memory allocation problems

memory allocation problems

[majer]

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  Hi. Im hoping someone on here can help me out. I posted something
  similar to this back in June 2000 and was hoping the 2.4 kernel
  would provide a fix.

  Essentially, the problem can be summarized to be that on a machine
  with ample ram (2G, 4G, etc), I am unable to malloc a gig if I ask 
  for the memory in small ( <= 128k) chunks. I've enclosed some results 
  and a little program which was put together to demonstrate the problems
  we're having.  All of the failures seem to occur around 930MB.

  I'm more than happy to try any tunings, patches, etc and my 
  time is at your disposal.

  Thanks,

  Karl

----
        Karl Majer                          majerNO@SPAMendeca.com              
        Sr Systems Architect                617 577 7999 xt 251                

 "Think for yourselves and let others enjoy the privilege to do so, too."
						     --Voltaire

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#include<stdio.h>
#include<unistd.h>
#include<stdlib.h>
#include<errno.h>

unsigned int i,num,bites,total,delay=0;
char **memhog;

int main(int argc,char *argv[]){

  if(argc!=4){
    fprintf(stderr,"usage: %s [# of chunks] [bytes per chunk] [delay in sec]\n",argv[0]);
    return(1);
  } 

  num=atoi(argv[1]);
  bites=atoi(argv[2]);
  delay=atoi(argv[3]);

  memhog=malloc(sizeof(char*) * num); 
  if(!memhog){
    fprintf(stderr,"malloc error %s\n",strerror(errno));  
    exit(1);
  }

  for(i=0;i<num;i++){
    *memhog=malloc(bites);
    if(!*memhog){
      fprintf(stderr,"malloc error %s\n",strerror(errno));  
      exit(1);
    }
    total+=bites;
    printf("#%u (%X) (%X) allocated %u bytes total.\n",i,memhog,*memhog,total);
    memhog++;
    sleep(delay);
  }  

 return(0);
} 
  


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  The fields are: 
  Iteration, Addr of ptr, Addr stored by ptr, alloc'd mem

  size: 4096
  #228852 (401F07D8) (3FFFC948) allocated 937381888 bytes total.
  #228853 (401F07DC) (3FFFD950) allocated 937385984 bytes total.
  malloc error Cannot allocate memory
  
  size: 8192
  #114536 (40180DA8) (3FFF94E8) allocated 938287104 bytes total.
  #114537 (40180DAC) (3FFFB4F0) allocated 938295296 bytes total.
  malloc error Cannot allocate memory
   
  size: 16384
  #57294 (40148F40) (3FFF1818) allocated 938721280 bytes total.
  #57295 (40148F44) (3FFF5820) allocated 938737664 bytes total.
  malloc error Cannot allocate memory
  
  size: 32768
  #28653 (4012CFBC) (3FFE9910) allocated 938934272 bytes total.
  #28654 (4012CFC0) (3FFF1918) allocated 938967040 bytes total.
  malloc error Cannot allocate memory
  
  size: 65536
  #14325 (805797C) (3FFC5958) allocated 938868736 bytes total.
  #14326 (8057980) (3FFD5960) allocated 938934272 bytes total.
  #14327 (8057984) (3FFE5968) allocated 938999808 bytes total.
  malloc error Cannot allocate memory
  
  size: 131072
  #8186 (8051990) (3FF9F980) allocated 1073086464 bytes total.
  #8187 (8051994) (3FFBF988) allocated 1073217536 bytes total.
  malloc error Cannot allocate memory
  
  size: 262144
  #4094 (804D9A0) (37FD39A0) allocated 1073479680 bytes total.
  #4095 (804D9A4) (380139A8) allocated 1073741824 bytes total.
  success
   

Re: memory allocation problems

[Hugh Dickins]

On Fri, 6 Apr 2001, Wayne Whitney wrote:
> 
> As was pointed out to me in January, another solution for i386 would be to
> fix a maximum stack size and have the mmap() allocations grow downward
> from the "top" of the stack (3GB - max stack size).  I'm not sure why that
> is not currently done.

I'd be interested in the answer to that too.  Typically, the memory
layout has ELF text at the lowest address, starting at 0x08048000 -
which is a curious place to put it, until you realize that if you
place the stack below it, you can use (in a typical small program)
just one page table for stack + text + data (then another for mmaps
and shared libs from 3GB down): two page tables instead of present three.

Hugh

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