bcachefs: Fix btree key cache dirty checks

Had a type that meant we were triggering journal reclaim _much_ more
aggressively than needed. Also, fix a potential integer overflow.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/btree_key_cache.h

@@ -4,8 +4,8 @@
 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 = 4096 + nr_keys  / 2;
+	size_t nr_keys = READ_ONCE(c->btree_key_cache.nr_keys);
+	size_t max_dirty = 1024 + nr_keys  / 2;
 
 	return max_t(ssize_t, 0, nr_dirty - max_dirty);
 }
@@ -13,7 +13,7 @@ static inline size_t bch2_nr_btree_keys_need_flush(struct bch_fs *c)
 static inline bool bch2_btree_key_cache_must_wait(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 nr_keys = READ_ONCE(c->btree_key_cache.nr_keys);
 	size_t max_dirty = 4096 + (nr_keys * 3) / 4;
 
 	return nr_dirty > max_dirty;

fs/bcachefs/journal_reclaim.c

@@ -240,6 +240,7 @@ void bch2_journal_space_available(struct journal *j)
 	u64s_remaining -= (u64) total << 3;
 	u64s_remaining = max(0LL, u64s_remaining);
 	u64s_remaining /= 2;
+	u64s_remaining = min_t(u64, u64s_remaining, U32_MAX);
 out:
 	j->cur_entry_sectors	= !ret ? j->space[journal_space_discarded].next_entry : 0;
 	j->cur_entry_error	= ret;