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User-Agent: Mozilla/4.77 [en] (X11; U; Linux 2.2.19-6.2.1smp i686)

Description of problem:
Running 2.4.3-12enterprise I'm seeing fairly reproducible hangs on heavy
memory usage.  The exact point of failure is not reproducible though the
mode of failure is consistent. 

How reproducible:
Always

Steps to Reproduce:
Attempting to simulate load on the memory system using the c program below:

#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>
#include <string.h>

/* want to stress memory allocation and deallocation, preferably while
 * many other tests are going in the background
 */


#define MB (1024 * 1024)

/* Sets maximum number of 1MB blocks to try to allocate */
/* Currently fixed to 256GB total */
#define MAX 2100


int main (int argc, char **argv) {
  struct timeval pre,post;
  int i;
  long TotalTime;
  void *MemBlocks[MAX];
  long TimeDiff;
  for (;;) {
    /* allocate */
    i=0;
    TotalTime = 0;
    gettimeofday(&pre, NULL);
    while ( (i < MAX) && ((MemBlocks[i] = malloc(MB)) != NULL)) {
      memset(MemBlocks[i],0,MB); /* write to memory to force the grab,
otherwise it's a lazy grab in the kernel and won't be really allocated */
      gettimeofday(&post, NULL);
      TimeDiff = ((post.tv_sec - pre.tv_sec) * 1000000);
      if (TimeDiff) {
	TimeDiff -= (pre.tv_usec - post.tv_usec);
      } else {
	TimeDiff = post.tv_usec - pre.tv_usec;
      }
      printf("Allocation of block %i succeeded and took %ld usec\n",i,
TimeDiff);
      TotalTime += TimeDiff;
      i++;
      gettimeofday(&pre, NULL);
    }

    printf("Allocation of block %d failed. Deallocating all memory.\n",i);
    printf("Total of %ld usec spent in allocation\n",TotalTime);
    printf("Average of %ld usec/MB\n",TotalTime/i);
    fflush(stdout);
    sleep (5);

    /* deallocate */
    i--;
    for (; i>=0; i--) {
      free(MemBlocks[i]);
    }
    printf("Done freeing, pausing before starting again.\n");
    fflush(stdout);
    sleep (5);


  }

  return 0;
}

I'm running two instances of the resulting program with the designed effect
of taking me deep into swap. I have 128MB of ram and 6 GB of swap enabled
as a 2gb swap partition and 2 2gb swap files. 

 



	

Actual Results:  Somewhere in the allocation loop, so far seen with both
instances of the above code having allocated more than 1gb, the system
hangs. I have seen both instances cycle once through allocation and
deallocation and then fail in the second allocation loop.

Additional info:

The one bit of consistency I've seen so far is an alt-sysrq induced 
mem-info has consistently shown 
Free Pages:  1396kB (0 kB High Mem)
The first memory line =512 kB   (seen once as 2=256kb and the rest as
1=512kB)
The second consistenly totals 884kB