Re: why swap at all?

[Nick Piggin]

John Bradford wrote:
> Hi,
>
> Quote from Michael Brennan <mbrennan@xxxxxxxx>:
>
> > Hi!
> > I've recently started to follow this list.
> > I read the swap discussion here, and I was wondering about what Nick 
> > Pigging said about grepping the kernel tree.
> >
> > Nick Piggin wrote:
> > > For example, I have 57MB swapped right now. It allows me to instantly
> > > grep the kernel tree. If I turned swap off, each grep would probably
> > > take 30 seconds.
> >
> > Are the pages swapped to disk as a result of the grep run?

The pages are gradually swapped to disk as I use the system.
> I'm not really sure what the above was intended to demonstrate, but I assume
> that it was that having swap allowed the first grep to fill physical RAM with
> cache at the expense of swapping other processes, which were using physical
> RAM to disk.

Well, at the "expense" of paging out unused memory. I don't see
any swapin.

> However, if 57 Mb of swap allows this, 57 Mb of extra physical RAM should also
> also allow the grep to be cached, without having to swap out anything.

Well yes, but if I had another 57MB of physical memory then I would
still turn on swap so that other 57MB of unused memory isn't wasted.
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