Re: [RFC] Optimization for use-once pages

[Daniel Phillips]

On Tuesday 24 July 2001 22:53, Marcelo Tosatti wrote:
> On Tue, 24 Jul 2001, Rik van Riel wrote:
> > On Tue, 24 Jul 2001, Marcelo Tosatti wrote:
> > > On Tue, 24 Jul 2001, Daniel Phillips wrote:
> > > > Today's patch tackles the use-once problem, that is, the
> > > > problem of
> > >
> > > Well, as I see the patch should remove the problem where
> > > drop_behind() deactivates pages of a readahead window even if
> > > some of those pages are not "used-once" pages, right ?
> > >
> > > I just want to make sure the performance improvements you're
> > > seeing caused by the fix of this _particular_ problem.
> >
> > Fully agreed.
> >
> > Especially since it was a one-liner change from worse
> > performance to better performance (IIRC) it would be
> > nice to see exactly WHY the system behaves the way it
> > does.  ;)
>
> Yes.
>
> Daniel's patch adds "drop behind" (that is, adding swapcache
> pages to the inactive dirty) behaviour to swapcache pages.
>
> This is a _new_ thing, and I would like to know how that is changing
> the whole VM behaviour..

Yes, absolutely.  I knew I was doing that but I also thought it wouldn't
hurt.  Rather it's part of a transition towards a full unification of 
the file and swap paths.

Basically, I just left that part of it hanging.  If you check my 
detailed timings you'll see all my test runs have swaps=0, basically
because I didn't really want to hear about it just then ;-)

I was pretty sure it could be fixed if it broke.

--
Daniel