ANN: VMTester - virtual memory testing utility
ANN: VMTester - virtual memory testing utility
- Subject: ANN: VMTester - virtual memory testing utility
- From: Cameron Hayne <email@hidden>
- Date: Tue, 05 Apr 2005 17:44:08 -0400
I wrote a little utility app that you might find interesting. I call it
"VMTester" as it provides a test platform for trying to understand the
behaviour of OS X's virtual memory system as applications allocate and
de-allocate memory. You can get the executable (and if you want them, the
source code files) from:
http://hayne.net/MacDev/VMTester/
It illustrates various aspects of Cocoa programming and so the source code
might be useful as an educational resource even if you aren't interesting in
its specific functionality. This application was partially inspired by Shawn
Erickson's "Memory Muncher" app.
I wrote it partly for use in explaining to all the people on the macosxhints
forum who ask about why their "free" memory is always so low. I thought it
would help if they could try experiments and see the effect on the various
RAM categories (wired, active, inactive, free).
But so far, I find that it is proving some of my previous statements wrong -
those about the "inactive" memory. Of course, it's not entirely my fault
since I was just repeating what Apple has said in its developer docs
(http://developer.apple.com/documentation/Performance/Conceptual/ManagingMem
ory/Concepts/AboutMemory.html) and in this relatively recent article on
Activity Monitor: http://docs.info.apple.com/article.html?artnum=107918
When I allocate memory using my VMTester app, I see that it is adding to the
"inactive" list. I had expected to see it added to the "active" list instead
- so clearly I really don't understand what is going on. And this seems to
mean that my previous statements (e.g. on macosxhints forums) about the
available RAM being effectively the sum of "inactive" and "free" were wrong.
Note that VMTester does try to make the allocated memory be active by
writing and reading from it periodically.
Free free to hand this app on to whoever might be interested - it is
licensed under the GPL. I would be especially interested in hearing from
some of Apple's VM-engineers if they have any explanation of what this app
is showing with the "inactive" memory.
--
Cameron Hayne (email@hidden)
Hayne of Tintagel
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