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Re: Documenting heap_chunk_in_mb

I saw that you were twisting in the wind with setting the registry setting.

I found out how, so I thought I would share.

In older releases, such as b19, the registery setting was

a DWORD setting called HKEY_CURRENT_USER/Software/Cygnus
Solutions/CYGWIN.DLL setup/b15.0/heap_chunk_in_mb, in the 1.3.3
release of cygwin, it is called HKEY_CURRENT_USER/Software/Cygnus

If you set a value of 4 in cygwin 1.3.3, quit out of all cygwin tools,
and then launch bash, it will give an error but otherwise start up,
indicating you are changing the right registry setting.  You can then
modify it to what value you want, pick a value no less than 160, but
no greater than around 1300.  I'm on NT 4.0.

Hopefully, someone will document this, if it isn't already.  I just
checked, and I don't see any documentation.

For completeness, why, why would someone need to use this?  Many
cygwin's have a limitation of how much heap they can use before malloc
will fail.  Older releases will complain with commit_and_inc:
VirtualAlloc failed type messages.  Newer releases won't say much, but
the application will usually complain about being out of memory.  Over
the years, people have just bumped up the base amount of memory that
cygwin will reserve for heap allocations (see, around
heap_chunk_in_mb) without fixing the `real' problem.  Current sources
just `fix' the heap at 256MB.  Slightly older cygwin's just allocated
128MB of heap.  If a user needs more, then they either have to have a
fixed cygwin1.dll, or set the registry setting.  A better long term
fix would be to alter the malloc/sbrk implementation for cygwin to be
able to use multiple chunks of address space and then allocate them on

The more stack space people reserve to their cygwin applications, the
less space that is available for heap.

Hope this information helps.

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