[Btrfs-devel] [RFC] wait for more writers to join the transaction

[Josef Bacik]

Hello,

Sorry for my long silence, getting all situated took longer than I expected.  I
just wrote something very quickly to try and make btrfs sleep longer if there
were writers while we were sleeping during an fsync.  Running the fs_mark test,
btrfs by itself gets walloped by ext3, so I'm ignoring that for now.  With
btrfs+my patch we seem to get about the same performance, except in the -S2 and
-S5 cases, which are

 Sync method: SYSTEM SYNC/SINGLE FSYNC: Issue sync() after main write loop and 1
file fsync() per subdirectory

Sync method: POST: Reopen and fsync() each file in order after main write loop

Now I don't think thats good enough so this is going to require more work, but
I'm also kind of new to journalling stuff so I wanted to run this by people to
see if I'm going in the right direction.  Might as well get put on the right
track before I go hacking around at things.  Thank you,

Josef

diff -r 1765acb6d268 transaction.c
--- a/transaction.c	Tue Aug 07 16:35:25 2007 -0400
+++ b/transaction.c	Tue Aug 07 17:29:12 2007 -0400
@@ -56,6 +56,7 @@ static int join_transaction(struct btrfs
 		root->fs_info->generation++;
 		root->fs_info->running_transaction = cur_trans;
 		cur_trans->num_writers = 0;
+		cur_trans->writers_while_asleep = 0;
 		cur_trans->transid = root->fs_info->generation;
 		init_waitqueue_head(&cur_trans->writer_wait);
 		init_waitqueue_head(&cur_trans->commit_wait);
@@ -67,6 +68,7 @@ static int join_transaction(struct btrfs
 		init_bit_radix(&cur_trans->dirty_pages);
 	}
 	cur_trans->num_writers++;
+	cur_trans->writers_while_asleep++;
 	return 0;
 }
 
@@ -454,12 +456,16 @@ int btrfs_commit_transaction(struct btrf
 			mutex_lock(&root->fs_info->trans_mutex);
 		}
 	}
-	while (trans->transaction->num_writers > 1) {
+	while (trans->transaction->num_writers > 1 ||
+		trans->transaction->writers_while_asleep > 0) {
+
 		WARN_ON(cur_trans != trans->transaction);
+		
 		prepare_to_wait(&trans->transaction->writer_wait, &wait,
 				TASK_UNINTERRUPTIBLE);
 		if (trans->transaction->num_writers <= 1)
 			break;
+		trans->transaction->writers_while_asleep = 0;
 		mutex_unlock(&root->fs_info->fs_mutex);
 		mutex_unlock(&root->fs_info->trans_mutex);
 		schedule();
diff -r 1765acb6d268 transaction.h
--- a/transaction.h	Tue Aug 07 16:35:25 2007 -0400
+++ b/transaction.h	Tue Aug 07 17:23:30 2007 -0400
@@ -26,6 +26,7 @@ struct btrfs_transaction {
 	int in_commit;
 	int use_count;
 	int commit_done;
+	unsigned long writers_while_asleep;
 	struct list_head list;
 	struct radix_tree_root dirty_pages;
 	unsigned long start_time;