Re: An idea for prefetching swapped memory...

[Jörn Engel]

On Mon, 7 April 2003 10:19:25 -0400, Chris Friesen wrote:
> 
> With the current setup though, the memory is wasted.  It makes sense that 
> we should fill the memory up with *something* that is likely to be useful.
> 
> If I have mozilla open, start a kernel compile, and then come back half an 
> hour later, I would like to see the mozilla pages speculatively loaded back 
> into memory.
> 
> Since the system is otherwise idle, it doesn't cost anything to do this.

In the scenario above, it costs you a lot. The memory is completely
used, else mozilla wouldn't get swapped out. If you swap it back in
and get rid of fs cache, the next kernel (compile|grep|whatever) will
be slower.

And even in the original scenario, it will be expensive, depending on
your machine. On a notebook, it costs you battery power, which is a
limited resource, *for sure*. You *may* save user time, which *may* be
a limited resource, but not always.

But sure, it is a fun project to hack on, just go ahead and show the
numbers. :)

> I think its obvious that it is beneficial to swap in something, the only 
> trick is getting a decent heuristic as to what it should be.

And when it should be done. ;)

Jörn

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