Re: 1352 NUL bytes at the end of a page? (was Re: Assertion `s && s->tree' failed: The saga continues.)

Steven Cole
2004-05-17T02:13:33Z

On Sunday 16 May 2004 05:53 pm, Andrea Arcangeli wrote:
> On Sun, May 16, 2004 at 04:11:16PM -0600, Steven Cole wrote:
> > On Sunday 16 May 2004 03:29 pm, Andrew Morton wrote:
> > > Steven Cole <elenstev@mesatop.com> wrote:
> > > >
> > > > Anyway, although the regression for my particular machine for this
> > > > particular load may be interesting, the good news is that I've seen
> > > > none of the failures which started this whole thread, which are relatively
> > > > easily reproduceable with PREEMPT set.
> > >
> > > So... would it be correct to say that with CONFIG_PREEMPT, ppp or its
> > > underlying driver stack
> > >
> > > a) screws up the connection and hangs and
> > >
> > > b) scribbles on pagecache?
> > >
> > > Because if so, the same will probably happen on SMP.
> > >
> > Perhaps someone has the hardware to test this.
> >
> > To summarize my experience with the past 24 hours of testing:
> > Without PREEMPT , everything is rock solid.
>
> so we've two separate problems: the first is the ppp instability with
> preempt, the second is a regresion in the vm heuristics between 2.6.3
> and 2.6.5.
Yes, that is correct.
The instability was first noticed about one month ago when doing
a bk pull from linus' repository. I've been updating my kernel via
bk almost nightly, and around the time of 2.6.6-rc1 (IIRC), I got the
Assertion `s && s->tree' failed message from bk. At first it was thought
to be related to using an older version (3.0.1) of bk, so that was updated.
A few days later, the problem recurred. Since it only happened about
15% to 20% of the time, and was easy to recover from, I didn't scream
too loudly or too often to bitmover. But then, the problem started becoming
more persistent about a week ago, so I began complaining again. I managed
to get a bitkeeper-generated file to bitmover, who discovered that a very
odd (or even in this case) number of NUL bytes existed where they
should not exist. Hence this thread.

Then during the course of testing, I noticed the significant difference
in time it took to run a test script supplied by bitkeeper for current kernels
versus an older vendor kernel. Hence your being cc'ed.

>
> > and I (cringes at the thought) may repeat some bk pulls with
> > PREEMPT set.
>
> I've heard other reports of preempt being unstable with some sound
> stuff, just in case are you using sound drivers at all during that
> workload?
>
>
Yes, mea culpa. CONFIG_SND_ENS1371=y.

Steven