Re: [PATCH 00/03] Unmapped: Separate unmapped and mapped pages

Peter Zijlstra
2006-03-11T20:58:14Z

On Fri, 2006-03-10 at 14:19 +0100, Magnus Damm wrote:
> On 3/10/06, Arjan van de Ven <arjan@infradead.org> wrote:
> > > Apply on top of 2.6.16-rc5.
> > >
> > > Comments?
> >
> >
> > my big worry with a split LRU is: how do you keep fairness and balance
> > between those LRUs? This is one of the things that made the 2.4 VM suck
> > really badly, so I really wouldn't want this bad...
>
> Yeah, I agree this is important. I think linux-2.4 tried to keep the
> LRU list lengths in a certain way (maybe 2/3 of all pages active, 1/3
> inactive). In 2.6 there is no such thing, instead the number of pages
> scanned is related to the current scanning priority.

This sounds wrong, the active and inactive lists are balanced to a 1:1
ratio. This is happens because the scan speed is directly proportional
to the size of the list. Hence the largest list will shrink fastest -
this gives a natural balance to equal sizes.

Peter