How can I reserve virtual memory in Linux?
linux, mmap, windows
Solution
I believe you should be able to achieve the same by mapping anonymous memory with `PROT_NONE`. Accessing `PROT_NONE` memory will result in a segfault, but the memory region will be reserved and not used for any other purpose. If you want to allocate a very big chunk of memory, add `MAP_NORESERVE` to ensure that the default overcommit mechanism won't check your allocation.
`PROT_NONE` is commonly employed for "guard" pages at the end of stacks.
Problem
I have an application that reserves a contiguous memory block using VirtualAllocEx on Windows with the MEM_RESERVE flag. This reserves a virtual memory block, but does not back it with a physical page or page file chunk. Hence, accessing the allocated memory will result in a segmentation fault -- but other allocations will not intersect with this virtual memory block. How can I do the same for Linux with mmap? I did notice the answer in this question, but does that really guarantee that say, 1 GB of physical memory won't be allocated to my process if I don't touch the allocated pages? I don't want any thrashing problems.