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Date: Thu, 30 Mar 2006 05:50:49 -0800 (PST)
From: Pete <null_geodesic AT yahoo DOT com>
Subject: Re: segfault on memory intensive programs
To: cygwin AT cygwin DOT com
In-Reply-To: <20060330121802.GG20907@calimero.vinschen.de>
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--- Corinna Vinschen <corinna-cygwin AT cygwin DOT com>
wrote:

> On Mar 30 12:14, Dave Korn wrote:
> > On 30 March 2006 12:08, Corinna Vinschen wrote:
> > 
> > 
> > >>> #define  N          600 // Matrix rank
> > >>> 	// We multiply m1 and m2, and put the result
> in m3.
> > >>> 	int m1[N][N];
> > >>> 	int m2[N][N];
> > >>> 	int m3[N][N];
> > 
> > > No wonder.  600**3 * sizeof (int) * 3 ==
> 2592000000 ~= 2.4 Gigs.
> > 
> >   Those matrices are only 2d!
> 
> Oh, hmm.  600**2 * sizeof (int) * 3 == 4320000 = 4.1
> Megs.
> 
> Maybe reserving a stack bigger than 4Megs would
> help, though?

Hi Corinna,

Thanks for looking at this!  :)

I've read the Cygwin FAQ for increasing stack and heap
size, but it doesn't seem to be working.  I allocated
more than enough memory, so I assume my linker
directives aren't having an effect.

Example output:

$ make
g++ -W -Wall -O9 -funroll-loops -mtune=pentium4   -c
-o matrix_mult_r.o matrix_mult_r.cc
g++ -W -Wall -O9 -funroll-loops -mtune=pentium4   -c
-o Timer.o Timer.cc
g++ -o matrix_mult_r.exe *.o
$ g++ -Wl,--heap,2048,--stack,8192 *.o -o
matrix_mult_r.exe
$ ./matrix_mult_r.exe
Segmentation fault (core dumped)

The Cygwin FAQ suggested a way of increasing the heap
size using a registry setting.  Is there a
corresponding way to use the registry to increase the
default stack size?

Also, I actually DID set registry setting
HKLM\SOFTWARE\Cygnus Solutions\Cygwin\heap_chunk_in_mb
to be 4096.  However, when I ran the test program
given in the Cygwin FAQ:

main()
{
  unsigned int bit=0x40000000, sum=0;
  char *x;
  
  while (bit > 4096) 
  {
    x = malloc(bit);
    if (x)
    sum += bit;
    bit >>= 1;
  }
  printf("%08x bytes (%.1fMb)\n", sum,
sum/1024.0/1024.0);
  return 0;
}

It reports back 1536 MB.   Very strange!  The registry
setting appears to not be having an effect.

Thanks again,
Pete

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