Reading huge files using Memory Mapped Files

Question

I see many articles suggesting not to map huge files as mmap files so the virtual address space won\'t be taken solely by the mmap.

How does that change with 64 bit

Answer 1

There's a reason to think carefully of using memory-mapped files, even on 64-bit platform (where virtual address space size is not an issue). It's related to the (potential) error handling.

When reading the file "conventionally" - any I/O error is reported by the appropriate function return value. The rest of error handling is up to you.

OTOH if the error arises during the implicit I/O (resulting from the page fault and attempt to load the needed file portion into the appropriate memory page) - the error handling mechanism depends on the OS.

In Windows the error handling is performed via SEH - so-called "structured exception handling". The exception propagates to the user mode (application's code) where you have a chance to handle it properly. The proper handling requires you to compile with the appropriate exception handling settings in the compiler (to guarantee the invocation of the destructors, if applicable).

I don't know how the error handling is performed in unix/linux though.

P.S. I don't say don't use memory-mapped files. I say do this carefully