On Fri, Jan 21, 2011 at 12:13:02AM +0000, Jon Leighton wrote: > Hi there, > > I have been experiencing some slowness with an ext4 filesystem. I will > try to explain and hopefully somebody can identify whether this is > "normal" or not. Sorry if I am in any sense unscientific - filesystems > are somewhere near the edge of my computer science knowledge :) > > Basically I am involved with doing some development on the Ruby on Rails > web app framework, and the automated tests for one component (Active > Record) does a lot of reading/writing from a database. > > I realised that the test suite was running significantly slower for me > than for another developer, so I started to investigate. First I created > an unencrypted partition and put my databases on it, as I had previously > had everything encrypted. > > This made it somewhat faster, but not massively. > > I then used iotop to see what was going on when I ran the tests. I > discovered that the process jbd2/sda3-8 was doing *lots* of IO when I > run these tests. > > I did some googling and tried a few things. Removing the journal solved > the problem (as would be expected, I guess), but also recreating the > partition as ext3 rather than ext4 solved it too (which perhaps > indicates a regression?) When I say 'solved', I mean it took a single > run of this particular test suite from say 4.5 minutes to more like > 60-80 seconds. > > I found some other people reporting a similar problem: > https://bugs.launchpad.net/ubuntu/+source/linux/+bug/607560 > > They complain of the jbd2 process running every few seconds. This is > something I had not noticed before, but I can observe this on my system > too. It runs and uses a lot of IO for a short period of time maybe every > 2 seconds. So I think I am experiencing the same problem. > > FWIW, using the noatime option does not help at all. Also, I have tried > using a very recent kernel build with no success. And I have run iotop > on another laptop (which also has an ext4 partition) and I cannot > observe this frequent running of jbd2. > > So: does this sound like a bug, and if so, what can be done? I'm very > happy to provide any additional information as needed. > What kind of database is this? Does it use lots of files? When it's being particularly slow could you run echo w > /proc/sysrq-trigger a couple of times, spread out. This will give us an idea of what everybody is doing when things are going slow. Thanks, Josef -- 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
