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Date: Wed, 30 Jun 2004 16:11:43 +0200
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Cygwin Memory Allocation and heap_chunk_in_mb
Message-ID: <20040630141143.GV19325@cygbert.vinschen.de>
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References: <Pine DOT CYG DOT 4 DOT 58 DOT 0406301444280 DOT 2112 AT ws3-mirp DOT geol DOT ucl DOT ac DOT uk>
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On Jun 30 14:54, Dan Hatton wrote:
> 
> I'm using CYGWIN_NT-5.1, under XP Pro.
> 
> I've set my heap_chunk_in_mb registry key to a very large value (10240
> decimal,) because I'm doing some RAM-hungry numerical calculations.
> 
> I have enough space to do this (Control Panel->System reports 12 GB of
> virtual memory allocated.)
> 
> However, the max_memory program at
> <http://www.cygwin.com/ml/cygwin/2003-02/msg00234.html> still reports
> only 1.5 GB available.  Sure enough, my program dies with an "out of
> memory" error at 1.25 GB (the 0.25 GB discrepancy is about right for
> the amount of RAM other processes are using.)
> 
> Anyone got any ideas what's happening, please?

The virtual memory available to a process is 2GB under NT.  I see two
possible workarounds:

- There's a way to start NT with a "/3gb" switch from boot.ini which
  allows to get 3GB of virtual memory per process.  Dunno if that's
  available on XP, perhaps the switch is only supported in server
  versions of NT.

- Use the AWE (Address Windowing Extension) functions available since W2K.
  You have to do memory mapping by yourself as necessary.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Co-Project Leader          mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

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