LinuxQuestions.org - [SOLVED] mmap is failing. Is there a setting to correct this.

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mmap is failing. Is there a setting to correct this.

I have a new linux mint system with 32 GB of ram.

The following program fails with message
commit failed i=32758
However if I try to allocate 16 GB directly it succeeds. Is there a limit on the number of mmapped pages and where can I increase this limit.
I am using something like below to allocate a separate page for each pointer in my program followed by a non committed page so that I can track down a buffer overflow in my program. So I need to do separate commits and not allocate a single 16 GB block.

Code:

#include <stdio.h>

#include <sys/mman.h>



int main()

{

        char* pt = (char*)mmap( 0, 2*2*1024LU*1024LU*4096LU, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0 );

        for( int i=0;i<2*1024*1024;i++ ){

                if( mmap( pt, 10, PROT_READ|PROT_WRITE, MAP_FIXED|MAP_PRIVATE|MAP_ANONYMOUS, 0, 0 )==(void*)-1 ){

                        printf( "commit failed i=%u\n", i );

                        return 0;

                }

                *pt = 1;

                pt += 4096*2;

        }

        return 0;

}

I ran across this:

http://www.enchantedage.com/node/235

This indicates the limit is in /proc/sys/vm/max_map_count

On my system (I have only 8GB ram), the default value is 65530.

You should be able to change the limit permanently in sysctl.conf (parameter would be vm.max_map_count)

BTW, just a nit, but index "i" is declared to be an int, yet in the format you used it is treated as unsigned int.

It worked.
Thank you jpollard. You are such a great help.
Thanks for the nit also.