Re: [RFC] ext3: per-process soft-syncing data=ordered mode

[Jan Kara]

On Sat 26-01-08 08:27:43, Al Boldi wrote:
> Diego Calleja wrote:
> > El Thu, 24 Jan 2008 23:36:00 +0300, Al Boldi <a1426z@xxxxxxxxx> escribió:
> > > Greetings!
> > >
> > > data=ordered mode has proven reliable over the years, and it does this
> > > by ordering filedata flushes before metadata flushes.  But this
> > > sometimes causes contention in the order of a 10x slowdown for certain
> > > apps, either due to the misuse of fsync or due to inherent behaviour
> > > like db's, as well as inherent starvation issues exposed by the
> > > data=ordered mode.
> >
> > There's a related bug in bugzilla:
> > http://bugzilla.kernel.org/show_bug.cgi?id=9546
> >
> > The diagnostic from Jan Kara is different though, but I think it may be
> > the same problem...
> >
> > "One process does data-intensive load. Thus in the ordered mode the
> > transaction is tiny but has tons of data buffers attached. If commit
> > happens, it takes a long time to sync all the data before the commit
> > can proceed... In the writeback mode, we don't wait for data buffers, in
> > the journal mode amount of data to be written is really limited by the
> > maximum size of a transaction and so we write by much smaller chunks
> > and better latency is thus ensured."
> >
> >
> > I'm hitting this bug too...it's surprising that there's not many people
> > reporting more bugs about this, because it's really annoying.
> >
> >
> > There's a patch by Jan Kara (that I'm including here because bugzilla
> > didn't include it and took me a while to find it) which I don't know if
> > it's supposed to fix the problem , but it'd be interesting to try:
> 
> Thanks a lot, but it doesn't fix it.
  Hmm, if you're willing to test patches, then you could try a debug patch:
http://bugzilla.kernel.org/attachment.cgi?id=14574
  and send me the output. What kind of load do you observe problems with
and which problems exactly?

									Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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