Re: [ck] Re: [PATCH][RFC] vm: swap prefetch

[Pedro Venda]

On Thursday 01 September 2005 14:18, Con Kolivas wrote:
> On Fri, 2 Sep 2005 00:18, Hans Kristian Rosbach wrote:
> > On Thu, 2005-09-01 at 23:46 +1000, Con Kolivas wrote:
> > > Here is a working swap prefetching patch for 2.6.13. I have
> > > resuscitated and rewritten some early prefetch code Thomas Schlichter
> > > did in late 2.5 to create a configurable kernel thread that reads in
> > > swap from ram in reverse order it was written out. It does this once
> > > kswapd has been idle for a minute (implying no current vm stress). This
> > > patch attached below is a rollup of two patches the current versions of
> > > which are here:

> > That said, I have often thought it might be good to have something like
> > pre-writing swap, ie reverse what your patch does.
> >
> > In other words it'd keep as much of swappable data on disk as possible,
> > but without removing it from memory. So when it comes time to free up
> > some memory, the data is already on disk so no performance penalty from
> > writing it out.

both ideas make all the sense to me. I'll give it a try, but in what way can 
we test this kind of enhancement? maybe write a small program that starts 
fills a good part of swap space and then, after 1min idle, 'watch free -m' 
should show free memory decreasing (not counting cache/buffers) with idle 
activity. decent?

about the Hans's proposal - it would increase power consumption, because of 
increased disk activity. about con's swap prefetch, I'm not so sure...

regards,
pedro venda.
-- 

Pedro João Lopes Venda
email: pjvenda < at > arrakis.dhis.org
http://arrakis.dhis.org

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