4KSTACKS et al...

[Ian Kent]

On Thu, 4 Aug 2005, Paul wrote:

> On Thu, 2005-08-04 at 21:43 -0400, Dave Jones wrote:
> > On Fri, Aug 05, 2005 at 09:22:55AM +0800, Ian Kent wrote:
> >  > I also find it hard to understand why it is such a problem having a larger 
> >  > stack. As you point out, as software evolves it ultimately becomes more 
> >  > complex. If the developers design needs it and the software is reliable 
> >  > and efficient (aka performs well) then why not.
> >  > 
> >  > A quick caclulation.
> >  > 
> >  > 2000*4k is about 8M in say 1G at least.
> >  > 
> >  > Not a large percentage overhead I think.
> > 
> > Now try finding 2000 _contiguous_ pairs of pages after the machine
> > has been up for a while, under load.  Memory fragmentation makes
> > this a really nasty problem, and the VM eats its own head after
> > repeatedly scanning every page in the system.
> 
> I thought I heard that there was some work being done in the upstream
> kernel to have a process "defrag" memory in the background.  This would
> help alleviate this problem on systems with long up-times.

I'm afraid I have to agree with Dave on this.
Scanning pagelists really needs to be reduced to a minimum where ever 
possible.

Ian