Message-ID: <108fc8470605102346g162674fdic41c75613e4dc3e4@mail.gmail.com>
Date: Thu, 11 May 2006 02:46:28 -0400
From: "Brad Krane" <brad DOT krane AT gmail DOT com>
To: "Cygwin General List" <cygwin AT cygwin DOT com>
Subject: Increasing Available Memory for Cygwin Run Programs in XP
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I am trying to run a numerical simulation that requires a large amount
of RAM in the cygwin environment running on a Pentium 4 with Windows
XP and 3GB RAM. I have so far learned that Windows XP (and other
Windows versions) allot only 2GB RAM for user program space. I have
verified this with a small program I developed that allocates the
maximum available memory to 4 bytes.
In Windows when I run this program I am able to allocate a total of
1.94GB of memory, however, when I run the same code in Cygwin I am
only able to allocate 1.12GB of memory.
I am not the only person to have come across a similar problem in the
past. I have been searching through the archives and so far have found
3 notable references from topics that can be found here:

http://sourceware.org/ml/cygwin/2005-04/msg01309.html
http://sources.redhat.com/ml/cygwin/2003-02/msg00234.html
http://sourceware.org/ml/cygwin/2004-06/msg01248.html

In the first topic it is said that using the -mno-cygwin flag in the
compiler options will allow programs to gain access to more memory by
having them by pass the cygwin1.dll. This however produces the
undesirable side effect of an error compiling, as the program
references sys/resource.h and I can only assume that this would
require the use of cygwin1.dll. I don't suppose there is much of a way
around this?

The second idea I found was to set the registry item
"/HKEY_CURRENT_USER/Software/Cygnus\ Solutions/Cygwin/heap_chunk_in_mb
x" where 'x' is the amount in MB(obviously). I set this value to a
safe amount of 1950000MB or 1.90GB. Unfortunately this does nothing
and I am left with the exact same amount of memory.

Finally there was the idea to run XP with the /3gb option set in the
boot.ini to increase the user program space from 2GB to 3GB. The
problem is that after a reboot I am still only able to allocate 1.94GB
of RAM with a Windows XP binary and 1.12GB through Cygwin. Could this
be a side-effect of having only 3GM or physical memory or would the
page file accommodate this(as I think)?

I've noticed that the messages are at least one year old. Has anything
significant that would affect these "fixes" have changed since then?
Does anyone have any fresh ideas or work around aside from a new OS?
;)

On a further note I have noticed that in the Advanced Properties of
the Cygwin shortcut that is set to run in a separate memory space by
default and I am unable to change this even when making a shortcut
directly to bash.exe itself. Could this be affecting the available
memory and if so is there anyway to modify this property?

Thank you for your time and effort.

-- 
Brad

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