Re: 2.6.21-mm1: many processes end up in D state

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 30 Apr 2007 20:14:05 +0200
"Jiri Slaby" <jirislaby@gmail.com> wrote:

> > > I have a problem with higher disk loads (e.g. running git-log or yum update).
> > > Many processes end up in D state and system is unusable -- I'm not able to run
> > > anything but smooth mouse moving when this happens.
> > >
> > > If I wait for a 20-30sec it becomes usable. This happens in 2.6.21-rc7-mm2 and
> > > also in 2007-04-28-05-06 broken-out snapshot. I think 2.6.21-rc6-mm1 worked
> > > fine, but I'm uncertain. If it is important, let me know to re-test.
> > >
> >
> > It is important, but I doubt if retesting 2.6.21-rc6-mm1 will clarify
> > things a lot.
> >
> > Could you try switching to a different IO scheduler please?  Anticipatory
> > would suit.
> 
> As I wrote below the sysrq-t, switch to noop didn't help, but it seems
> that it's harder to reproduce with that:
> 
> <cite it's_bad_to_write_anything_below_logs="true">
> Note that yum works on lvm on raid0 and git too, but on the another md volume.
> Both ext3s. Drivers are sata_promise and ata_piix (sata disk); CFQ scheduler.
> Using noop is no change (but seems to be harder to reproduce with it). I figured
> out that it probably happens when 2+ processes are on both "processors" (HT on
> P4) and are IO wait (multiload-applet shows red above the half).
> 
> Swap usage is 0 all the time.
> </cite>

My comprehension skills on Monday morning are even less than usual ;)

I would check the anticipatory scheduler as well, please.  I don't know
what no-op would do with a workload like that, but it probably isn't very
good.

You appear to believe that it's related to the CPU scheduler?  That's a bit
unexpected - it sounds more like a VFS/IO thing?  But stranger things have
happened.

I guess it's time to end the staircase experiment in -mm. 
http://userweb.kernel.org/~akpm/js.bz2 is my current rollup (against
2.6.21) minus staircase and related things.  Pretty please.