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From: "Dave Korn" <dk AT artimi DOT com>
To: <cygwin AT cygwin DOT com>
Subject: RE: Cygwin Memory Allocation and heap_chunk_in_mb
Date: Wed, 30 Jun 2004 15:06:52 +0100
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X-OriginalArrivalTime: 30 Jun 2004 14:06:52.0640 (UTC) FILETIME=[7E684E00:01C45EAB]

> -----Original Message-----
> From: cygwin-owner On Behalf Of Dan Hatton
> Sent: 30 June 2004 14:55

> 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?


Errm... just checking the obvious, but.... you _are_ using a 64-bit system,
right?

Because no amount of virtual memory can get around the fact that there's
only 4Gb of addresses in the per-process memory space, and 2Gb of those
belong to the kernel.

Of course, even if you are on a 64bit system, cygwin itself isn't 64-bit.
malloc (as used by that test program) returns a 32-bit pointer.  There's no
way of allocating more than 4Gb without malloc having to start returning
duplicate values!

Try adding a line to your boot.ini to allow you to boot with the /3Gb
switch, and see if that gets you an extra gig of memory.  See
http://support.microsoft.com/default.aspx?scid=kb;EN-US;833721 
for details.

    cheers, 
      DaveK
-- 
Can't think of a witty .sigline today....


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