On Tue, 1 Aug 2000, Rik van Riel wrote:
> >
> > Quite frankly, nobody has convinced me that there any way to fix VM
> > balancing issues even _if_ people were to re-write the VM.
>
> Nobody asks of you that you read all your email. However, I
> believe that most of the ideas for the new VM were CCd to
> you ;)
I've seen a lot of discussion, yes.
I haven't seen any really convining arguments that any of the rewrites
would really make things all that better.
Yes, they'll probably fix the thing that you try to fix. And they'll
introduce new cases where _they_ work badly, and the old code happened to
work fine.
For example, the "dd if=/dev/zero of=file" thing can be made to be very
nice on interactive behaviour, and you can obviously design a VM subsystem
that does that on purpose. Fine. I bet you that such a VM subsystem has
serious problems with some other workloads..
Or the old idea to start writebacks early in order to try to minimize
having dirty pages in memory that are hard to get rid of. It's wonderful.
For certain loads. And it really sucks on others that have big temp-files
that will get deleted (like bench).
The thing that is dangerous about designing a new VM is that you can
design it so that it avoids the current pitfalls. But you won't even be
aware of the things that the current thing does well, and you may not
design it to do as well on those.
And in the end, reality always tends to hit theory hard in the face when
you least expect it. That's why I'm not holding my breath for some magical
VM rewrite that will fix all performance problems. No matter _how_ much
people talk about it..
Linus
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This archive was generated by hypermail 2b29 : Mon Aug 07 2000 - 21:00:07 EST