Hari's Technical Space

1. What can I use this for?

• Test swap
• Test behaviors on a machine when there is little memory available

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2. Usage

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Installation

cd /tmp
vim memtest.c
<enter the contents in the file and save it>
vim Makefile
<enter the contents in the file and save it>
sudo make install

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Makefile

all: memtest.c
$(CC) memtest.c -o memtest

install: memtest
install -m 0755 memtest $(PREFIX)/bin/

clean:
rm -rf *o memtest

memtest.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <stdbool.h>
#include <unistd.h>

#if defined(_SC_PHYS_PAGES) && defined(_SC_AVPHYS_PAGES) && defined(_SC_PAGE_SIZE)
#define MEMORY_PERCENTAGE
#endif

#ifdef MEMORY_PERCENTAGE
size_t getTotalSystemMemory(){
long pages = sysconf(_SC_PHYS_PAGES);
long page_size = sysconf(_SC_PAGE_SIZE);
return pages * page_size;
}

size_t getFreeSystemMemory(){
long pages = sysconf(_SC_AVPHYS_PAGES);
long page_size = sysconf(_SC_PAGE_SIZE);
return pages * page_size;
}
#endif

bool eat(long total,int chunk){
long i;
for(i=0;i<total;i+=chunk){
short *buffer=malloc(sizeof(char)*chunk);
if(buffer==NULL){
return false;
}
memset(buffer,0,chunk);
}
return true;
}

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

#ifdef MEMORY_PERCENTAGE
printf(“Currently total memory: %zd\n”,getTotalSystemMemory());
printf(“Currently avail memory: %zd\n”,getFreeSystemMemory());
#endif

int i;
for(i=0;i<argc;i++){
char *arg=argv[i];
if(strcmp(arg, “-h”)==0 || strcmp(arg,”-?”)==0  || argc==1){
printf(“Usage: eatmemory <size>\n”);
printf(“Size can be specified in megabytes or gigabytes in the following way:\n”);
printf(“#          # Bytes      example: 1024\n”);
printf(“#M         # Megabytes  example: 15M\n”);
printf(“#G         # Gigabytes  example: 2G\n”);
#ifdef MEMORY_PERCENTAGE
printf(“#%%         # Percent    example: 50%%\n”);
#endif
printf(“\n”);
}else if(i>0){
int len=strlen(arg);
char unit=arg[len – 1];
long size=-1;
int chunk=1024;
if(!isdigit(unit) ){
if(unit==’M’ || unit==’G’){
arg[len-1]=0;
size=atol(arg) * (unit==’M’?1024*1024:1024*1024*1024);
}
#ifdef MEMORY_PERCENTAGE
else if (unit==’%’) {
size = (atol(arg) * (long)getFreeSystemMemory())/100;
}
#endif
else{
printf(“Invalid size format\n”);
exit(0);
}
}else{
size=atoi(arg);
}
printf(“Eating %ld bytes in chunks of %d…\n”,size,chunk);
if(eat(size,chunk)){
printf(“Done, press any key to free the memory\n”);
getchar();
}else{
printf(“ERROR: Could not allocate the memory”);
}
}
}

}

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Running

memtest <size>

Size is in number of bytes, megabytes or gigabytes.

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Examples

memtest 1024
memtest 10M
memtest 4G