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1049

answers:

3

Hi,

I'm getting this error while doing a git svn rebase in cygwin

Out of memory during "large" request for 268439552 bytes, total sbrk() is 140652544 bytes at /usr/lib/perl5/site_perl/Git.pm line 898, <GEN1> line 3.

268439552 is 256MB. Cygwin's maxium memory size is set to 1024MB so I'm guessing that it has a different maximum memory size for perl?

How can I increase the maximum memory size that perl programs can use?

update: This is where the error occurs (in Git.pm):

 while (1) {
      my $bytesLeft = $size - $bytesRead;
      last unless $bytesLeft;

      my $bytesToRead = $bytesLeft < 1024 ? $bytesLeft : 1024;
      my $read = read($in, $blob, $bytesToRead, $bytesRead); //line 898
      unless (defined($read)) {
         $self->_close_cat_blob();
         throw Error::Simple("in pipe went bad");
      }

      $bytesRead += $read;
   }

I've added a print before line 898 to print out $bytesToRead and $bytesRead and the result was 1024 for $bytesToRead, and 134220800 for $bytesRead, so it's reading 1024 bytes at a time and it has already read 128MB. Perl's 'read' function must be out of memory and is trying to request for double it's memory size...is there a way to specify how much memory to request? or is that implementation dependent?

UPDATE2: While testing memory allocation in cygwin: This C program's output was 1536MB

int 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;
}

While this perl program crashed if the file size is greater than 384MB (but succeeded if the file size was less).

open(F, "<400") or die("can't read\n");
$size = -s "400";

$read = read(F, $s, $size);

The error is similar

Out of memory during "large" request for 536875008 bytes, total sbrk() is 217088 bytes at mem.pl line 6.
+4  A: 

This is not a Perl-specific issue, but rather one related to cygwin. You can raise memory allocation with ulimit.

What version of git are you using? If you're not on the latest version, this might be an inefficiency that has been fixed with the latest version (e.g. looping through a very large file with foreach rather than while, as google suggests when I did a quick search.)

Ether
git --version gives me 1.6.5.1.1367.gcd48 and I'm using the latest version of msysgit http://code.google.com/p/msysgit/ ulimit output is already 'unlimited' :S
Charles Ma
+5  A: 

Have you tried increasing overall Cygwin's usable memory?

That message shows Perl was already up to 130 MiB (total sbrk()) and then tried to request a further 256MiB which failed.

From http://www.perlmonks.org/?node%5Fid=541750

By default no Cygwin program can allocate more than 384 MB of memory 
(program+data). You should not need to change this default in most 
circumstances. However, if you need to use more real or virtual 
memory in your machine you may add an entry in the either the 
HKEY_LOCAL_MACHINE (to change the limit for all users) or
HKEY_CURRENT_USER (for just the current user) section of the registry.

Add the DWORD value heap_chunk_in_mb and set it to the desired 
memory limit in decimal MB. It is preferred to do this in Cygwin 
using the regtool program included in the Cygwin package. (For 
more information about regtool or the other Cygwin utilities, 
see the Section called Cygwin Utilities in Chapter 3 or use 
each the --help option of each util.) You should always be 
careful when using regtool since damaging your system registry
can result in an unusable system. 
Vinko Vrsalovic
I've followed these instructions to change the memory size http://www.cygwin.com/cygwin-ug-net/setup-maxmem.htmlusing the sample program to test for memory allocation shows 1536MB so it should be enough memory. That makes me think that the issue is with perl :S
Charles Ma
The error shows it's failing to allocate more than 384MiB, so it seems your change has not been correctly done. Have you a) verified you can actually allocate the 1.5GiB with the sample program in that manual page?, b) verified that Perl still fails when allocating 384MiB (and not when allocating more than 1.5GiB)? and c) Restarted the machine after the change (even if the instructions do not require it)?
Vinko Vrsalovic
Interesting...I was able to malloc 1.5GB of memory in C, but not malloc over 384MB of memory in perl
Charles Ma
Hmmm, maybe your test is trying to allocate contiguous memory (which is scarcer)? Anyways, there are some Google hits for Perl 384 MB and some of them refer to this problem, Perl can only allocate this amount of memory. Sadly, I haven't found a solution.
Vinko Vrsalovic
Thanks for your help anyway, I'm still looking for a solution for this issue, but for now I'm temporarily switching back to svn on windows
Charles Ma
+1  A: 

Solution with maximizing Cygwin memory actually does not work.

Currently there are two problems with Git on Windows:

  1. Packs more than 2G are hardly supported by either MsysGit and Cygwin git
  2. Cygwin default memory amount is too small
  3. 32bit Git is problemistic

What have I done step by step:

I moved my git repo to Unix machine, set next configs:

[pack]
        threads = 2
        packSizeLimit = 2G
        windowMemory = 512M

After that I made git gc and all packs were rebuilded to 2G ones.

Double checked that MsysGit is not installed on Windows machine, other way perl from MsysGit may be used.

Moved this repo back to windows machine and raised Cygwin memory limit:

regtool -i set /HKLM/Software/Cygwin/heap_chunk_in_mb 1536

It was important to set Cygwin memory higher than pack.windowMemory×pack.threads and not higher than 1.5G

So the first two problems are now solved. But the third is not.

Unfortunally it does not work on windows. During some repacks it sometimes crashes with out of memory. Even with threads = 1 and pack.windowMemory = 16M and max depth and delta set to 250.

Timofey Basanov