Re: it keeps crashing
On Sun, Jul 22, 2001 at 10:12:15AM -0400, Brian Nelson wrote:
> On Sat, Jul 21, 2001 at 11:30:31AM +0200, Martin F. Krafft wrote:
> > also sprach Joost Kooij (on Sat, 21 Jul 2001 11:00:52AM +0200):
> > > As to why Martin is having crashes, I don't know. Try it with a
> > > smaller kernel image size, as Guy suggests, by leaving out options
> > > that you do not strictly need. Also be sure to use the latest
> > > available 2.2.x or 2.4.x kernel and if the crashes persist, read
> > > the ksymoops documentation and the linux-kernel mailing list faq,
> > > and post a decoded oops on that list.
> >
> > that's a good idea. other than that, the kernel is 2.4.6 and already
> > only 300kb -- and i load 7 modules. it's cut down as far as possible.
> >
> > i am thinking that the swap implementation in linux is buggy. wouldn't
> > surprise me, after all, it wasn't chuck cranor's work :)
> >
> > martin; (greetings from the heart of the sun.)
> > \____ echo mailto: !#^."<*>"|tr "<*> mailto:"; net@madduck
>
> The Linux kernel's swap implementation is notoriously buggy, and I
> think 2.4.x is especially bad. I think you may have way too much swap
> space. Try a small value, like 12 megs or so. You might run out of
> memory when running userland apps, but it may keep the kernel from
> crashing.
Check that. From the June 7, 2001 LWN:
About that swapping problem. Problems with the use of swap space in
2.4.x were also mentioned last week. The amount of complaining has
gone up recently, as more people try out the 2.4.5 kernel, which
appears to be worse.
The response from the kernel hackers so far has been "make sure your
swap area is at least twice as large as the amount of RAM in the
system." That allows the kernel, essentially, to waste half of the
swap space as a copy of what is currently in RAM, and actually swap to
the other half. That technique helps, but a number of people are, not
surprisingly, unimpressed with that requirement. 2.2 systems seemed to
work better, after all. In fact, 2.2 had the same problem with
swapping, but the more aggressive approach to caching in 2.4 has made
the problem bite a lot more people.
And from the LWN a week earlier:
Stabilizing memory performance in 2.4. One of the remaining problem
areas in the 2.4 kernel is its virtual memory subsystem. Not only are
there simple performance problems, but there are also still situations
that can cause the kernel to deadlock. Not quite what one wants to see
in a stable series. The kernel hackers are working on dealing with
these problems, however; with luck, VM difficulties will not be with
us for much longer.
One problem that users of recent 2.4 kernels are likely to have
noticed is heavy use of swap space. It is not unusual for a kernel to
be running heavily in swap even when there is not that much going on
with the system. This problem seems to have only gotten worse with
recent kernels. It is, of course, the same old bug where the kernel
fails to recover swap space for pages which have been brought back
into memory (covered in the May 3 kernel page). This problem will get
fixed, but not quite yet. Alan Cox phrased it well:
That is a giant size special edition stupid design flaw that is on the
VM hackers list. But there are only a finite number of patches you can
do in a day, and things like sucking completely came first I believe.
Alan didn't spell out what "sucking completely" meant, but most would
probably agree that system deadlocks could be fairly described with
that term. Rik van Riel this week managed to stir things up a bit with
this patch which attempted to fix a couple of deadlock problems.
--
Brian Nelson <nelson@bignachos.com>
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