Re: why swap at all?

[Nick Piggin <nickpiggin@yahoo.com.au>]

John Bradford wrote:
> Hi,
> 
> Quote from Michael Brennan <mbrennan@ezrs.com>:
> 
>>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.