mprotect() failed: Cannot allocate memory

[Peter Zijlstra]

On Wed, 2010-04-21 at 01:05 +0200, Paweł Sikora wrote:
> hi,
> 
> i'm trying to debug an ugly application with ElectricFence.
> in fact, on x86-64 box with 8GB ram and 16GB swap i'm getting following error:
> 
> "ElectricFence Exiting: mprotect() failed: Cannot allocate memory"
> 
> the program has been compiled with gcc-4.5, glibc-2.11.1, kernel-2.6.32.
> did you ever come across such (kernel/glibc) limitations?
> 
> here's a simple testcase which triggs -ENOMEM in mprotect().

You probably depleted the max map count, see:
  /proc/sys/vm/max_map_count

We have a limit on the number of maps you can have, those mprotect()
calls split you maps like crazy, see also /proc/$pid/maps.

eg. change your second test program to include something like:

  char buf[128];
  snprintf(buf, sizeof(buf), "cat /proc/%d/maps", (int)getpid());
  system(buf);

at the end after lowering your NN count to fit, and observe the result
of those mprotect() calls.