Re: [lc-devel] Re: [Openmosix-devel] oM + cc doesn't mixw

[Rodrigo S. de C. <rc...@im...>]

Hi Jordi,

Long time no see!

On Sat, May 24, 2003 at 12:43:27PM +0200, Jordi wrote:
> > Compressed swap is tied to compressed cache implementation, so
> > porting it (without compressed caching) would require some
> > work. BTW, when I implemented compressed swap, my focus was mostly
> > swapping on disk, where the transfer rate isn't a critical
> > matter. I was actually interested in reducing the number of IO
> > operations, hence checking this compression impact on the
> > performance. Given the initial design and implementation, I think
> > there is much room for improvement in this code, if we came to the
> > conclusion it may be worth adding this feature to openMosix.
> >
> 
> It's a long time since i last read code of Openmosix or cc but at
> that time at least it was not difficult to mix both
> projects. Dealing with compressed pages is not more difficult that
> dealingg with swap space.

Great to hear your opinion. I never read OpenMosix code, but my guess
would be the same as yours: supporting compressed pages in OpenMosix
would require much more work than compressed swap.

> The main problem i see is a philosofical problem.  Openmosix when
> tryingg to optimice CPU (load balancing processes accordiing to CPU
> usage) assumes that CPU must be optimize but net bandwidth and
> computer I/O is cheap and fast. So it's worthy to sacrify I/O to
> CPU.  mm-cc is assuming that CPUs doubles their power every 2 years
> but the rest of the computer components advance more slowly. So it's
> worthy to sacrify CPU to I/O.

Yes, we sacrifice CPU to reduce I/O operations. In general, it is
worthwhile for general system performance. 

I don't know much about OpenMosix project, but it still may be worth
to compress a number of pages to reduce the I/O (disk and network) if
the general performance gets some improvement out of it (even if
spending some CPU cycles compressing it). What do you think?

> I don't know (as i'd make no test) what can happend missing both
> projects.  Missing both projects correctly seems a different project
> to me. Where yoou can specify if you want to optimize CPU and disk
> access but no networking or the other way round so it manage both
> openmosix and mm-cc to use more one resource or other one.

Mixing these projects would introduce another variable to compressed
cache code to know when it has to compress some pages. But I don't
know if I would make any distinction between disk and network, since
when you have compressed memory pages, disk may benefit from the
compression, as well as networking (e.g. data migration). I hope it
makes sense.

Regards,
-- 
Rodrigo