My knowledge is years out of date, but does WASM still require the application to request its maximum memory footprint up-front? Granted, that's what Sun/Oracle's JVM has been doing to allocate its heap from the OS for well over a decade, but I'm also not aware if WASM is able to use the equivalent of madvise() to tell the browser/OS that it's fine to unmap a region of memory and map it back zeroed-out when it's next needed.
Yep you need to specify the maximum memory amount up-front. Its defined as "webassembly memory pages". Each page is 64kb. You need to specify an initial and a maximum amount. The webassembly module can call memory.grow() to grow it by a page until it reaches the maximum. Though you can't "un-grow" or decrease the amount of allocated memory.
