Date: Fri, 18 Mar 2011 10:56:13 -0400
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: ld: fatal error - cmalloc would have returned NULL
Message-ID: <20110318145613.GA10232@ednor.casa.cgf.cx>
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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.

cgf

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