From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,7b69a8818c20ab9f
X-Google-Attributes: gid103376,public
From: Robert A Duff <bobduff@world.std.com>
Subject: Re: Y21C Bug
Date: 2000/01/06
Message-ID: <wcc66x7w220.fsf@world.std.com>#1/1
X-Deja-AN: 569160535
Sender: bobduff@world.std.com (Robert A Duff)
References: <84nqbo$q28$1@nnrp1.deja.com>
 <84o0g2$u8v$1@nnrp1.deja.com><84pvrs$7q1@ftp.kvaerner.com>
 <wccg0wfb02q.fsf@world.std.com> <84sltt$7s3@ftp.kvaerner.com>
 <84t966$be0$1@nnrp1.deja.com> <84vev2$7p4@ftp.kvaerner.com>
 <38737352.B282CC2@easystreet.com> <851j2q$78q1@ftp.kvaerner.com>
 <852dt0$vdl$1@nnrp1.deja.com>
Organization: The World Public Access UNIX, Brookline, MA
Newsgroups: comp.lang.ada
Date: 2000-01-06T00:00:00+00:00
List-Id: <comp.lang.ada>

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