Re: Memory Fragmentation

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Steve Baker (steve++at++mred.bgm.link.com)
Fri, 23 May 97 08:51:44 -0500

> I have a suspected fragmentation problem with my shared memory arena.
>
> My flight sim application has an asynchronous DBASE process which pages
> database tiles as we traverse over the terrain. As it loads in each
> database tile, it creates a new branch with all the required pfNodes and
> attaches it to the scene graph with the pfMergeBuffer() call. When parts
> of the scene graph are no longer required, they are detached and
> pfAsyncDelete'ed.
>
> After flying around for a few hours, the application crashes trying to
> ammalloc some space, and a Performer message recommends that I increase
> the size of my arena.

...I'm pretty sure you are right - with a similar application, we see
a similar behaviour.

For a long time we suspected a memory leak - but after fighting for
weeks to try to find one, we eventually realised that it was indeed
memory fragmentation.

I don't think there is a fix for this - except to add more memory.

We found that with memory fragmentation, the graph of memory-used
versus time is like this:

|
| *****************
| ********
| *****
| ***
| **
| *
|*
|
|
|_____________________________________

But with a memory leak, it tends to be more like this:
    
| *
| *
| *
| *
| *
| *
| *
|*
|
|
|_____________________________________

So, you can eventually work out how much RAM it will
ultimately consume.

We found that for a given visual range, you might eventually
double the amount of memory you initially need - and it
doesn't finally asymptote out to a stable amount of memory
until you had been flying around for perhaps 3 to 8 hours.

Steve Baker 817-619-1361 (Vox-Lab)
Hughes Training Inc. 817-619-8776 (Vox-Office/Vox-Mail)
2200 Arlington Downs Road 817-619-4028 (Fax)
Arlington, Texas. TX 76005-6171 Steve++at++MrEd.bgm.link.com (eMail)
http://www.hti.com (external) http://MrEd.bgm.link.com/staff/steve (intranet)
                                http://web2.airmail.net/sjbaker1 (external)

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