Your system: memory is released, kernel clears it in the background, wasting write bandwidth (which might not matter for anything except power if the system was idle at the time), and when the user-mode program starts using it, it will start writing and every new line they write to will trigger a spurious read.

Modern Linux: memory is released, kernel lets it lie, not using any power or bandwidth to do anything to it, until an user-mode program allocates it and touches the page. Then the kernel picks up the page, writes the entire page with 0:es using whatever idiom on that CPU allows it to just allocate the page in cache without reading it from the RAM. This is really fast, faster than a single memory fetch. The user-mode program can then directly use it without having to fetch anything from DRAM.

Nit: it's faster than a page fault (so fault + zeroing is pretty much the same as just fault).

According to the recent-ish Latency Numbers, a main memory reference is ~100ns (variable by arch and local v remote DRAM) which is about the same as zeroing a page, at least with respect to the dragonfly numbers I posted above.