keys.data + nr,
+	       sizeof(wb->inc.keys.data[0]) * (wb->inc.keys.nr - nr));
+
+	wb->flushing.keys.nr	+= nr;
+	wb->inc.keys.nr		-= nr;
+out:
+	if (!wb->inc.keys.nr)
+		bch2_journal_pin_drop(j, &wb->inc.pin);
+	else
+		bch2_journal_pin_update(j, wb->inc.keys.data[0].journal_seq, &wb->inc.pin,
+					bch2_btree_write_buffer_journal_flush);
+
+	if (j->watermark) {
+		spin_lock(&j->lock);
+		bch2_journal_set_watermark(j);
+		spin_unlock(&j->lock);
+	}
+
+	BUG_ON(wb->sorted.size < wb->flushing.keys.nr);
+}
+
+static int bch2_btree_write_buffer_flush_locked(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+	struct journal *j = &c->journal;
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+	struct btree_iter iter = { NULL };
+	size_t skipped = 0, fast = 0, slowpath = 0;
+	bool write_locked = false;
+	int ret = 0;
+
+	bch2_trans_unlock(trans);
+	bch2_trans_begin(trans);
+
+	mutex_lock(&wb->inc.lock);
+	move_keys_from_inc_to_flushing(wb);
+	mutex_unlock(&wb->inc.lock);
+
+	for (size_t i = 0; i < wb->flushing.keys.nr; i++) {
+		wb->sorted.data[i].idx = i;
+		wb->sorted.data[i].btree = wb->flushing.keys.data[i].btree;
+		memcpy(&wb->sorted.data[i].pos, &wb->flushing.keys.data[i].k.k.p, sizeof(struct bpos));
+	}
+	wb->sorted.nr = wb->flushing.keys.nr;
+
+	/*
+	 * We first sort so that we can detect and skip redundant updates, and
+	 * then we attempt to flush in sorted btree order, as this is most
+	 * efficient.
+	 *
+	 * However, since we're not flushing in the order they appear in the
+	 * journal we won't be able to drop our journal pin until everything is
+	 * flushed - which means this could deadlock the journal if we weren't
+	 * passing BCH_TRANS_COMMIT_journal_reclaim. This causes the update to fail
+	 * if it would block taking a journal reservation.
+	 *
+	 * If that happens, simply skip the key so we can optimistically insert
+	 * as many keys as possible in the fast path.
+	 */
+	wb_sort(wb->sorted.data, wb->sorted.nr);
+
+	darray_for_each(wb->sorted, i) {
+		struct btree_write_buffered_key *k = &wb->flushing.keys.data[i->idx];
+
+		for (struct wb_key_ref *n = i + 1; n < min(i + 4, &darray_top(wb->sorted)); n++)
+			prefetch(&wb->flushing.keys.data[n->idx]);
+
+		BUG_ON(!k->journal_seq);
+
+		if (i + 1 < &darray_top(wb->sorted) &&
+		    wb_key_eq(i, i + 1)) {
+			struct btree_write_buffered_key *n = &wb->flushing.keys.data[i[1].idx];
+
+			skipped++;
+			n->journal_seq = min_t(u64, n->journal_seq, k->journal_seq);
+			k->journal_seq = 0;
+			continue;
+		}
+
+		if (write_locked) {
+			struct btree_path *path = btree_iter_path(trans, &iter);
+
+			if (path->btree_id != i->btree ||
+			    bpos_gt(k->k.k.p, path->l[0].b->key.k.p)) {
+				bch2_btree_node_unlock_write(trans, path, path->l[0].b);
+				write_locked = false;
+			}
+		}
+
+		if (!iter.path || iter.btree_id != k->btree) {
+			bch2_trans_iter_exit(trans, &iter);
+			bch2_trans_iter_init(trans, &iter, k->btree, k->k.k.p,
+					     BTREE_ITER_INTENT|BTREE_ITER_ALL_SNAPSHOTS);
+		}
+
+		bch2_btree_iter_set_pos(&iter, k->k.k.p);
+		btree_iter_path(trans, &iter)->preserve = false;
+
+		do {
+			if (race_fault()) {
+				ret = -BCH_ERR_journal_reclaim_would_deadlock;
+				break;
+			}
+
+			ret = wb_flush_one(trans, &iter, k, &write_locked, &fast);
+			if (!write_locked)
+				bch2_trans_begin(trans);
+		} while (bch2_err_matches(ret, BCH_ERR_transaction_restart));
+
+		if (!ret) {
+			k->journal_seq = 0;
+		} else if (ret == -BCH_ERR_journal_reclaim_would_deadlock) {
+			slowpath++;
+			ret = 0;
+		} else
+			break;
+	}
+
+	if (write_locked) {
+		struct btree_path *path = btree_iter_path(trans, &iter);
+		bch2_btree_node_unlock_write(trans, path, path->l[0].b);
+	}
+	bch2_trans_iter_exit(trans, &iter);
+
+	if (ret)
+		goto err;
+
+	if (slowpath) {
+		/*
+		 * Flush in the order they were present in the journal, so that
+		 * we can release journal pins:
+		 * The fastpath zapped the seq of keys that were successfully flushed so
+		 * we can skip those here.
+		 */
+		trace_and_count(c, write_buffer_flush_slowpath, trans, slowpath, wb->flushing.keys.nr);
+
+		darray_for_each(wb->flushing.keys, i) {
+			if (!i->journal_seq)
+				continue;
+
+			bch2_journal_pin_update(j, i->journal_seq, &wb->flushing.pin,
+						bch2_btree_write_buffer_journal_flush);
+
+			bch2_trans_begin(trans);
+
+			ret = commit_do(trans, NULL, NULL,
+					BCH_WATERMARK_reclaim|
+					BCH_TRANS_COMMIT_no_check_rw|
+					BCH_TRANS_COMMIT_no_enospc|
+					BCH_TRANS_COMMIT_no_journal_res|
+					BCH_TRANS_COMMIT_journal_reclaim,
+					btree_write_buffered_insert(trans, i));
+			if (ret)
+				goto err;
+		}
+	}
+err:
+	bch2_fs_fatal_err_on(ret, c, "%s: insert error %s", __func__, bch2_err_str(ret));
+	trace_write_buffer_flush(trans, wb->flushing.keys.nr, skipped, fast, 0);
+	bch2_journal_pin_drop(j, &wb->flushing.pin);
+	wb->flushing.keys.nr = 0;
+	return ret;
+}
+
+static int fetch_wb_keys_from_journal(struct bch_fs *c, u64 seq)
+{
+	struct journal *j = &c->journal;
+	struct journal_buf *buf;
+	int ret = 0;
+
+	while (!ret && (buf = bch2_next_write_buffer_flush_journal_buf(j, seq))) {
+		ret = bch2_journal_keys_to_write_buffer(c, buf);
+		mutex_unlock(&j->buf_lock);
+	}
+
+	return ret;
+}
+
+static int btree_write_buffer_flush_seq(struct btree_trans *trans, u64 seq)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+	int ret = 0, fetch_from_journal_err;
+
+	do {
+		bch2_trans_unlock(trans);
+
+		fetch_from_journal_err = fetch_wb_keys_from_journal(c, seq);
+
+		/*
+		 * On memory allocation failure, bch2_btree_write_buffer_flush_locked()
+		 * is not guaranteed to empty wb->inc:
+		 */
+		mutex_lock(&wb->flushing.lock);
+		ret = bch2_btree_write_buffer_flush_locked(trans);
+		mutex_unlock(&wb->flushing.lock);
+	} while (!ret &&
+		 (fetch_from_journal_err ||
+		  (wb->inc.pin.seq && wb->inc.pin.seq <= seq) ||
+		  (wb->flushing.pin.seq && wb->flushing.pin.seq <= seq)));
+
+	return ret;
+}
+
+static int bch2_btree_write_buffer_journal_flush(struct journal *j,
+				struct journal_entry_pin *_pin, u64 seq)
+{
+	struct bch_fs *c = container_of(j, struct bch_fs, journal);
+
+	return bch2_trans_run(c, btree_write_buffer_flush_seq(trans, seq));
+}
+
+int bch2_btree_write_buffer_flush_sync(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+
+	trace_and_count(c, write_buffer_flush_sync, trans, _RET_IP_);
+
+	return btree_write_buffer_flush_seq(trans, journal_cur_seq(&c->journal));
+}
+
+int bch2_btree_write_buffer_flush_nocheck_rw(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+	int ret = 0;
+
+	if (mutex_trylock(&wb->flushing.lock)) {
+		ret = bch2_btree_write_buffer_flush_locked(trans);
+		mutex_unlock(&wb->flushing.lock);
+	}
+
+	return ret;
+}
+
+int bch2_btree_write_buffer_tryflush(struct btree_trans *trans)
+{
+	struct bch_fs *c = trans->c;
+
+	if (!bch2_write_ref_tryget(c, BCH_WRITE_REF_btree_write_buffer))
+		return -BCH_ERR_erofs_no_writes;
+
+	int ret = bch2_btree_write_buffer_flush_nocheck_rw(trans);
+	bch2_write_ref_put(c, BCH_WRITE_REF_btree_write_buffer);
+	return ret;
+}
+
+static void bch2_btree_write_buffer_flush_work(struct work_struct *work)
+{
+	struct bch_fs *c = container_of(work, struct bch_fs, btree_write_buffer.flush_work);
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+	int ret;
+
+	mutex_lock(&wb->flushing.lock);
+	do {
+		ret = bch2_trans_run(c, bch2_btree_write_buffer_flush_locked(trans));
+	} while (!ret && bch2_btree_write_buffer_should_flush(c));
+	mutex_unlock(&wb->flushing.lock);
+
+	bch2_write_ref_put(c, BCH_WRITE_REF_btree_write_buffer);
+}
+
+int bch2_journal_key_to_wb_slowpath(struct bch_fs *c,
+			     struct journal_keys_to_wb *dst,
+			     enum btree_id btree, struct bkey_i *k)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+	int ret;
+retry:
+	ret = darray_make_room_gfp(&dst->wb->keys, 1, GFP_KERNEL);
+	if (!ret && dst->wb == &wb->flushing)
+		ret = darray_resize(&wb->sorted, wb->flushing.keys.size);
+
+	if (unlikely(ret)) {
+		if (dst->wb == &c->btree_write_buffer.flushing) {
+			mutex_unlock(&dst->wb->lock);
+			dst->wb = &c->btree_write_buffer.inc;
+			bch2_journal_pin_add(&c->journal, dst->seq, &dst->wb->pin,
+					     bch2_btree_write_buffer_journal_flush);
+			goto retry;
+		}
+
+		return ret;
+	}
+
+	dst->room = darray_room(dst->wb->keys);
+	if (dst->wb == &wb->flushing)
+		dst->room = min(dst->room, wb->sorted.size - wb->flushing.keys.nr);
+	BUG_ON(!dst->room);
+	BUG_ON(!dst->seq);
+
+	struct btree_write_buffered_key *wb_k = &darray_top(dst->wb->keys);
+	wb_k->journal_seq	= dst->seq;
+	wb_k->btree		= btree;
+	bkey_copy(&wb_k->k, k);
+	dst->wb->keys.nr++;
+	dst->room--;
+	return 0;
+}
+
+void bch2_journal_keys_to_write_buffer_start(struct bch_fs *c, struct journal_keys_to_wb *dst, u64 seq)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+
+	if (mutex_trylock(&wb->flushing.lock)) {
+		mutex_lock(&wb->inc.lock);
+		move_keys_from_inc_to_flushing(wb);
+
+		/*
+		 * Attempt to skip wb->inc, and add keys directly to
+		 * wb->flushing, saving us a copy later:
+		 */
+
+		if (!wb->inc.keys.nr) {
+			dst->wb = &wb->flushing;
+		} else {
+			mutex_unlock(&wb->flushing.lock);
+			dst->wb = &wb->inc;
+		}
+	} else {
+		mutex_lock(&wb->inc.lock);
+		dst->wb = &wb->inc;
+	}
+
+	dst->room = darray_room(dst->wb->keys);
+	if (dst->wb == &wb->flushing)
+		dst->room = min(dst->room, wb->sorted.size - wb->flushing.keys.nr);
+	dst->seq = seq;
+
+	bch2_journal_pin_add(&c->journal, seq, &dst->wb->pin,
+			     bch2_btree_write_buffer_journal_flush);
+}
+
+void bch2_journal_keys_to_write_buffer_end(struct bch_fs *c, struct journal_keys_to_wb *dst)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+
+	if (!dst->wb->keys.nr)
+		bch2_journal_pin_drop(&c->journal, &dst->wb->pin);
+
+	if (bch2_btree_write_buffer_should_flush(c) &&
+	    __bch2_write_ref_tryget(c, BCH_WRITE_REF_btree_write_buffer) &&
+	    !queue_work(system_unbound_wq, &c->btree_write_buffer.flush_work))
+		bch2_write_ref_put(c, BCH_WRITE_REF_btree_write_buffer);
+
+	if (dst->wb == &wb->flushing)
+		mutex_unlock(&wb->flushing.lock);
+	mutex_unlock(&wb->inc.lock);
+}
+
+static int bch2_journal_keys_to_write_buffer(struct bch_fs *c, struct journal_buf *buf)
+{
+	struct journal_keys_to_wb dst;
+	struct jset_entry *entry;
+	struct bkey_i *k;
+	int ret = 0;
+
+	bch2_journal_keys_to_write_buffer_start(c, &dst, le64_to_cpu(buf->data->seq));
+
+	for_each_jset_entry_type(entry, buf->data, BCH_JSET_ENTRY_write_buffer_keys) {
+		jset_entry_for_each_key(entry, k) {
+			ret = bch2_journal_key_to_wb(c, &dst, entry->btree_id, k);
+			if (ret)
+				goto out;
+		}
+
+		entry->type = BCH_JSET_ENTRY_btree_keys;
+	}
+
+	buf->need_flush_to_write_buffer = false;
+out:
+	bch2_journal_keys_to_write_buffer_end(c, &dst);
+	return ret;
+}
+
+static int wb_keys_resize(struct btree_write_buffer_keys *wb, size_t new_size)
+{
+	if (wb->keys.size >= new_size)
+		return 0;
+
+	if (!mutex_trylock(&wb->lock))
+		return -EINTR;
+
+	int ret = darray_resize(&wb->keys, new_size);
+	mutex_unlock(&wb->lock);
+	return ret;
+}
+
+int bch2_btree_write_buffer_resize(struct bch_fs *c, size_t new_size)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+
+	return wb_keys_resize(&wb->flushing, new_size) ?:
+		wb_keys_resize(&wb->inc, new_size);
+}
+
+void bch2_fs_btree_write_buffer_exit(struct bch_fs *c)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+
+	BUG_ON((wb->inc.keys.nr || wb->flushing.keys.nr) &&
+	       !bch2_journal_error(&c->journal));
+
+	darray_exit(&wb->sorted);
+	darray_exit(&wb->flushing.keys);
+	darray_exit(&wb->inc.keys);
+}
+
+int bch2_fs_btree_write_buffer_init(struct bch_fs *c)
+{
+	struct btree_write_buffer *wb = &c->btree_write_buffer;
+
+	mutex_init(&wb->inc.lock);
+	mutex_init(&wb->flushing.lock);
+	INIT_WORK(&wb->flush_work, bch2_btree_write_buffer_flush_work);
+
+	/* Will be resized by journal as needed: */
+	unsigned initial_size = 1 << 16;
+
+	return  darray_make_room(&wb->inc.keys, initial_size) ?:
+		darray_make_room(&wb->flushing.keys, initial_size) ?:
+		darray_make_room(&wb->sorted, initial_size);
+}