using mmap on large (> 2 Gig) files

[sturlamolden]

Martin v. Löwis wrote:

> You know this isn't true in general. It is true for a 32-bit address
> space only.

Yes, but there are two other aspects:

1. Many of us use 32-bit architectures. The one who wrote the module
should have considered why UNIX' mmap and Windows' MapViewOfFile takes
an offset parameter. As it is now, "mmap.mmap" can be considered
inadequate on 32 bit architectures.

2. The OS may be stupid. Mapping a large file may be a major slowdown
simply because the memory mapping is implemented suboptimally inside
the OS. For example it may try to load and synchronise huge portions of
the file that you don't need. This will deplete the amout of free RAM,
and perhaps result in excessive swapping. "mmap.mmap" is therefore a
potential "tarpit" on any architecture. Thus, memory mapping more than
you need is not intelligent, even if you do have a 64 bit processor.
The missing offset argument is essential for getting adequate
performance from a memory-mapped file object.