/*
   *  linux/mm/oom_kill.c
   * 
   *  Copyright (C)  1998,2000  Rik van Riel
   *	Thanks go out to Claus Fischer for some serious inspiration and
   *	for goading me into coding this file...
   *
   *  The routines in this file are used to kill a process when

   *  we're seriously out of memory. This gets called from __alloc_pages()
   *  in mm/page_alloc.c when we really run out of memory.

   *
   *  Since we won't call these routines often (on a well-configured
   *  machine) this file will double as a 'coding guide' and a signpost
   *  for newbie kernel hackers. It features several pointers to major
   *  kernel subsystems and hints as to where to find out what things do.
   */

  #include <linux/oom.h>

  #include <linux/mm.h>
  #include <linux/sched.h>
  #include <linux/swap.h>
  #include <linux/timex.h>
  #include <linux/jiffies.h>

  #include <linux/cpuset.h>

  #include <linux/module.h>
  #include <linux/notifier.h>

  int sysctl_panic_on_oom;

  /* #define DEBUG */
  
  /**

   * badness - calculate a numeric value for how bad this task has been

   * @p: task struct of which task we should calculate

   * @uptime: current uptime in seconds

   *
   * The formula used is relatively simple and documented inline in the
   * function. The main rationale is that we want to select a good task
   * to kill when we run out of memory.
   *
   * Good in this context means that:
   * 1) we lose the minimum amount of work done
   * 2) we recover a large amount of memory
   * 3) we don't kill anything innocent of eating tons of memory
   * 4) we want to kill the minimum amount of processes (one)
   * 5) we try to kill the process the user expects us to kill, this
   *    algorithm has been meticulously tuned to meet the principle
   *    of least surprise ... (be careful when you change it)
   */
  
  unsigned long badness(struct task_struct *p, unsigned long uptime)
  {
  	unsigned long points, cpu_time, run_time, s;

  	struct mm_struct *mm;
  	struct task_struct *child;

  	task_lock(p);
  	mm = p->mm;
  	if (!mm) {
  		task_unlock(p);

  		return 0;

  	}

  
  	/*

  	 * swapoff can easily use up all memory, so kill those first.
  	 */
  	if (p->flags & PF_SWAPOFF)
  		return ULONG_MAX;
  
  	/*

  	 * The memory size of the process is the basis for the badness.
  	 */

  	points = mm->total_vm;
  
  	/*
  	 * After this unlock we can no longer dereference local variable `mm'
  	 */
  	task_unlock(p);

  
  	/*
  	 * Processes which fork a lot of child processes are likely

  	 * a good choice. We add half the vmsize of the children if they

  	 * have an own mm. This prevents forking servers to flood the

  	 * machine with an endless amount of children. In case a single
  	 * child is eating the vast majority of memory, adding only half
  	 * to the parents will make the child our kill candidate of choice.

  	 */

  	list_for_each_entry(child, &p->children, sibling) {
  		task_lock(child);
  		if (child->mm != mm && child->mm)
  			points += child->mm->total_vm/2 + 1;
  		task_unlock(child);

  	}
  
  	/*
  	 * CPU time is in tens of seconds and run time is in thousands
           * of seconds. There is no particular reason for this other than
           * that it turned out to work very well in practice.
  	 */
  	cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
  		>> (SHIFT_HZ + 3);
  
  	if (uptime >= p->start_time.tv_sec)
  		run_time = (uptime - p->start_time.tv_sec) >> 10;
  	else
  		run_time = 0;
  
  	s = int_sqrt(cpu_time);
  	if (s)
  		points /= s;
  	s = int_sqrt(int_sqrt(run_time));
  	if (s)
  		points /= s;
  
  	/*
  	 * Niced processes are most likely less important, so double
  	 * their badness points.
  	 */
  	if (task_nice(p) > 0)
  		points *= 2;
  
  	/*
  	 * Superuser processes are usually more important, so we make it
  	 * less likely that we kill those.
  	 */
  	if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
  				p->uid == 0 || p->euid == 0)
  		points /= 4;
  
  	/*
  	 * We don't want to kill a process with direct hardware access.
  	 * Not only could that mess up the hardware, but usually users
  	 * tend to only have this flag set on applications they think
  	 * of as important.
  	 */
  	if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
  		points /= 4;
  
  	/*

  	 * If p's nodes don't overlap ours, it may still help to kill p
  	 * because p may have allocated or otherwise mapped memory on
  	 * this node before. However it will be less likely.
  	 */
  	if (!cpuset_excl_nodes_overlap(p))
  		points /= 8;
  
  	/*

  	 * Adjust the score by oomkilladj.
  	 */
  	if (p->oomkilladj) {
  		if (p->oomkilladj > 0)
  			points <<= p->oomkilladj;
  		else
  			points >>= -(p->oomkilladj);
  	}
  
  #ifdef DEBUG
  	printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points
  ",
  	p->pid, p->comm, points);
  #endif
  	return points;
  }
  
  /*

   * Types of limitations to the nodes from which allocations may occur
   */
  #define CONSTRAINT_NONE 1
  #define CONSTRAINT_MEMORY_POLICY 2
  #define CONSTRAINT_CPUSET 3
  
  /*
   * Determine the type of allocation constraint.
   */
  static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
  {
  #ifdef CONFIG_NUMA
  	struct zone **z;
  	nodemask_t nodes = node_online_map;
  
  	for (z = zonelist->zones; *z; z++)
  		if (cpuset_zone_allowed(*z, gfp_mask))

  			node_clear(zone_to_nid(*z), nodes);

  		else
  			return CONSTRAINT_CPUSET;
  
  	if (!nodes_empty(nodes))
  		return CONSTRAINT_MEMORY_POLICY;
  #endif
  
  	return CONSTRAINT_NONE;
  }
  
  /*

   * Simple selection loop. We chose the process with the highest
   * number of 'points'. We expect the caller will lock the tasklist.
   *
   * (not docbooked, we don't want this one cluttering up the manual)
   */

  static struct task_struct *select_bad_process(unsigned long *ppoints)

  {

  	struct task_struct *g, *p;
  	struct task_struct *chosen = NULL;
  	struct timespec uptime;

  	*ppoints = 0;

  
  	do_posix_clock_monotonic_gettime(&uptime);

  	do_each_thread(g, p) {
  		unsigned long points;

  		/*
  		 * skip kernel threads and tasks which have already released
  		 * their mm.
  		 */

  		if (!p->mm)
  			continue;

  		/* skip the init task */
  		if (is_init(p))

  			continue;

  		/*

  		 * This task already has access to memory reserves and is
  		 * being killed. Don't allow any other task access to the
  		 * memory reserve.
  		 *
  		 * Note: this may have a chance of deadlock if it gets
  		 * blocked waiting for another task which itself is waiting
  		 * for memory. Is there a better alternative?
  		 */
  		if (test_tsk_thread_flag(p, TIF_MEMDIE))
  			return ERR_PTR(-1UL);
  
  		/*

  		 * This is in the process of releasing memory so wait for it

  		 * to finish before killing some other task by mistake.

  		 *
  		 * However, if p is the current task, we allow the 'kill' to
  		 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
  		 * which will allow it to gain access to memory reserves in
  		 * the process of exiting and releasing its resources.

  		 * Otherwise we could get an easy OOM deadlock.

  		 */

  		if (p->flags & PF_EXITING) {
  			if (p != current)
  				return ERR_PTR(-1UL);

  			chosen = p;
  			*ppoints = ULONG_MAX;

  		}

  		if (p->oomkilladj == OOM_DISABLE)
  			continue;

  
  		points = badness(p, uptime.tv_sec);

  		if (points > *ppoints || !chosen) {

  			chosen = p;

  			*ppoints = points;

  		}

  	} while_each_thread(g, p);

  	return chosen;
  }
  
  /**

   * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
   * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
   * set.

   */

  static void __oom_kill_task(struct task_struct *p, const char *message)

  {

  	if (is_init(p)) {

  		WARN_ON(1);
  		printk(KERN_WARNING "tried to kill init!
  ");
  		return;
  	}

  	if (!p->mm) {

  		WARN_ON(1);
  		printk(KERN_WARNING "tried to kill an mm-less task!
  ");

  		return;
  	}

  
  	if (message) {
  		printk(KERN_ERR "%s: Killed process %d (%s).
  ",

  				message, p->pid, p->comm);

  	}

  
  	/*
  	 * We give our sacrificial lamb high priority and access to
  	 * all the memory it needs. That way it should be able to
  	 * exit() and clear out its resources quickly...
  	 */
  	p->time_slice = HZ;
  	set_tsk_thread_flag(p, TIF_MEMDIE);
  
  	force_sig(SIGKILL, p);
  }

  static int oom_kill_task(struct task_struct *p, const char *message)

  {

  	struct mm_struct *mm;

  	struct task_struct *g, *q;

  	mm = p->mm;
  
  	/* WARNING: mm may not be dereferenced since we did not obtain its
  	 * value from get_task_mm(p).  This is OK since all we need to do is
  	 * compare mm to q->mm below.
  	 *
  	 * Furthermore, even if mm contains a non-NULL value, p->mm may
  	 * change to NULL at any time since we do not hold task_lock(p).
  	 * However, this is of no concern to us.
  	 */

  	if (mm == NULL)

  		return 1;

  	__oom_kill_task(p, message);

  	/*
  	 * kill all processes that share the ->mm (i.e. all threads),
  	 * but are in a different thread group
  	 */
  	do_each_thread(g, q)
  		if (q->mm == mm && q->tgid != p->tgid)

  			__oom_kill_task(q, message);

  	while_each_thread(g, q);

  	return 0;

  }

  static int oom_kill_process(struct task_struct *p, unsigned long points,
  		const char *message)

  {

  	struct task_struct *c;
  	struct list_head *tsk;

  	/*
  	 * If the task is already exiting, don't alarm the sysadmin or kill
  	 * its children or threads, just set TIF_MEMDIE so it can die quickly
  	 */
  	if (p->flags & PF_EXITING) {
  		__oom_kill_task(p, NULL);
  		return 0;
  	}
  
  	printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li"
  			" and children.
  ", p->pid, p->comm, points);

  	/* Try to kill a child first */
  	list_for_each(tsk, &p->children) {
  		c = list_entry(tsk, struct task_struct, sibling);
  		if (c->mm == p->mm)
  			continue;

  		if (!oom_kill_task(c, message))
  			return 0;

  	}

  	return oom_kill_task(p, message);

  }

  static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
  
  int register_oom_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_register(&oom_notify_list, nb);
  }
  EXPORT_SYMBOL_GPL(register_oom_notifier);
  
  int unregister_oom_notifier(struct notifier_block *nb)
  {
  	return blocking_notifier_chain_unregister(&oom_notify_list, nb);
  }
  EXPORT_SYMBOL_GPL(unregister_oom_notifier);

  /**

   * out_of_memory - kill the "best" process when we run out of memory

   *
   * If we run out of memory, we have the choice between either
   * killing a random task (bad), letting the system crash (worse)
   * OR try to be smart about which process to kill. Note that we
   * don't have to be perfect here, we just have to be good.
   */

  void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)

  {

  	struct task_struct *p;

  	unsigned long points = 0;

  	unsigned long freed = 0;
  
  	blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
  	if (freed > 0)
  		/* Got some memory back in the last second. */
  		return;

  	if (printk_ratelimit()) {

  		printk(KERN_WARNING "%s invoked oom-killer: "
  			"gfp_mask=0x%x, order=%d, oomkilladj=%d
  ",
  			current->comm, gfp_mask, order, current->oomkilladj);

  		dump_stack();

  		show_mem();
  	}

  	cpuset_lock();

  	read_lock(&tasklist_lock);

  
  	/*
  	 * Check if there were limitations on the allocation (only relevant for
  	 * NUMA) that may require different handling.
  	 */
  	switch (constrained_alloc(zonelist, gfp_mask)) {
  	case CONSTRAINT_MEMORY_POLICY:

  		oom_kill_process(current, points,

  				"No available memory (MPOL_BIND)");
  		break;
  
  	case CONSTRAINT_CPUSET:

  		oom_kill_process(current, points,

  				"No available memory in cpuset");
  		break;
  
  	case CONSTRAINT_NONE:

  		if (sysctl_panic_on_oom)
  			panic("out of memory. panic_on_oom is selected
  ");

  retry:

  		/*
  		 * Rambo mode: Shoot down a process and hope it solves whatever
  		 * issues we may have.
  		 */
  		p = select_bad_process(&points);

  		if (PTR_ERR(p) == -1UL)
  			goto out;

  		/* Found nothing?!?! Either we hang forever, or we panic. */
  		if (!p) {
  			read_unlock(&tasklist_lock);
  			cpuset_unlock();
  			panic("Out of memory and no killable processes...
  ");
  		}

  		if (oom_kill_process(p, points, "Out of memory"))

  			goto retry;
  
  		break;
  	}

  out:

  	read_unlock(&tasklist_lock);

  	cpuset_unlock();

  
  	/*
  	 * Give "p" a good chance of killing itself before we

  	 * retry to allocate memory unless "p" is current

  	 */

  	if (!test_thread_flag(TIF_MEMDIE))

  		schedule_timeout_uninterruptible(1);

  }