Subject: VMM040 & Imagine phases
Date: Tue, 3 May 94 07:26:07 -0600
From: Steve Koren <koren@hpfcogv.fc.hp.com>

Lots of people ask: "where can I get VMM040"?  Its on aminet...  Version
1.2 is the latest.

Someone wrote:

> I have vmm40 working with imagine also, and it renders fine but when
> it goes into the cleanup phase after rendering a frame it does an
> inordinate amount of paging. The cleanup phase sometimes takes over 10

During cleanup phase, Imagine is probably free()ing all the memory that
it has malloc()ed.  Thus, it would need to touch every single allocated
VM page it allocated, and probably not in order, which is a bummer for
the VM system.

Rendering, however, should work very well as long as you don't try to
have too large a ratio of VM to physical RAM (see below).  I've rendered
things with a ratio of about 3 (24 Mb VM backed by 8 Mb physical RAM on
an 18 Mb system) and I think my render phase was not more than 1 or 2%
slower than it would have been otherwise.  The percentage increases for
short renders, however.  For a 1 minute render, I might spend 20% of the
time swapping.  For a 1 hour render, you swap about the same _absolute_
amount but you do it over a much larger time span, so the percentage is
less - ie, still 12 seconds of swaping, but 12 sec spread over an hour
isn't much.  I find that in the above situation my machine tends to swap
when rendering for about one page every 10 seconds, which isn't even
noticeable.  Very small price to pay for effectively having a 40 Mb
system :-)

>   - 18 meg ram
>   - 20meg vmm40 partition
>   - 2 meg vmm40 buffer

By "2 Mb vmm40 buffer", do you mean that you are trying to back 20 Mb of
virtual memory with 2 Mb of physical memory?  If so, that'll be hard for
any VM system to cope with without a lot of paging.  The general rule of
thumb is that the amount of physical ram you use to back your VM should
be at least as big as your maximum working set size.  If you have 18 Mb
physical RAM, I'd suggest allocating about 8 to 10 Mb of that for VMM's
use.  That'll still give you quite a few Mb for things which don't use
virtual memory.  One other good thing to allocate to VM is CLI window
scrollback buffers.  I tend to use 128 K scrollback buffers, and have 5
to 8 CLI windows open at once, so that could be a megabyte of scrollback
buffer that I might as well have paged out most of the time so Imagine
has more memory for rendering!

  - steve


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