[rhelv6-beta-list] My first experiences with RHEL6 beta

[John Summerfield]

James Findley wrote:

> In my experience, IO is such a precious and limited resource (increasing 
> IO throughput, as opposed to amount of storage available, is often 
> extremely expensive) that using it for swap is very counter productive. 
>  I typically give VMs about 250M of swap, and set vm.swappiness to a 
> very low value (sometimes even 0) in my VMs.
> But I'm sure this is highly application/environment dependant, so if 
> using lots of swap works for you, great.
> Wanted to present a counterexample though as it isn't always the best 
> thing to do.


In any system, with any OS, paging and swapping are wasted resources. 
Time spent swapping and paging is time not available for doing the work 
at hand.

Paging and swapping were invented to overcome other problems such as 
lack of real memory (very expensive it used to be) and poor/limited 
performance from the then-current solution, overlays.

Creating well-performing overlay setups used to be quite a skill, when I 
was a young programmer.

I well remember when IBM introduced virtual storage, and we had IBM 
people around to educate us about the implications for writing programs. 
For example, the order in when elements of an array can be important - 
if each reference hits a different page, that's another page that can't 
be written out to disk (if dirty) and discarded.

It's a long time since I saw any mention of such considerations, these 
days people ignore the differences between real and virtual storage.




-- 

Cheers
John

-- spambait
1aaaaaaa at coco.merseine.nu  Z1aaaaaaa at coco.merseine.nu
-- Advice
http://webfoot.com/advice/email.top.php
http://www.catb.org/~esr/faqs/smart-questions.html
http://support.microsoft.com/kb/555375

You cannot reply off-list:-)