This is only really a problem if you accept overcommit as a force of nature that can't be changed or tweaked (you can still do address space reservation without needing overcommit)

If you don't, it becomes rather easy (and strict commit accounting is done for example on Linux even if it isn't used in some cases)

Memory mapped files can be entirely recreated from the disk so no need to charge for them. Anonymous pages (whether private or shareable) have to be charged. Shareable memory is the harder one to charge. (The case where a mapping is used by only one can get charged as private commit.) These two previous cases are charged even if in a swap file or whatnot