alt Hacker NewsIt still works if the file doesn't fit in RAM
No it doesn't. If you have a file that's 2^36 bytes and your address space is only 2^32, it won't work.
On a related digression, I've seen so many cases of programs that could've handled infinitely long input in constant space instead implemented as some form of "read the whole input into memory", which unnecessarily puts a limit on the input length.
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You can mmap with offset, for that case. Just FYI in anyone thought it was a hard limit.
All memory map APIs support moveable “windows” or views into files that are much larger than either physical memory or the virtual address space.
I’ve seen otherwise competent developers use compile time flags to bypass memmap on 32-bit systems even though this always worked! I dealt with database engines in the 1990s that used memmap for files tens of gigabytes in size.
Address space size and RAM are two different things.