Re: Page aging broken in 2.6

[Andrew Morton <akpm@osdl.org>]

Rik van Riel <riel@surriel.com> wrote:
>
> On Fri, 26 Dec 2003, Linus Torvalds wrote:
> 
> > I'll let Rik and Andrea argue that part - it's entirely possible that
> > getting lots of positive results is a _good_ thing, if the same page is
> > mapped multiple times. That would just make us less eager to unmap it,
> > which sounds like potentially the right thign to do (it's also how the
> > old non-rmap code worked, and I know Rik thought it was "unfair", but
> > whatever).
> 
> I'm really not sure which of the two behaviours would
> perform better.  Chances are both behaviours will show
> some performance improvement over the other, depending
> on the workload...
> 

The current behaviour seems better from a theoretical point of view.  All
we want to know is the reference pattern - whether it is one process
referencing the page frequently or 100 processes referencing it
infrequently shouldn't matter.  And if we want to give mapped pages more
preference over unmapped ones (they already have some preference, by the
default value of /proc/sys/vm/swappiness), we have less radical ways of
doing this.

But yes, it probably makes damn-all difference across a mix of workloads.