Re: [patch][rfc][rft] vm throughput 2.4.2-ac4

[Marcelo Tosatti]

On Wed, 28 Feb 2001, Mike Galbraith wrote:

> On Wed, 28 Feb 2001, Marcelo Tosatti wrote:
> 
> > On Wed, 28 Feb 2001, Mike Galbraith wrote:
> >
> > > > > Have you tried to use SWAP_SHIFT as 4 instead of 5 on a stock 2.4.2-ac5 to
> > > > > see if the system still swaps out too much?
> > > >
> > > > Not yet, but will do.
> >
> > But what about swapping behaviour?
> >
> > It still swaps too much?
> 
> Yes.
> 
> (returning to study mode)

Ok, I'm stupid. Changing SWAP_SHIFT will just balance the nr of tasks and
the per-task nr of scanned pte's, but the not (roughly) the total nr of
ptes scanned. I thought it would decrease the number of scanned ptes from
3% (which the current in -ac code does) to 0.3% (which Linus tree does) of
the total ptes.

The problem seems to be multiple users calling swap_out() with 3% of ptes
being scanned. This will unmap ptes way too heavily for common workloads.

Its magic number tuning.. but nothing better can be done for 2.4, I think.