Any way to reserve but not commit memory in linux?
You can turn this functionality on system-wide by using kernel overcommit. This is usually default setting on many distributions.
Here is the explanation http://www.mjmwired.net/kernel/Documentation/vm/overcommit-accounting
The Linux equivalent of VirtualAlloc() is mmap(), which provides the same behaviours. However as a commenter points out, reservation of contiguous memory is the behaviour of calls to malloc() as long as the memory is not initialized (such as by calloc(), or user code).