# slabuse2.stp
# This script captures the stack back trace for a each slab object
# once a threshold active objects is reached for the object.
# The following would track allocations for ext3_inode_cache and
# dentry_cache objects whenever the script observes slab object 
# allocations exceeding slab object frees by  100
#
# stap  -g slabuse2.stp "ext3_inode_cache dentry_cache" 100
#
# slabuse2.stp is for use on older versions of systemtap, 0.5.12
# which do not have the tokenize() functions

/* the collect_data variable is set when problem condition occurs */
global name_of_interest
global alloc_active

global stats, stacks

probe kernel.function("kmem_cache_alloc") {
  name = kernel_string($cachep->name)
  count_of_interest = name_of_interest[name]
  if (count_of_interest > 0) {
    alloc_active[name]++
    if (alloc_active[name] >= name_of_interest[name]) {
      exec = execname()
      stats[exec, name] <<< 1
      stacks[exec, name, backtrace()] <<< 1
    }
  }
}

probe kernel.function("kmem_cache_free") {
  name = kernel_string($cachep->name)
  if (alloc_active[name]) alloc_active[name]--
}

probe begin {
  /* tokenize argument for list of allocations to watch */
  /* argument is of the form:  "ext3_inode_cache dentry_cache" 100 */
  name = tokenize(@1, " ")
  count = $2
  while (name != "" ) {
    name_of_interest[name] = count
    name = tokenize("", " ")
  }
}

probe end {
  printf("Number of slab allocations by process and slab name\n")
  foreach ([exec, name] in stats- limit 20) {
    printf("%s, %s:\t%d\n", exec, name, @count(stats[exec, name]))
  }

  printf("\nBacktrace of processes when allocating\n")
  foreach ([exec, cache, bt] in stacks- limit 20) {
    printf("Exec: %s Slab name: %s  Count: %d\n",
       exec, cache, @count(stacks[exec, cache, bt]))
         print_stack(bt)
         printf("\n-------------------------------------------------------\n\n")
  }
}

/*
 * tokenize - Given a string and a token delimiter,
 *            return the next token in the string
 * input  String to tokenize. If NULL, returns the next token in the
 *        string passed in the previous call to tokenize().
 * delim  Token delimiter. Note this is a string, but only the first
 *        character is used as the delimiter.
 */
function tokenize:string(input:string, delim:string)
%{ /* pure */
	static char str[MAXSTRINGLEN];
	static char *str_start;
	char *token = NULL;

	if (THIS->input[0]) {
		strncpy(str, THIS->input, MAXSTRINGLEN);
		str_start = &str[0];
	}
	token = strsep(&str_start, THIS->delim);
	if (token)
		strncpy (THIS->__retvalue, token, MAXSTRINGLEN);
%}