On Fri 27-03-09 17:03:38, Chris Mason wrote: > On Fri, 2009-03-27 at 16:50 -0400, Chris Mason wrote: > > On Fri, 2009-03-27 at 16:24 -0400, Theodore Ts'o wrote: > > > The following patches have been posted as providing at least some > > > partial improvement to the ext3 latency problem that has been > > > discussed on the 2.6.29 mongo-LKML-thread-that-would-not-die. > > > > Ric had asked me about a test program that would show the worst case > > ext3 behavior. So I've modified your ext3 program a little. It now > > creates a 8G file and forks off another proc to do random IO to that > > file. > > > > Then it runs one fsync every 4 seconds and times how long they take. > > After the program has been running for 60 seconds, it tries to stop. > > > > On my sata drive with barriers on, even btrfs and xfs saw some > > multi-second fsyncs, but ext3 came in at 414s for a single fsync. > > > > Warning: don't run this on a laptop drive, you'll still be waiting for > > it next year. This is probably full of little errors, I cut it together > > pretty quickly. > > > > My understanding of ext4 delalloc is that once blocks are allocated to > file, we go back to data=ordered. Yes. > Ext4 is going pretty slowly for this fsync test (slower than ext3), it > looks like we're going for a very long time in > jbd2_journal_commit_transaction -> write_cache_pages. Yes, this is how we writeout ordered data and obviously it takes long for such a huge file where you do random IO... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
