perl's malloc/free keeps the memory for itself; gnu's malloc/free may return large chunks of freed memory to the linux kernel, and the kernel usually does not absorb it instantly the cleanup is on a cycle so you may have to wait way longer than 20 seconds for the release to take effect. Mac's compiler frees to the OS as well. so it really depends what system and malloc you use when compiling perl -- however his bprogram gaining that much memory usage points to perl not reusung the pool it has and growing vars not a freeing issue.

-Waswas