bcachefs: Fragmentation LRU

Now that we have much more efficient updates to the LRU btree, this
patch adds a new LRU that indexes buckets by fragmentation.

This means copygc no longer has to scan every bucket to find buckets
that need to be evacuated.

Changes:
 - A new field in bch_alloc_v4, fragmentation_lru - this corresponds to
   the bucket's position in the fragmentation LRU. We add a new field
   for this instead of calculating it as needed because we may make the
   fragmentation LRU optional; this field indicates whether a bucket is
   on the fragmentation LRU.

   Also, zoned devices will introduce variable bucket sizes; explicitly
   recording the LRU position will be safer for them.

 - A new copygc path for using the fragmentation LRU instead of
   scanning every bucket and building up an in-memory heap.

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

1 files changed, 21 insertions, 0 deletions

diff --git a/fs/bcachefs/lru.h b/fs/bcachefs/lru.h
index b8d9848cdb1a..78a6076999ed 100644
--- a/fs/bcachefs/lru.h
+++ b/fs/bcachefs/lru.h
@@ -22,6 +22,27 @@ static inline u64 lru_pos_time(struct bpos pos)
 	return pos.inode & ~(~0ULL << LRU_TIME_BITS);
 }
 
+#define BCH_LRU_TYPES()		\
+	x(read)			\
+	x(fragmentation)
+
+enum bch_lru_type {
+#define x(n) BCH_LRU_##n,
+	BCH_LRU_TYPES()
+#undef x
+};
+
+#define BCH_LRU_FRAGMENTATION_START	((1U << 16) - 1)
+
+static inline enum bch_lru_type lru_type(struct bkey_s_c l)
+{
+	u16 lru_id = l.k->p.inode >> 48;
+
+	if (lru_id == BCH_LRU_FRAGMENTATION_START)
+		return BCH_LRU_fragmentation;
+	return BCH_LRU_read;
+}
+
 int bch2_lru_invalid(const struct bch_fs *, struct bkey_s_c, unsigned, struct printbuf *);
 void bch2_lru_to_text(struct printbuf *, struct bch_fs *, struct bkey_s_c);