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From: Duncan Sands <baldrick@free.fr>
Newsgroups: comp.lang.ada
Subject: Re: Large arrays (again), problem case for GNAT
Date: Thu, 14 Apr 2005 09:45:20 +0200
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Date: 2005-04-14T09:45:20+02:00

> It is a well known and very old design flaw of many OSes including Linux,
> that successful allocation does not give you any amount of virtual memory
> until you commit the pages. It is not memory you are granted, it is even
> not virtual memory, it is address space which is worth of nothing. This
> controversy is as old as in-out parameters of Ada functions...

The reason for doing it is pragmatic: many programs allocate memory that
they never use.  By not actually giving them memory until they really use
it, there's more memory for other programs.  This makes writing programs
that fail gracefully in out-of-memory situations even harder than usual.
With Linux, you can choose the memory allocation policy on a system wide
basis, as I mentioned in another email.

Ciao,

D.