Using large memory segments with a telnet session

Earnie Boyd
Thu Jan 4 07:53:00 GMT 2001

"Rist, Mark J." wrote:
> Thanks to the archive of this mailing list, I have discovered that you can
> use large memory segments with cygwin by modifying the registry key:
> HKEY_CURRENT_USER\Software\Cygnus Solutions\Cygwin
> and adding the value heap_chunk_in_mb (DWORD set to max memory amount).
> The problem that I am having is that I am logged into a machine via telnet
> using
> the inetutils. It appears that the registry setting is ignored for telnet
> sessions. So
> I can't run large memory programs when logged in remotely.
> The problem may be exaggerated by the fact that I am using roaming profiles
> and the registry for the user I am logging in as is stored remotely.
> I have tried several things to no avail:
> 1. Setting HKLM\Software\Cygnus Solutions\Cygwin\heap_chunk_in_mb
> I thought this might work since system wide mount points seem to be working
> and these are set under HKLM. Didn't work.
> 2. Setting HKCU\Software\Cygnus Solutions\Cygwin\heap_chunk_in_mb for the
> user running the inetd service. Nope.
> I am running out of ideas. I am fairly sure that I can recompile the
> cygwin1.dll and
> change the default heap size to get around this problem, but I would prefer
> to
> handle this as a configuration so that I don't have to recompile for every
> release.
> Any ideas?

Using the source I find:

 /* Note that reserving a huge amount of heap space does not result in
 swapping since we are not committing it. */
 /* FIXME: We should not be restricted to a fixed size heap no matter
 what the fixed size is. */

 heap_chunk_in_mb = reg.get_int ("heap_chunk_in_mb", 128);
 if (heap_chunk_in_mb < 4)
     heap_chunk_in_mb = 4;
     reg.set_int ("heap_chunk_in_mb", heap_chunk_in_mb);

So if your program isn't finding the registry key then the heap_chunk is
4mb not 128mb.  Also, you can see in the comments that there is no
reason for a fixed limit other than no one has patched the source yet. 
So, please, fix it and submit the patch to for
consideration.  You'll need to do the legal paper work with the release
forms at .


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