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SubjectRe: Memory issues with Opteron 6220
On 2012-02-09 09:33, Ingo Molnar wrote:
> * Anders Ossowicki<aowi@novozymes.com> wrote:
>> Hey,
>>
>> We're seeing unexpected slowdowns and other memory issues with a new system.
>> Enough to render it unusable. For example:
>>
>> Error: open3: fork failed: Cannot allocate memory
>>
>> at times where there's no real memory pressure:
>> total used free shared buffers cached
>> Mem: 132270720 131942388 328332 0 299768 103334420
>> -/+ buffers/cache: 28308200 103962520
>> Swap: 7811068 13760 7797308
>>
>> [...]
Anders' co-worker here.. below C-code (Summary: for -t processes that
repeatedly
allocates and dallocates 2GB of memory) can excersize the bug
pretty frequently using -t 32 on this machine. On the other 128GB
machine it can run without issues.

It actually ended up toasting the machine:
jk@nysvin:~$ ./foo -t 32
-bash: fork: Cannot allocate memory
jk@nysvin:~$ w
-bash: fork: Cannot allocate memory
jk@nysvin:~$ top
-bash: fork: Cannot allocate memory
jk@nysvin:~$ ls
-bash: fork: Cannot allocate memory

I dont know what to conclude.

jk@nysvin:~$ ./foo -t 32
Upper bound: 1953 MB
malloc(1953) MB failed. iterations: 6
malloc(1953) MB failed. iterations: 2
malloc(1953) MB failed. iterations: 8

foo.c
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/wait.h>

void worker(void)
{
long long i;
char *p;
int action;
int mult = 500000;
int size = mult * 4096;
fprintf(stderr,"Upper bound: %lu MB\n",(long int) (size/1024/1024));
for (i=0; ; i++) {
action = i%2;
switch(action) {
case 0:
p = malloc(size);
if (!p){
fprintf(stderr,"malloc(%lu) MB failed. iterations:
%lli\n", (long int)size/1024/1024,i);
exit(1);
}
break;
case 1:
free(p);
break;
}
}
}

void usage(const char *cmd)
{
fprintf(stderr,"Usage: %s [-t numthreads]\n", cmd);
exit(1);
}

int main(int argc, char **argv)
{
int c, i;
int nproc = sysconf(_SC_NPROCESSORS_ONLN);


while ((c = getopt(argc, argv, "t:")) != EOF) {
switch (c) {
case 't':
nproc = strtol(optarg, 0, 0);
break;
default:
usage(argv[0]);
}
}

//printf("forking %d children\n", nproc);
for (i=0; i < nproc; i++) {
switch(fork()) {
case -1:
fprintf(stderr,"fork: %s\n", strerror(errno));
exit(1);
case 0: /* child */
worker();
exit(0);
default: /* parent */
/* nothing */
break;
}
}

for (i=0; i < nproc; i++) {
int x, p;
p = wait(&x);
}

return 0;
}

Can also be found here: http://shrek.krogh.cc/~jesper/foo.c

--
Jesper Krogh


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