Theodore Ts'o wrote:
As I mentioned on the ext4 call yesterday, there was an interesting thread on LKML that wasn't cc'ed onto the linux-ext4 mailing list. So in case folks missed it, it might be worth taking a look at this mail thread: [PATCH] Give kjournald a IOPRIO_CLASS_RT io priority http://lkml.org/lkml/2008/10/1/405 The main issue that got discussed was the age-old "entaglement" problem. The jbd/jbd2 layer is supposed to avoid this by not blocking the "current" transaction why the blocks from the previous "committing" transaction are still being written out to disk. Apparently this was broken sometime in the 2.5 time-frame: http://lkml.org/lkml/2008/10/2/41 http://lkml.org/lkml/2008/10/2/322 Later in the thread, a major contention point in do_get_write_access() was identified as the problem: http://lkml.org/lkml/2008/10/3/7 ... and then andrew produced the following "hacky" fix: http://lkml.org/lkml/2008/10/3/22 If someone has time to runs some benchmarks to see how this improves things, especially on a workload that has plenty of "engtanglements", that would be great. (I bet Ric's fs_mark run should do a good job; fsyncs to creates lots of commits and the need to modify blocks that had been modified in the previous tansactions.) If we can get some quick testing done, and it shows really good results, this could be something that could try fast-tracking into the 2.6.28 merge window. - Ted
We are going to try and poke at this - do you suspect a single or multi-threaded test would work best?
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