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SubjectRe: VM in 2.4.7-pre hurts...

On Sat, 7 Jul 2001, Jeff Garzik wrote:
> Linus Torvalds wrote:
> >
> > Now, the fact that the system appears unusable does obviously mean that
> > something is wrong. But you're barking up the wrong tree.
>
> Two more additional data points,
>
> 1) partially kernel-unrelated. MDK's "make" macro didn't support
> alpha's /proc/cpuinfo output, "make -j$numprocs" became "make -j" and
> fun ensued.

Ahh, well..

The kernel source code is set up to scale quite well, so yes a "make -j"
will parallellise a bit teoo well for most machines, and you'll certainly
run out of memory on just about anything (I routinely get load averages of
30+, and yes, you need at least half a GB of RAM for it to not be
unpleasant - and probably more like a full gigabyte on an alpha).

So I definitely think the kernel likely did the right thing. It's not even
clear that the OOM killer might not have been right - due to the 2.4.x
swap space allocation, 256MB of swap-space is a bit tight on a 384MB
machine that actually wants to use a lot of memory.

> 2) I agree that 200MB into swap and 200MB into cache isn't bad per se,
> but when it triggers the OOM killer it is bad.

Note that it might easily have been 256MB into swap (ie it had eaten _all_
of your swap) at some stage - and you just didn't see it in the vmstat
output because obviously at that point the machine was a bit loaded.

But neutering the OOM killer like Alan suggested may be a rather valid
approach anyway. Delaying the killing sounds valid: if we're truly
livelocked on the VM, we'll be calling down to the OOM killer so much that
it's probably quite valid to say "only return 1 after X iterations".

Linus

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