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

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Date:	Sat, 26 Jan 2008 08:27:43 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Diego Calleja <diegocg@...il.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jan Kara <jack@...e.cz>
Subject: Re: [RFC] ext3: per-process soft-syncing data=ordered mode

Diego Calleja wrote:
> El Thu, 24 Jan 2008 23:36:00 +0300, Al Boldi <a1426z@...ab.com> 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.

--
Al

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