bcachefs: Ensure journal reclaim runs when btree key cache is too dirty

Ensuring the key cache isn't too dirty is critical for ensuring that the
shrinker can reclaim memory.

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

1 files changed, 9 insertions, 0 deletions

diff --git a/fs/bcachefs/btree_key_cache.h b/fs/bcachefs/btree_key_cache.h
index e64a8e9c726f..7723a2178430 100644
--- a/fs/bcachefs/btree_key_cache.h
+++ b/fs/bcachefs/btree_key_cache.h
@@ -1,6 +1,15 @@
 #ifndef _BCACHEFS_BTREE_KEY_CACHE_H
 #define _BCACHEFS_BTREE_KEY_CACHE_H
 
+static inline size_t bch2_nr_btree_keys_need_flush(struct bch_fs *c)
+{
+	size_t nr_dirty = READ_ONCE(c->btree_key_cache.nr_dirty);
+	size_t nr_keys = READ_ONCE(c->btree_key_cache.nr_dirty);
+	size_t max_dirty = 1024 + (nr_keys * 3) / 4;
+
+	return max_t(ssize_t, 0, nr_dirty - max_dirty);
+}
+
 struct bkey_cached *
 bch2_btree_key_cache_find(struct bch_fs *, enum btree_id, struct bpos);