memory spikes during heap allocation

[Erickson, John]

Hello,

I have a program that gradually allocates more data on the heap.  I have noticed that periodically erlang seems to allocate more space for my process.  One strange thing, though, is that it appears when this happens there is a spike in memory usage that is only temporary.  Sometimes these spikes can be quite large.  I was wondering if there is any explanation for this.  For example, does GC or heap allocation require a large amount of temporary work space?

I guess one good thing is that it appears it is mostly a spike in virtual memory; actual memory usage doesn't seem to spike nearly as much.  I wonder if actual pages are being written to disk or if somehow they are just temporarily allocated and released without being written.

32346 jerickso  25   0 3394m 2.7g 2224 S 99.8 17.5  12:30.84 beam.smp
32346 jerickso  25   0 3412m 2.8g 2224 S 49.6 17.9  12:32.33 beam.smp
32346 jerickso  25   0 5040m 3.4g 2224 S 86.9 21.5  12:34.94 beam.smp            <<<<<<---------- Here's a spike!!
32346 jerickso  25   0 3724m 2.7g 2224 S 72.9 17.5  12:37.13 beam.smp
32346 jerickso  25   0 3723m 2.8g 2224 S 34.3 17.7  12:38.16 beam.smp

John