From: lhall AT rfk DOT com (Larry Hall)
Subject: Re:
8 Apr 1998 07:59:31 -0700
Message-ID: <3.0.5.32.19980408103122.00a07e80.cygnus.cygwin32.developers@pop.ma.ultranet.com>
References: <199804081301 DOT JAA24373 AT tweedledumb DOT cygnus DOT com>
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To: cgf AT cygnus DOT com, cygwin32-developers AT cygnus DOT com

At 09:01 AM 4/8/98 -0400, cgf AT cygnus DOT com wrote:
>>From: ian AT cygnus DOT com (Ian Lance Taylor)
>>Date: 7 Apr 1998 21:03:43 -0700
>>
>>>From: Geoffrey Noer <noer AT cygnus DOT com>
>>>Date: Tue, 7 Apr 1998 18:41:15 -0700 (PDT)
>>
>>>Sergey Okhapkin wrote:
>>>> 
>>>> Now I know why _every_ cygwin process have a splitted heap if it allocates 
>>>> more than heap_chunk_size bytes of memory (but I will not tell you why this 
>>>> happens - think yourself!-) Here is the temporary fix - reserve a large 
>>>> amount of memory for heap to avoid fork problem. The fix doesn't affect 
>>>> performance.
>>>> 
>>>> H:\usr\src\cygnus\cdk\winsup>diff -u shared.cc.orig shared.cc
>>>> --- shared.cc.orig      Wed Feb 11 06:15:08 1998
>>>> +++ shared.cc   Tue Mar 24 10:44:55 1998
>>>> @@ -96,7 +96,7 @@
>>>> 
>>>>    reg_session reg;
>>>> 
>>>> -  heap_chunk_in_mb = reg.get_key ().get_int ("heap_chunk_in_mb", 8);
>>>> +  heap_chunk_in_mb = reg.get_key ().get_int ("heap_chunk_in_mb", 128);
>>>>    if (heap_chunk_in_mb < 4)
>>>>      {
>>>>        heap_chunk_in_mb = 4;
>>>
>>>Are there reasons why I shouldn't make this change?
>>
>>On a traditional Unix system, making this change would mean that every
>>process would require 128 MB in the swap file, and your system would
>>rapidly run out of swap space.  I don't know how the Windows
>>equivalent of a swap file works, so I don't know whether there would
>>be any equivalent problem.
>
>Since the this just essentially sets aside a contiguous address range I
>could envision an OS which would be intelligent enough to avoid allocating
>swap space until parts of the memory region were committed.  I'm having
>a difficult time, however, imagining a *Windows* operating system that
>would be this intelligent.

I believe the NT VMM allows you to do this.  But you're right, I'd be
surprised to find out that Win95 can handle this properly.  Then again,
I haven't checked it myself yet!:-)


Larry Hall                              lhall AT rfk DOT com
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