Re: 2.6.14-rc2-mm1 - ext3 wedging up

[Andrea Arcangeli <andrea@suse.de>]

On Fri, Sep 23, 2005 at 03:20:33AM -0400, Valdis.Kletnieks@vt.edu wrote:
> On Fri, 23 Sep 2005 10:36:16 +1000, Con Kolivas said:
> 
> (Adding Andrea to the To: list...)
> 
> > On Fri, 23 Sep 2005 05:59, Valdis.Kletnieks@vt.edu wrote:
> > > Am seeing reproducible wedging up when writing large (20M+) files to an
> > > ext3 file system.  Oddly enough, if something *else* writes files to the
> > > file system as well, it will unwedge for a while and make progress.  Also,

So you get a total hang? I guess there's a bug somewhere...

> I'm pretty convinced that for this patch to work, it *will* need feedback from
> the actual (not max) disk bandwidth and possibly the actual amount of RAM -
> what works on Andrea's 1G workstation with (presumably) a real disk system
> is waay too much for 256M and a single laptop-class disk.

That's not the problem here if you get a total hang. This heuristic should
only reduce the amount of dirty memory, it should never grind a task 
to a total hang, until some other task writes to the filesystem.

The sysrq shows the task sleeping in blk_congestion_wait.

> For now, I'm leaving centisecs set to 40, and will see how that works - most
> of my "problem cases" involve an FTP on a 10/100mbit connection, so that will
> get tried tomorrow.....

You should leave it to 0 until I find the buglet that hangs the system.

I'll have a look.

One other thing to change is to call balance_dirty only when the dirty
bit is toggled (so overwrites of dirty cache are not accounted, since
they generate no additional I/O on disk).

Thanks.