Re: Y21C Bug

[Robert A Duff <bobduff@world.std.com>]

Robert Dewar <robert_dewar@my-deja.com> writes:

> 1. The ability to declare very large areas of memory with
> commit-on-use semantics. There are many uses of this. I have
> the feeling that a lot of programmers still don't understand
> commit-on-use.

Commit on use is indeed very cool.

Do you know which operating systems support it?

> 2. The ability to map file systems into virtual memory.

When I first used a virtual memory system (32-bit address space), I
thought mapping files memory into was obviously the "right" way to do
all disk I/O.  At the time, the notion that a file might be too big to
fit seemed ludicrous.  Nowadays some people really do want to create
files bigger than 4G.

But it really *can* work in a 64-bit address space.

On the other hand, if I'm writing a program that creates a lot of
records in the heap pointing at one another, then a large portion of the
data is actually addresses, and I'm not sure I want to double the size
of *all* my addresses (thus almost doubling the size of all my data).
The folks who say "memory is cheap" are wrong: using more memory usually
costs more time (eg increases cache misses), and *time* is not cheap.

- Bob