如何在保留虚拟地址范围的同时释放内存？

Question

I'm working on a device that has very tight memory size and virtual address space constraint.

I'm trying to solve this problem by reclaiming memory more frequently while reclaiming virtual address less frequently, eg reserving virtual address early but committing memory late, while reclaiming memory early and releasing virtual address late.

Particularly there is a very large allocation that suffers a lot from address space fragmentation and I'm trying to solve it by reserving address space for it up front.

This question solves the first problem: use mmap with PROT_NONE to acquire virtual address range, and use mprotect with PROT_READ|PROT_WRITE before use, and then pages would be faulted in when used.

However, I couldn't find a way to do the reverse: mprotect with PROT_NONE doesn't seem to release the pages, while calling munmap loses the virtual address range.

Is there to unmap/detach pages while preserving virtual address?

Answer 1

带有MAP_FIXED mmap将替换指定地址范围内的任何现有映射，并在不再引用该内存时释放其内存。