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

Magnus Damm
2006-03-13T02:28:45Z

On 3/12/06, Peter Zijlstra <peter@programming.kicks-ass.net> wrote:
> 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.

Yes, you are explaining the current 2.6 behaviour much better. Also,
some balancing logic with nr_scan_active/nr_scan_inactive is present
in the code today. I'm not entirely sure about the purpose of that
code.

Thanks,

/ magnus