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SubjectRe: VM Report was:Re: Break 2.4 VM in five easy steps
On Fri, 8 Jun 2001, John Stoffel wrote:

> Mike> OK, riddle me this. If this test is a crummy test, just how is
> Mike> it that I was able to warn Rik in advance that when 2.4.5 was
> Mike> released, he should expect complaints? How did I _know_ that?
> Mike> The answer is that I fiddle with Rik's code a lot, and I test
> Mike> with this test because it tells me a lot. It may not tell you
> Mike> anything, but it does me.
> I never said it was a crummy test, please do not read more into my
> words than was written. What I was trying to get across is that just
> one test (such as a compile of the kernel) isn't perfect at showing
> where the problems are with the VM sub-system.


Tobias> Could you please explain what is good about this test? I
Tobias> understand that it will stress the VM, but will it do so in a
Tobias> realistic and relevant way?

I agree, this isn't really a good test case. I'd rather see what
happens when you fire up a gimp session to edit an image which is
*almost* the size of RAM, or even just 50% the size of ram. Then how
does that affect your other processes that are running at the same

...but anyway, yes it just one test from any number of possibles.

> Jonathan Morton has been using another large compile to also test the
> sub-system, and it includes a compile which puts a large, single
> process pressure on the VM. I consider this to be a more
> representative test of how the VM deals with pressure.

What does 'more representative' mean given that the VM must react to
every situation it runs into?

> The kernel compile is an ok test of basic VM handling, but from what

Now we're communicating. I never said it was more than that ;-)

> I've been hearing on linux-kernel and linux-mm is that the VM goes to
> crap when you have a mix of stuff running, and one (or more) processes
> starts up or grows much larger and starts impacting the system
> performance.
> I'm also not knocking your contributions to this discussion, so stop
> being so touchy. I was trying to contribute and say (albeit poorly)
> that a *mix* of tests is needed to test the VM.

Yes, more people need to test. I don't need to do all of those other
tests (no have right toys), more people need to do repeatable tests.

> More importantly, a *repeatable* set of tests is what is needed to
> test the VM and get consistent results from run to run, so you can see
> how your changes are impacting performance. The kernel compile
> doesn't really have any one process grow to a large fraction of
> memory, so dropping in a compile which *does* is a good thing.

I know I'm only watching basic functionality. I'm watching basic
functionality with one very consistant test run very consistantly.


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