Re: Kernel 2.6.8.1: swap storm of death - CFQ scheduler=culprit

Jens Axboe
2004-08-24T10:54:21Z

On Tue, Aug 24 2004, Marcelo Tosatti wrote:
> On Tue, Aug 24, 2004 at 12:03:43PM +0200, Jens Axboe wrote:
> > On Mon, Aug 23 2004, Karl Vogel wrote:
> > > > > Jens, is this huge amount of bio/biovec's allocations
> > > > expected with CFQ? Its really really bad.
> > > >
> > > > Nope, it's not by design :-)
> > > >
> > > > A test case would be nice, then I'll fix it as soon as possible. But
> > > > please retest with 2.6.8.1 marcelo, 2.6.8-rc4 is missing an important
> > > > fix to ll_rw_blk that can easily cause this. The first report is for
> > > > 2.6.8.1, so I'm more puzzled on that.
> > >
> > > I tried with 2.6.8.1 and 2.6.8.1-mm4, both had the problem. If there
> > > is anything extra I need to try/record, just shoot!
> > >
> > > Original post with testcase + stats:
> > > http://article.gmane.org/gmane.linux.kernel/228156
> >
> > 2.6.8.1-mm4 clean does not reproduce the problem. Marcelo, your
> > 2.6.8-rc4 report is not valid due to the fixed problem related to that
> > in CFQ already. I'd still like for you to retest with 2.6.8.1.
> >
> > So I'm trying 2.6.8.1 with voluntary preempt applied now, the bug could
> > be related to that.
>
> Jens,
>
> You are right, I've been unable to reproduce the problem I was seeing
> (huge amount of bio/biovec's allocation causing major swapouts) with
> 2.6.8.1.
>
> With this kernel, The 512MB system swaps around 50MB and recovers perfectly,
> I can't see any odd behaviour with CFQ.

Great, thanks for verifying. So that just leaves this other problem,
once traces of hung processes are generated we'll know more. Currently I
cannot reproduce it with 2.6.8.1-mm4 at all, enabling preempt did
nothing to help it.

--
Jens Axboe