Very bad behavior of kswapd

[Laurent Chavet <lchavet@av.com>]

Try this (my example I've 2GB of ram)

turn all your swap off

dd about 15% of the size of your RAM:
dd if=/dev/zero of=/local/test count=300 bs=1000000

Run this program with SIZE about 95% of your RAM:

#include <stdlib.h>
#include <unistd.h>
#include <assert.h>

#define SIZE (1900 * 1024 * 1024)
int main()
{
  int i;
  char *p = malloc(SIZE);
  assert (p != NULL);
  for (i = 0; i < SIZE; i++)
 p[i] = 1;
  printf ("done %p\n", p);

  while (1)
  {
 sleep (60);
  }
  return 0;
}


Watch top: when this program needs the memory that kswapd keep in cache they go
both at 100% cpu (on SMP) but still the size of the program only grows at about
100KB/s, why is kswapd releasing it so slowly and taking so much CPU ?

Laurent Chavet