Strange memory problems

[Eugene]

>> With Apache stopped, it goes down to RSS=0.5GB and VSZ=0.6G -- but 
>> Inactive
>> Memory remains above 2.5GB.
>> Is it a memory leak somewhere or what?
>
> That looks quite normal to me, apart from the zombie process. FreeBSD 
> always
> attempts to occupy most of the RAM, because it's a very fast way of saving
> information, and after all a lot of RAM is of no use if there's nothing in
> it. So long as no other program needs it for more "important" information,
> there's nothing wrong with keeping a lot of "unimportant" stuff around in
> case it is needed again quickly.

Ok, that's nice. However, I was concerned not so much with low Free memory 
as with Act+Inact being 1.5-4 times greater than size of running processes. 
What data is there, exactly? I don't think it has more than 1GB of unsynced 
disk writes?

Also, a more general question: how do I estimate 'real' memory load? 
Sum(RSS) + 0.5*DiskCache  ?
For example, I would like to know (in advance) e.g. how many Apache 
processes we can handle before memory becomes a problem.
Do you think it would be nice if top(1) could give some consolidated 
measure -- probably taking into account usage statistics and/or response 
time?
Or at least two measures -- e.g. "How much memory can be allocated off-hand 
without any disk I/O" and "How much memory can be allocated so that swapped 
data would not have to be re-read again in reasonable time"?

Thanks a lot
Eugene