Btrfs: async delayed refs

Delayed extent operations are triggered during transaction commits.
The goal is to queue up a healthly batch of changes to the extent
allocation tree and run through them in bulk.

This farms them off to async helper threads.  The goal is to have the
bulk of the delayed operations being done in the background, but this is
also important to limit our stack footprint.

Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 16 insertions, 3 deletions

diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 3aafbde8b637..1c54e2eb74ab 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -697,6 +697,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 	unsigned long cur = trans->delayed_ref_updates;
 	int lock = (trans->type != TRANS_JOIN_NOLOCK);
 	int err = 0;
+	int must_run_delayed_refs = 0;
 
 	if (trans->use_count > 1) {
 		trans->use_count--;
@@ -711,10 +712,18 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 		btrfs_create_pending_block_groups(trans, root);
 
 	trans->delayed_ref_updates = 0;
-	if (!trans->sync && btrfs_should_throttle_delayed_refs(trans, root)) {
+	if (!trans->sync) {
+		must_run_delayed_refs =
+			btrfs_should_throttle_delayed_refs(trans, root);
 		cur = max_t(unsigned long, cur, 32);
-		trans->delayed_ref_updates = 0;
-		btrfs_run_delayed_refs(trans, root, cur);
+
+		/*
+		 * don't make the caller wait if they are from a NOLOCK
+		 * or ATTACH transaction, it will deadlock with commit
+		 */
+		if (must_run_delayed_refs == 1 &&
+		    (trans->type & (__TRANS_JOIN_NOLOCK | __TRANS_ATTACH)))
+			must_run_delayed_refs = 2;
 	}
 
 	if (trans->qgroup_reserved) {
@@ -775,6 +784,10 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans,
 	assert_qgroups_uptodate(trans);
 
 	kmem_cache_free(btrfs_trans_handle_cachep, trans);
+	if (must_run_delayed_refs) {
+		btrfs_async_run_delayed_refs(root, cur,
+					     must_run_delayed_refs == 1);
+	}
 	return err;
 }