Linux memory/swap questions

[bob findlay]

I want use Linux in an embedded situation where I don't need/want swap.

In my application I plan to use (carefully) malloc/free as well as fork() 
calls.

In the back of my mind is the now legendary memory fragmentation problem 
which brought down a Mars mission a few years back.

I've noticed that it would appear that the Linux kernel is "lazy" when it 
comes to adding free'd memory back to the available pool.   ie. it will take 
new allocations from the unused pool first.     At some "low water" mark it 
seems to say "OK time to clean up".     Mind you I don't have any "hard" 
evidence to support this ... just observations via repeated uses of the free 
command.

My question is,   am I going to encounter problems with memory fragmentation 
to the level that perhap my fork() calls will begin to fail?  ie. I have 
enough memory, just not sufficient contiguous memory.

My understanding of swap is at best superficial, but is this not exactly the 
kind of situation which would cause the kernel to swap the oldest process out 
to make contiguous RAM available?

Is there a Linux system call which kicks it to do a memory cleanup?    Can 
memory cleanup even happen without swap around to use during the cleanup?

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