Re: 2.6.0-test9 - poor swap performance on low end machines

Andrea Arcangeli
2003-12-10T22:43:09Z

On Wed, Dec 10, 2003 at 11:05:25PM +0100, Roger Luethi wrote:
> On Wed, 10 Dec 2003 22:52:35 +0100, Andrea Arcangeli wrote:
> > On Mon, Dec 08, 2003 at 12:48:17PM -0800, William Lee Irwin III wrote:
> > > qsbench I'd pretty much ignore except as a control case, since there's
> > > nothing to do with a single process but let it thrash.
> >
> > this is not the point. If a single process like qsbench trashes twice as
> > fast in 2.4, it means 2.6 has some great problem in the core vm, the
> > whole point of swap is to trash but to give the task more physical
> > virtual memory. I doubt you can solve it with anything returned by
> > si_swapinfo.
>
> Uhm.. guys? I forgot to mention that earlier: qsbench as I used it was not
> about one single process. There were four worker processes (-p 4), and my
> load control stuff did make it run faster, so the point is moot.

more processes can be optimized even better by adding unfariness.
Either ways a significant slowdown of qsbench probably means worse core
VM, at least if compared with 2.4 that isn't adding huge unfariness just
to optimize qsbench.

> Also, the 2.6 core VM doesn't seem all that bad since it was introduced in
> 2.5.27 but most of the problems I measured were introduced after 2.5.40.
> Check out the graph I posted.

you're confusing rmap with core vm. rmap in no way can be defined as the
core vm, rmap is just a method used by the core vm to find some
information more efficiently at the expenses of all the fast paths
that now have to do the rmap bookkeeping.