They can all change file size according to my test. why can they all change file to larger and to shorter? what's the difference between fallocate and ftruncate?

I need to allocate huge file without zeroing it's content. I'm producing this steps fopen => ftruncate => fclose => mmap => (...work...) => munmap with huge file sizes (hundreds of g...

I would like to be able to zero out a range of a file memory-mapping without invoking any io (in order to efficiently sequentially overwrite huge files without incurring any disk read io). Doing s...