Subject: Re: mprotect() failed: Cannot allocate memory
From: Peter Zijlstra <peterz@infradead.org>
To: =?UTF-8?Q?Pawe=C5=82?= Sikora <pluto@agmk.net>
Cc: libc-help@sourceware.org, linux-kernel@vger.kernel.org
In-Reply-To: <201004210105.20942.pluto@agmk.net>
References: <201004210105.20942.pluto@agmk.net>
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Date: Wed, 21 Apr 2010 12:16:50 +0200
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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.

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