bcachefs: Add an option for metadata_target

Also, make journal writes obey foreground_target and metadata_target.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/bcachefs_format.h

@@ -1309,6 +1309,7 @@ LE64_BITMASK(BCH_SB_BACKGROUND_COMPRESSION_TYPE,
 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);
 
 /*
  * Features:

fs/bcachefs/btree_update_interior.c

@@ -222,7 +222,10 @@ static struct btree *__bch2_btree_node_alloc(struct bch_fs *c,
 	mutex_unlock(&c->btree_reserve_cache_lock);
 
 retry:
-	wp = bch2_alloc_sectors_start(c, c->opts.foreground_target, 0,
+	wp = bch2_alloc_sectors_start(c,
+				      c->opts.metadata_target ?:
+				      c->opts.foreground_target,
+				      0,
 				      writepoint_ptr(&c->btree_write_point),
 				      &devs_have,
 				      res->nr_replicas,

fs/bcachefs/journal_io.c

@@ -5,6 +5,7 @@
 #include "btree_update_interior.h"
 #include "buckets.h"
 #include "checksum.h"
+#include "disk_groups.h"
 #include "error.h"
 #include "io.h"
 #include "journal.h"
@@ -1031,16 +1032,20 @@ static int journal_write_alloc(struct journal *j, struct journal_buf *w,
 			       unsigned sectors)
 {
 	struct bch_fs *c = container_of(j, struct bch_fs, journal);
+	struct bch_devs_mask devs;
 	struct journal_device *ja;
 	struct bch_dev *ca;
 	struct dev_alloc_list devs_sorted;
+	unsigned target = c->opts.metadata_target ?:
+		c->opts.foreground_target;
 	unsigned i, replicas = 0, replicas_want =
 		READ_ONCE(c->opts.metadata_replicas);
 
 	rcu_read_lock();
+retry:
+	devs = target_rw_devs(c, BCH_DATA_journal, target);
 
-	devs_sorted = bch2_dev_alloc_list(c, &j->wp.stripe,
-					  &c->rw_devs[BCH_DATA_journal]);
+	devs_sorted = bch2_dev_alloc_list(c, &j->wp.stripe, &devs);
 
 	__journal_write_alloc(j, w, &devs_sorted,
 			      sectors, &replicas, replicas_want);
@@ -1072,6 +1077,12 @@ static int journal_write_alloc(struct journal *j, struct journal_buf *w,
 
 	__journal_write_alloc(j, w, &devs_sorted,
 			      sectors, &replicas, replicas_want);
+
+	if (replicas < replicas_want && target) {
+		/* Retry from all devices: */
+		target = 0;
+		goto retry;
+	}
 done:
 	rcu_read_unlock();
 

fs/bcachefs/opts.h

@@ -136,6 +136,11 @@ enum opt_type {
 	  OPT_STR(bch2_str_hash_types),					\
 	  BCH_SB_STR_HASH_TYPE,		BCH_STR_HASH_OPT_SIPHASH,	\
 	  NULL,		"Hash function for directory entries and xattrs")\
+	x(metadata_target,		u16,				\
+	  OPT_FORMAT|OPT_MOUNT|OPT_RUNTIME|OPT_INODE,			\
+	  OPT_FN(bch2_opt_target),					\
+	  BCH_SB_METADATA_TARGET,	0,				\
+	  "(target)",	"Device or disk group for metadata writes")	\
 	x(foreground_target,		u16,				\
 	  OPT_FORMAT|OPT_MOUNT|OPT_RUNTIME|OPT_INODE,			\
 	  OPT_FN(bch2_opt_target),					\