Subject: Re: Bad response...
To: None <>
From: Richard Earnshaw <>
List: current-users
Date: 08/31/2004 11:18:47
On Mon, 2004-08-30 at 15:10, Thor Lancelot Simon wrote:
> I'm claiming that your expectations are way out of line.  You're trying to
> work with data and executables that are somewhere between one and two orders
> of magnitude as large as they were when the amount of memory on your system
> was appropriate for its job -- yet expecting performance to be good with
> default system tuning.  I think that's absurd, and I think that changing the
> default system tuning to accomodate this use would probably break more than
> it fixes.
> As I pointed out, the working set of your system vastly exceeds the size of
> its physical memory.  You're not going to see good performance in that case,
> no matter what you do; all you can really do is choose which applications on
> the system will get hit the worst with lousy performance.

I think the real problem here is that the default algorithms used to
determine the amount of memory to allocate for each specific purpose are
based on a simple (linear) percentage of the total memory.  On large
machines the algorithm works acceptably well.  As you scale the amount
of physical ram back then it turns out that they are too aggressive: the
on small machines the kernel must not only cache less it must cache
significantly less -- the scaling is not linear.

> Really, in an era in which common desktop applications approach 50MB in
> size (I just double checked my running copy of Netscape -- it's 40MB!) and
> the data those applications work with is also far larger than one might
> naively expect, your best solution is probably just to reach in your wallet
> and buy some more RAM -- which also happens to cost about two orders of
> magnitude less than it used to.

No, you can't always do that.  Machines have a physical limit to the
amount of RAM that they can manage -- many of the machines I have are
fully populated in RAM, but they still don't have enough.  And how do
you expand the RAM in your PDA?

Nobody is expecting that a machine with 64M of memory is going to
perform as well as one with 1G+, but they don't want their applications
to be thrashing about in 10M because the system has 'stolen' the rest
for caches that are used less often than the pages in the application. 
That's the situation we have now.