Re: [PATCH 6/9] clockpro-clockpro.patch

[Marcelo Tosatti <marcelo.tosatti@cyclades.com>]

Hi Rik!

On Fri, Dec 30, 2005 at 08:22:12PM -0500, Rik van Riel wrote:
> On Fri, 30 Dec 2005, Marcelo Tosatti wrote:
> 
> > I think that final objective should be to abstract it away completly,
> > making it possible to select between different policies, allowing
> > further experimentation and implementations such as energy efficient
> > algorithms.
> 
> I'm not convinced.  That might just make vmscan.c harder to read ;)

Are you serious or just joking? :) 

Sure it might make it harder to read, but allowing selectable policies
is very interesting. Peter's patches go half-way into that direction.

Lets say, if CLOCK-Pro underperforms for a given workload (take into
account that its simply optimizing reclaim for a subset of all existing
access patterns, ie. heuristics), it would be easier for people to
develop/use different policies.

> > About CLOCK-Pro itself, I think that a small document with a short
> > introduction would be very useful...
> 
> http://linux-mm.org/AdvancedPageReplacement

I meant something more like Documentation/vm/clockpro.txt, for easier
reading of patch reviewers and community in general. 

> > > The HandCold rotation is driven by page reclaim needs. HandCold in turn
> > > drives HandHot, for every page HandCold promotes to hot HandHot needs to
> > > degrade one hot page to cold.
> > 
> > Why do you use only two clock hands and not three (HandHot, HandCold and 
> > HandTest) as in the original paper?
> 
> Because the non-resident pages cannot be in the clock.
> This is both because of space overhead, and because the
> non-resident list cannot be per zone.

I see - that is a fundamental change from the original CLOCK-Pro
algorithm, right? 

Do you have a clear idea about the consequences of not having           
non-resident pages in the clock? 

> I agree though, Peter's patch could use a lot more
> documentation.