bcachefs: btree key cache pcpu freedlist

Originally, the btree key cache code would always allocate new entries
by reusing from the recently-freed list, if that list wasn't empty. But
that behaviour was dropped, for lock contention reasons.

But it seems that entries stranded on the freed list have been
contributing to some of our oom issues, because long running btree
transactions will prevent them from being freed.

This patch re-adds allocating from the freed list, but it also adds
percpu buffers to solve the lock contention issues - and the new percpu
freed lists will improve the evict paths, too.

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

1 files changed, 7 insertions, 1 deletions

diff --git a/fs/bcachefs/btree_types.h b/fs/bcachefs/btree_types.h
index 4f3e1086a86b..2eb8cc11aec4 100644
--- a/fs/bcachefs/btree_types.h
+++ b/fs/bcachefs/btree_types.h
@@ -298,6 +298,11 @@ struct btree_iter {
 	struct bpos		journal_pos;
 };
 
+struct btree_key_cache_freelist {
+	struct bkey_cached	*objs[16];
+	unsigned		nr;
+};
+
 struct btree_key_cache {
 	struct mutex		lock;
 	struct rhashtable	table;
@@ -305,8 +310,9 @@ struct btree_key_cache {
 	struct list_head	freed;
 	struct shrinker		shrink;
 	unsigned		shrink_iter;
+	struct btree_key_cache_freelist __percpu *pcpu_freed;
 
-	size_t			nr_freed;
+	atomic_long_t		nr_freed;
 	atomic_long_t		nr_keys;
 	atomic_long_t		nr_dirty;
 };