Re: multi-second freezes with current GIT?

[David Miller <davem@davemloft.net>]

From: Mike Galbraith <efault@gmx.de>
Date: Wed, 09 May 2007 05:29:20 +0200

> On Tue, 2007-05-08 at 18:44 -0700, David Miller wrote:
> > I've been noticing this off and on for the past week or so.
> > 
> > The system seems to jam up for several seconds, anything that would
> > need to read from disk just sits there during this time.  I think it's
> > correlated with generating a lot of dirty write data.
> > 
> > My mouse moves around in X etc. so it really is only processes that
> > need to read from disk that get stuck.
> > 
> > Perhaps it's a side effect of those dirty ratio changes Linus made to
> > start off the 2.6.22 merge cycle?
> 
> Uhoh, that seems highly likely.
> 
> I think those changes may have been triggered by my repeatable and truly
> horrible system stalls when writing to an ext3 data=ordered nearly full
> filesystem.  Anything that does fdatasync() and/or fsync() can cause
> very bad experiences indeed.  KDE's little menu/program launcher
> doohickey does fdatasync() for some odd reason, which has utterly killed
> my entire GUI for up to and including 20 minutes at a whack.
> 
> Switching to data=writeback cured those horrors.  Lowering the dirty
> ratio reduced the agony of data=ordered tremendously, but didn't make it
> even remotely acceptable.

I'm using data=ordered on my partitions too.