bcachefs: Add a single slot percpu buf for btree iters

Allocating our array of btree iters is a big enough allocation that it
hits the buddy allocator, and we're seeing lots of lock contention.
Sticking a single element buffer in front of it should help.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 5 insertions, 0 deletions

diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index c14117227dd7..8ac96384fddf 100644
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -541,6 +541,10 @@ struct journal_keys {
 	u64			journal_seq_base;
 };
 
+struct btree_iter_buf {
+	struct btree_iter	*iter;
+};
+
 struct bch_fs {
 	struct closure		cl;
 
@@ -636,6 +640,7 @@ struct bch_fs {
 	struct mutex		btree_trans_lock;
 	struct list_head	btree_trans_list;
 	mempool_t		btree_iters_pool;
+	struct btree_iter_buf  __percpu	*btree_iters_bufs;
 
 	struct btree_key_cache	btree_key_cache;