Re: excessive swapping

[Florin Andrei]

On Thu, 2004-08-12 at 23:44, Florin Andrei wrote:
> On Thu, 2004-08-12 at 23:40, Florin Andrei wrote:
> 
> > The system is swapping excessively. There's no way the total size of the
> > applications exceeds the size of RAM. There's plenty of room to spare,
> > yet 16% of the 530MB of swap is used.
> 
> Now it's 22% and counting. Way to go. :-(

Now it's 27%. You get the picture.

Anyway, out of the 512MB of RAM, like 390MB are disk cache. No wonder
that the useful pages are swaped out.

It seems like the kernel believes that the disk cache has some
miraculous properties w.r.t. the system performance, and desperately
tries to grow it as much as possible.
This is wrong religion. The reality is opposite. The system is much
slower, because applications are thrown out in the swap, then sucked
back in, which is a very slow process.

The efficiency of increasing the disk cache decreases exponentially with
size, like any other cache. Then what's the point of sacrificing useful
memory just to increase some hypothetical "useful" cache?

Even on a server, the same universal laws still apply, the efficiency of
increasing cache still decreases exponentially. There's still precious
time wasted when an application is sucked back in from swap, at the
price of an immeasurably small performance gain due to the disk cache
being larger.

I'm sorry for rambling, but to me the current swapping policy is so
blatantly wrong. Besides the space occupied by the apps themselves,
there's a lot of room to _spare_ - then why swap?

-- 
Florin Andrei

http://florin.myip.org/

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