mm/oom_kill.c - linux-mtk - Git at Google

 /*
  *  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;
 	}

 	/*
 	 * 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);

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

 	/*
 	 * 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) {
 			if (!points)
 				points = 1;
 			points <<= p->oomkilladj;
 		} else
 			points >>= -(p->oomkilladj);
 	}

 #ifdef DEBUG
 	printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
 	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;
 	int node;

 	nodes_clear(nodes);
 	/* node has memory ? */
 	for_each_online_node(node)
 		if (NODE_DATA(node)->node_present_pages)
 			node_set(node, nodes);

 	for (z = zonelist->zones; *z; z++)
 		if (cpuset_zone_allowed_softwall(*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, int verbose)
 {
 	if (is_init(p)) {
 		WARN_ON(1);
 		printk(KERN_WARNING "tried to kill init!\n");
 		return;
 	}

 	if (!p->mm) {
 		WARN_ON(1);
 		printk(KERN_WARNING "tried to kill an mm-less task!\n");
 		return;
 	}

 	if (verbose)
 		printk(KERN_ERR "Killed process %d (%s)\n", 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)
 {
 	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;

 	/*
 	 * Don't kill the process if any threads are set to OOM_DISABLE
 	 */
 	do_each_thread(g, q) {
 		if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
 			return 1;
 	} while_each_thread(g, q);

 	__oom_kill_task(p, 1);

 	/*
 	 * kill all processes that share the ->mm (i.e. all threads),
 	 * but are in a different thread group. Don't let them have access
 	 * to memory reserves though, otherwise we might deplete all memory.
 	 */
 	do_each_thread(g, q) {
 		if (q->mm == mm && q->tgid != p->tgid)
 			force_sig(SIGKILL, q);
 	} 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, 0);
 		return 0;
 	}

 	printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
 					message, 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))
 			return 0;
 	}
 	return oom_kill_task(p);
 }

 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\n",
 			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\n");
 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...\n");
 		}

 		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);
 }
	/*
	* 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;
	}

	/*
	* 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);

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

	/*
	* 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) {
	if (!points)
	points = 1;
	points <<= p->oomkilladj;
	} else
	points >>= -(p->oomkilladj);
	}

	#ifdef DEBUG
	printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
	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;
	int node;

	nodes_clear(nodes);
	/* node has memory ? */
	for_each_online_node(node)
	if (NODE_DATA(node)->node_present_pages)
	node_set(node, nodes);

	for (z = zonelist->zones; *z; z++)
	if (cpuset_zone_allowed_softwall(*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, int verbose)
	{
	if (is_init(p)) {
	WARN_ON(1);
	printk(KERN_WARNING "tried to kill init!\n");
	return;
	}

	if (!p->mm) {
	WARN_ON(1);
	printk(KERN_WARNING "tried to kill an mm-less task!\n");
	return;
	}

	if (verbose)
	printk(KERN_ERR "Killed process %d (%s)\n", 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)
	{
	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;

	/*
	* Don't kill the process if any threads are set to OOM_DISABLE
	*/
	do_each_thread(g, q) {
	if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
	return 1;
	} while_each_thread(g, q);

	__oom_kill_task(p, 1);

	/*
	* kill all processes that share the ->mm (i.e. all threads),
	* but are in a different thread group. Don't let them have access
	* to memory reserves though, otherwise we might deplete all memory.
	*/
	do_each_thread(g, q) {
	if (q->mm == mm && q->tgid != p->tgid)
	force_sig(SIGKILL, q);
	} 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, 0);
	return 0;
	}

	printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
	message, 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))
	return 0;
	}
	return oom_kill_task(p);
	}

	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\n",
	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\n");
	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...\n");
	}

	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);
	}