enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
		unsigned long totalpages, const nodemask_t *nodemask,
		bool force_kill)
{
	if (task->exit_state)
		return OOM_SCAN_CONTINUE;
	if (oom_unkillable_task(task, NULL, nodemask))
		return OOM_SCAN_CONTINUE;

	/*
	 * This task already has access to memory reserves and is being killed.
	 * Don't allow any other task to have access to the reserves.
	 */
	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
		if (unlikely(frozen(task)))
			__thaw_task(task);
		if (!force_kill)
			return OOM_SCAN_ABORT;
	}
	if (!task->mm)
		return OOM_SCAN_CONTINUE;

	if (task->flags & PF_EXITING) {
		/*
		 * If task is current and is in the process of releasing memory,
		 * allow the "kill" to set TIF_MEMDIE, which will allow it to
		 * access memory reserves.  Otherwise, it may stall forever.
		 *
		 * The iteration isn't broken here, however, in case other
		 * threads are found to have already been oom killed.
		 */
		if (task == current)
			return OOM_SCAN_SELECT;
		else if (!force_kill) {
			/*
			 * If this task is not being ptraced on exit, then wait
			 * for it to finish before killing some other task
			 * unnecessarily.
			 */
			if (!(task->group_leader->ptrace & PT_TRACE_EXIT))
				return OOM_SCAN_ABORT;
		}
	}
	return OOM_SCAN_OK;
}

/**
 * oom_badness - heuristic function to determine which candidate task to kill
 * @p: task struct of which task we should calculate
 * @totalpages: total present RAM allowed for page allocation
 *
 * The heuristic for determining which task to kill is made to be as simple and
 * predictable as possible.  The goal is to return the highest value for the
 * task consuming the most memory to avoid subsequent oom failures.
 */
unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
			  const nodemask_t *nodemask, unsigned long totalpages)
{
	long points;
	long adj;

	if (oom_unkillable_task(p, memcg, nodemask))
		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	adj = (long)p->signal->oom_score_adj;
	if (adj == OOM_SCORE_ADJ_MIN) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + p->mm->nr_ptes +
		 get_mm_counter(p->mm, MM_SWAPENTS);

	task_unlock(p);

	/*
	 * Root processes get 3% bonus, just like the __vm_enough_memory()
	 * implementation used by LSMs.
	 */
	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
		adj -= 30;

	/* Normalize to oom_score_adj units */
	adj *= totalpages / 1000;
	points += adj;

	/*
	 * Never return 0 for an eligible task regardless of the root bonus and
	 * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
	 */
	return points > 0 ? points : 1;
}

enum oom_scan_t oom_scan_process_thread(struct task_struct *task,
		unsigned long totalpages, const nodemask_t *nodemask,
		bool force_kill)
{
	if (task->exit_state) {
#ifdef CONFIG_OOM_SCAN_WA_PREVENT_WRONG_SEARCH
		if (task->pid == task->tgid)
			return OOM_SCAN_SKIP_SEARCH_THREAD;
#endif
		return OOM_SCAN_CONTINUE;
	}
	if (oom_unkillable_task(task, NULL, nodemask))
		return OOM_SCAN_CONTINUE;

	/*
	 * This task already has access to memory reserves and is being killed.
	 * Don't allow any other task to have access to the reserves.
	 */
	if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
		if (unlikely(frozen(task)))
			__thaw_task(task);
		if (!force_kill)
			return OOM_SCAN_ABORT;
	}
	if (!task->mm)
		return OOM_SCAN_CONTINUE;

	/*
	 * If task is allocating a lot of memory and has been marked to be
	 * killed first if it triggers an oom, then select it.
	 */
	if (oom_task_origin(task))
		return OOM_SCAN_SELECT;

	if (task->flags & PF_EXITING && !force_kill) {
		/*
		 * If this task is not being ptraced on exit, then wait for it
		 * to finish before killing some other task unnecessarily.
		 */
		if (!(task->group_leader->ptrace & PT_TRACE_EXIT))
			return OOM_SCAN_ABORT;
	}
	return OOM_SCAN_OK;
}

/**
 * oom_badness - heuristic function to determine which candidate task to kill
 * @p: task struct of which task we should calculate
 * @totalpages: total present RAM allowed for page allocation
 * @memcg: task's memory controller, if constrained
 * @nodemask: nodemask passed to page allocator for mempolicy ooms
 *
 * The heuristic for determining which task to kill is made to be as simple and
 * predictable as possible.  The goal is to return the highest value for the
 * task consuming the most memory to avoid subsequent oom failures.
 */
unsigned long oom_badness(struct task_struct *p, struct mem_cgroup *memcg,
			  const nodemask_t *nodemask, unsigned long totalpages)
{
	long points;
	long adj;

	if (oom_unkillable_task(p, memcg, nodemask))
		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	/*
	 * Do not even consider tasks which are explicitly marked oom
	 * unkillable or have been already oom reaped or the are in
	 * the middle of vfork
	 */
	adj = (long)p->signal->oom_score_adj;
	if (adj == OOM_SCORE_ADJ_MIN ||
			test_bit(MMF_OOM_SKIP, &p->mm->flags) ||
			in_vfork(p)) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + get_mm_counter(p->mm, MM_SWAPENTS) +
		mm_pgtables_bytes(p->mm) / PAGE_SIZE;
	task_unlock(p);

	/* Normalize to oom_score_adj units */
	adj *= totalpages / 1000;
	points += adj;

	/*
	 * Never return 0 for an eligible task regardless of the root bonus and
	 * oom_score_adj (oom_score_adj can't be OOM_SCORE_ADJ_MIN here).
	 */
	return points > 0 ? points : 1;
}

enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
			struct task_struct *task, unsigned long totalpages)
{
	if (oom_unkillable_task(task, NULL, oc->nodemask))
		return OOM_SCAN_CONTINUE;

	/*
	 * This task already has access to memory reserves and is being killed.
	 * Don't allow any other task to have access to the reserves.
	 */
	if (!is_sysrq_oom(oc) && atomic_read(&task->signal->oom_victims))
		return OOM_SCAN_ABORT;

	/*
	 * If task is allocating a lot of memory and has been marked to be
	 * killed first if it triggers an oom, then select it.
	 */
	if (oom_task_origin(task))
		return OOM_SCAN_SELECT;

	return OOM_SCAN_OK;
}

/*
 * 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 int *ppoints,
		unsigned long totalpages, struct mem_cgroup *memcg,
		const nodemask_t *nodemask, bool force_kill)
{
	struct task_struct *g, *p;
	struct task_struct *chosen = NULL;
	*ppoints = 0;

	do_each_thread(g, p) {
		unsigned int points;

		if (p->exit_state)
			continue;
		if (oom_unkillable_task(p, memcg, nodemask))
			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)) {
			if (unlikely(frozen(p)))
				__thaw_task(p);
			if (!force_kill)
				return ERR_PTR(-1UL);
		}
		if (!p->mm)
			continue;

		if (p->flags & PF_EXITING) {
			/*
			 * If p is the current task and is in the process of
			 * releasing memory, we allow the "kill" to set
			 * TIF_MEMDIE, which will allow it to gain access to
			 * memory reserves.  Otherwise, it may stall forever.
			 *
			 * The loop isn't broken here, however, in case other
			 * threads are found to have already been oom killed.
			 */
			if (p == current) {
				chosen = p;
				*ppoints = 1000;
			} else if (!force_kill) {
				/*
				 * If this task is not being ptraced on exit,
				 * then wait for it to finish before killing
				 * some other task unnecessarily.
				 */
				if (!(p->group_leader->ptrace & PT_TRACE_EXIT))
					return ERR_PTR(-1UL);
			}
		}

		points = oom_badness(p, memcg, nodemask, totalpages);
		if (points > *ppoints) {
			chosen = p;
			*ppoints = points;
		}
	} while_each_thread(g, p);

/**
 * oom_badness - heuristic function to determine which candidate task to kill
 * @p: task struct of which task we should calculate
 * @totalpages: total present RAM allowed for page allocation
 *
 * The heuristic for determining which task to kill is made to be as simple and
 * predictable as possible.  The goal is to return the highest value for the
 * task consuming the most memory to avoid subsequent oom failures.
 */
unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
		      const nodemask_t *nodemask, unsigned long totalpages)
{
	int points;

	if (oom_unkillable_task(p, mem, nodemask))
		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	/*
	 * Shortcut check for a thread sharing p->mm that is OOM_SCORE_ADJ_MIN
	 * so the entire heuristic doesn't need to be executed for something
	 * that cannot be killed.
	 */
	if (atomic_read(&p->mm->oom_disable_count)) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The memory controller may have a limit of 0 bytes, so avoid a divide
	 * by zero, if necessary.
	 */
	if (!totalpages)
		totalpages = 1;

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
	points = get_mm_rss(p->mm) + p->mm->nr_ptes;
	points += get_mm_counter(p->mm, MM_SWAPENTS);

	points *= 1000;
	points /= totalpages;
	task_unlock(p);

	/*
	 * Root processes get 3% bonus, just like the __vm_enough_memory()
	 * implementation used by LSMs.
	 */
	if (has_capability_noaudit(p, CAP_SYS_ADMIN))
		points -= 30;

	/*
	 * /proc/pid/oom_score_adj ranges from -1000 to +1000 such that it may
	 * either completely disable oom killing or always prefer a certain
	 * task.
	 */
	points += p->signal->oom_score_adj;

	/*
	 * Never return 0 for an eligible task that may be killed since it's
	 * possible that no single user task uses more than 0.1% of memory and
	 * no single admin tasks uses more than 3.0%.
	 */
	if (points <= 0)
		return 1;
	return (points < 1000) ? points : 1000;
}

/*
 * If this is a system OOM (not a memcg OOM) and the task selected to be
 * killed is not already running at high (RT) priorities, speed up the
 * recovery by boosting the dying task to the lowest FIFO priority.
 * That helps with the recovery and avoids interfering with RT tasks.
 */
static void boost_dying_task_prio(struct task_struct *p,
				  struct mem_cgroup *mem)
{
	struct sched_param param = { .sched_priority = 1 };

	if (mem)
		return;

	if (!rt_task(p))
		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
}

/*
 * The process p may have detached its own ->mm while exiting or through
 * use_mm(), but one or more of its subthreads may still have a valid
 * pointer.  Return p, or any of its subthreads with a valid ->mm, with
 * task_lock() held.
 */
struct task_struct *find_lock_task_mm(struct task_struct *p)
{
	struct task_struct *t = p;

	do {
		task_lock(t);
		if (likely(t->mm))
			return t;
		task_unlock(t);
	} while_each_thread(p, t);

	return NULL;
}

/* return true if the task is not adequate as candidate victim task. */
static bool oom_unkillable_task(struct task_struct *p,
		const struct mem_cgroup *mem, const nodemask_t *nodemask)
{
	if (is_global_init(p))
		return true;
	if (p->flags & PF_KTHREAD)
		return true;

	/* When mem_cgroup_out_of_memory() and p is not member of the group */
	if (mem && !task_in_mem_cgroup(p, mem))
		return true;

	/* p may not have freeable memory in nodemask */
	if (!has_intersects_mems_allowed(p, nodemask))
		return true;

	return false;
}

/**
 * oom_badness - heuristic function to determine which candidate task to kill
 * @p: task struct of which task we should calculate
 * @totalpages: total present RAM allowed for page allocation
 *
 * The heuristic for determining which task to kill is made to be as simple and
 * predictable as possible.  The goal is to return the highest value for the
 * task consuming the most memory to avoid subsequent oom failures.
 */
unsigned int oom_badness(struct task_struct *p, struct mem_cgroup *mem,
		      const nodemask_t *nodemask, unsigned long totalpages)
{
	long points;

	if (oom_unkillable_task(p, mem, nodemask))
		return 0;

	p = find_lock_task_mm(p);
	if (!p)
		return 0;

	/*
	 * Shortcut check for a thread sharing p->mm that is OOM_SCORE_ADJ_MIN
	 * so the entire heuristic doesn't need to be executed for something
	 * that cannot be killed.
	 */
	if (atomic_read(&p->mm->oom_disable_count)) {
		task_unlock(p);
		return 0;
	}

	/*
	 * The memory controller may have a limit of 0 bytes, so avoid a divide
	 * by zero, if necessary.
	 */
	if (!totalpages)
		totalpages = 1;

	/*
	 * The baseline for the badness score is the proportion of RAM that each
	 * task's rss, pagetable and swap space use.
	 */
//.........这里部分代码省略.........

/**
 * out_of_memory - kill the "best" process when we run out of memory
 * @oc: pointer to struct oom_control
 *
 * 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.
 */
bool out_of_memory(struct oom_control *oc)
{
	unsigned long freed = 0;
	enum oom_constraint constraint = CONSTRAINT_NONE;

	if (oom_killer_disabled)
		return false;

	if (!is_memcg_oom(oc)) {
		blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
		if (freed > 0)
			/* Got some memory back in the last second. */
			return true;
	}

	/*
	 * If current has a pending SIGKILL or is exiting, then automatically
	 * select it.  The goal is to allow it to allocate so that it may
	 * quickly exit and free its memory.
	 */
	if (task_will_free_mem(current)) {
		mark_oom_victim(current);
		wake_oom_reaper(current);
		return true;
	}

	/*
	 * The OOM killer does not compensate for IO-less reclaim.
	 * pagefault_out_of_memory lost its gfp context so we have to
	 * make sure exclude 0 mask - all other users should have at least
	 * ___GFP_DIRECT_RECLAIM to get here.
	 */
	if (oc->gfp_mask && !(oc->gfp_mask & __GFP_FS))
		return true;

	/*
	 * Check if there were limitations on the allocation (only relevant for
	 * NUMA and memcg) that may require different handling.
	 */
	constraint = constrained_alloc(oc);
	if (constraint != CONSTRAINT_MEMORY_POLICY)
		oc->nodemask = NULL;
	check_panic_on_oom(oc, constraint);

	if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
	    current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
	    current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
		get_task_struct(current);
		oc->chosen = current;
		oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
		return true;
	}

	select_bad_process(oc);
	/* Found nothing?!?! */
	if (!oc->chosen) {
		dump_header(oc, NULL);
		pr_warn("Out of memory and no killable processes...\n");
		/*
		 * If we got here due to an actual allocation at the
		 * system level, we cannot survive this and will enter
		 * an endless loop in the allocator. Bail out now.
		 */
		if (!is_sysrq_oom(oc) && !is_memcg_oom(oc))
			panic("System is deadlocked on memory\n");
	}
	if (oc->chosen && oc->chosen != (void *)-1UL)
		oom_kill_process(oc, !is_memcg_oom(oc) ? "Out of memory" :
				 "Memory cgroup out of memory");
	return !!oc->chosen;
}