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Date: Fri, 18 Mar 2011 16:42:46 +0100
From: Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: ld: fatal error - cmalloc would have returned NULL
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On Mar 18 10:56, Christopher Faylor wrote:
> On Fri, Mar 18, 2011 at 03:40:48PM +0100, Corinna Vinschen wrote:
> >On Mar 18 11:23, Corinna Vinschen wrote:
> >> On Mar 18 02:08, Christopher Faylor wrote:
> >> > On Fri, Mar 18, 2011 at 05:47:04AM +0000, Dave Korn wrote:
> >> > >On 11/03/2011 13:53, Rainer Emrich wrote:
> >> > >
> >> > >> I have to be more clear. I increased the heap_chunk_in_mb to 1792 using:
> >> > >> regtool -i set /HKLM/Software/Cygwin/heap_chunk_in_mb 1792
> >> > >
> >> > >  I run with this setting all the time, I guess that's why I haven't seen this
> >> > >problem.  Before I did that (couple of years back) I also used to get crashes
> >> > >building libjava.
> >> > 
> >> > That setting should have nothing to do with cmalloc().  cmalloc is for
> >> > Cygwin's internal heap which has nothing to do with that setting.
> >> > 
> >> > Didn't Corinna already mention this?
> >> 
> >> In this case the bigger heap seems to avoid the aggressive use of small
> >> mmap chunks which in turn disallows to raise the cygheap size.  Without
> >> analyzing the whole situation there's not much else to say or do.  This
> >> is YA case which screams loudly for a testcase...
> >
> >I created an extensive testcase(*) and it turned out that the current
> >algorithm to allocate memory on the cygheap is wasting a lot of memory.
> >Actually it organizes the memory in buckets, each of which cares for a
> >specific size as a power of 2.  So memory on the cygheap is always
> >allocated in chunks of 4 byte, 8 byte, 16 byte, 32 byte, etc.  Plus,
> >every chunk needs extra 8 byte for bookkeeping.
> 
> Right.  That's a fairly classic implementation of malloc which was, in
> this case, implemented by DJ Delorie.  I chose that from a few other
> implementations because it was, at the time, supposed to be the best
> tradeoff between speed and memory usage.  But, back when I implemented
> the cygheap it wasn't used as much as it is now, which I guess is
> fairly obvious.

Maybe we should modify the implementation at one point, but for now I'm
wonderin if we shouldn't just raise the cygheap size to 2 Megs.  It's
still not much memory given today's RAM sizes, and it's only a fraction
of the application's address space.  But it is enough so that ld's
address space will be exhausted before the cygheap is exhausted.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Project Co-Leader          cygwin AT cygwin DOT com
Red Hat

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