[nneonneo]

Why is it hard to calculate? Suppose I maintain lots of complex calculations that require variable amounts of buffered measurements (e.g. the last few seconds, the last few minutes at lower resolution, some extrapolations from measurements under different conditions, etc.). Freeing up the right measurements might be really tricky to get right, and if you free a critical measurement and need it later you’re hosed.

On the other hand, you can trivially calculate how many measurements you make per unit time, and multiply that by the size of the measurements to upper-bound your storage needs. Hypothetical example: you sample GPS coordinates 20 times per second, which works out to ~160 bytes/sec, 10000 bytes/min, or around 600KB for a full hour of flight. Easy to calculate - hard to fix.

[ken]

Are you taking into account memory fragmentation? Or the internal malloc data structures? If your record were just 1 byte more, it could easily double the total actual memory usage.

Memory usage is discrete, not continuous. It's not as simple as calculating the safety factor on a rope.

[cozzyd]

If you don't free, malloc doesn't need all that overhead