Re: [rfc][patch 1/2] mm: dont account ZERO_PAGE

Nick Piggin
2007-03-30T03:09:12Z

On Thu, Mar 29, 2007 at 09:59:37PM -0500, Robin Holt wrote:
> On Fri, Mar 30, 2007 at 03:46:34AM +0200, Nick Piggin wrote:
> > > Oh, it's easy to devise a test-case of that kind, but does it matter
> > > in real life? I admit that what most people run on their 1024-core
> > > Altices will be significantly different from what I checked on my
> > > laptop back then, but in my case use of the ZERO_PAGE didn't look
> > > common enough to make special cases for.
> >
> > Yeah I don't have access to the box, but it was a constructed test
> > of some kind. However this is basically a dead box situation... on
> > smaller systems we could still see performance improvements.
>
> It was not a constructed test. It was an test application which started
> up and read one word from each page to fill the page tables (not sure
> why that was done), then forked a process for each cpu. At that point,
> it was supposed start doing computation using data from an NFS accessible
> file. Unfortunately, the file was not found so the application exited
> and the machine locked up for hours.

Sorry, my mistake. Thanks for the clarification: this sounds like
something that will not be helped by per-node ZERO_PAGEs either.

So not typical, but something that we'd rather not fall over with.
I guess large ranges of zero pages could be quite common in startup
of HPC codes operating on large matricies.

Thanks,
Nick