bcachefs: Add an option for whether inodes use the key cache

We probably don't ever want to flip this off in production, but it may
be useful for certain kinds of testing.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/bcachefs_format.h

@@ -1350,6 +1350,7 @@ LE64_BITMASK(BCH_SB_GC_RESERVE_BYTES,	struct bch_sb, flags[2],  4, 64);
 LE64_BITMASK(BCH_SB_ERASURE_CODE,	struct bch_sb, flags[3],  0, 16);
 LE64_BITMASK(BCH_SB_METADATA_TARGET,	struct bch_sb, flags[3], 16, 28);
 LE64_BITMASK(BCH_SB_SHARD_INUMS,	struct bch_sb, flags[3], 28, 29);
+LE64_BITMASK(BCH_SB_INODES_USE_KEY_CACHE,struct bch_sb, flags[3], 29, 30);
 
 /*
  * Features:

fs/bcachefs/inode.c

@@ -300,8 +300,10 @@ struct btree_iter *bch2_inode_peek(struct btree_trans *trans,
 	struct bkey_s_c k;
 	int ret;
 
-	iter = bch2_trans_get_iter(trans, BTREE_ID_inodes, POS(0, inum),
-				   BTREE_ITER_CACHED|flags);
+	if (trans->c->opts.inodes_use_key_cache)
+		flags |= BTREE_ITER_CACHED;
+
+	iter = bch2_trans_get_iter(trans, BTREE_ID_inodes, POS(0, inum), flags);
 	k = bch2_btree_iter_peek_slot(iter);
 	ret = bkey_err(k);
 	if (ret)
@@ -577,8 +579,12 @@ int bch2_inode_rm(struct bch_fs *c, u64 inode_nr, bool cached)
 	struct bpos end = POS(inode_nr + 1, 0);
 	struct bch_inode_unpacked inode_u;
 	struct bkey_s_c k;
+	unsigned iter_flags = BTREE_ITER_INTENT;
 	int ret;
 
+	if (cached && c->opts.inodes_use_key_cache)
+		iter_flags |= BTREE_ITER_CACHED;
+
 	bch2_trans_init(&trans, c, 0, 1024);
 
 	/*
@@ -600,11 +606,8 @@ int bch2_inode_rm(struct bch_fs *c, u64 inode_nr, bool cached)
 retry:
 	bch2_trans_begin(&trans);
 
-	iter = bch2_trans_get_iter(&trans, BTREE_ID_inodes, POS(0, inode_nr),
-				   (cached
-				    ? BTREE_ITER_CACHED
-				    : BTREE_ITER_SLOTS)|
-				   BTREE_ITER_INTENT);
+	iter = bch2_trans_get_iter(&trans, BTREE_ID_inodes,
+				   POS(0, inode_nr), iter_flags);
 	k = bch2_btree_iter_peek_slot(iter);
 
 	ret = bkey_err(k);

fs/bcachefs/opts.h

@@ -173,6 +173,11 @@ enum opt_type {
 	  OPT_BOOL(),							\
 	  BCH_SB_SHARD_INUMS,		false,				\
 	  NULL,		"Shard new inode numbers by CPU id")		\
+	x(inodes_use_key_cache,	u8,					\
+	  OPT_FORMAT|OPT_MOUNT,						\
+	  OPT_BOOL(),							\
+	  BCH_SB_INODES_USE_KEY_CACHE,	true,				\
+	  NULL,		"Use the btree key cache for the inodes btree")	\
 	x(gc_reserve_percent,		u8,				\
 	  OPT_FORMAT|OPT_MOUNT|OPT_RUNTIME,				\
 	  OPT_UINT(5, 21),						\