1 files changed, 292 insertions, 0 deletions
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
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+/*
+ *  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 kswapd()
+ *  in linux/mm/vmscan.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/mm.h>
+#include <linux/sched.h>
+#include <linux/swap.h>
+#include <linux/timex.h>
+#include <linux/jiffies.h>
+
+/* #define DEBUG */
+
+/**
+ * oom_badness - calculate a numeric value for how bad this task has been
+ * @p: task struct of which task we should calculate
+ * @p: 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 list_head *tsk;
+
+	if (!p->mm)
+		return 0;
+
+	/*
+	 * The memory size of the process is the basis for the badness.
+	 */
+	points = p->mm->total_vm;
+
+	/*
+	 * Processes which fork a lot of child processes are likely
+	 * a good choice. We add the vmsize of the childs if they
+	 * have an own mm. This prevents forking servers to flood the
+	 * machine with an endless amount of childs
+	 */
+	list_for_each(tsk, &p->children) {
+		struct task_struct *chld;
+		chld = list_entry(tsk, struct task_struct, sibling);
+		if (chld->mm != p->mm && chld->mm)
+			points += chld->mm->total_vm;
+	}
+
+	/*
+	 * 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;
+
+	/*
+	 * 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\n",
+	p->pid, p->comm, points);
+#endif
+	return points;
+}
+
+/*
+ * 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(void)
+{
+	unsigned long maxpoints = 0;
+	struct task_struct *g, *p;
+	struct task_struct *chosen = NULL;
+	struct timespec uptime;
+
+	do_posix_clock_monotonic_gettime(&uptime);
+	do_each_thread(g, p)
+		/* skip the init task with pid == 1 */
+		if (p->pid > 1) {
+			unsigned long points;
+
+			/*
+			 * This is in the process of releasing memory so wait it
+			 * to finish before killing some other task by mistake.
+			 */
+			if ((unlikely(test_tsk_thread_flag(p, TIF_MEMDIE)) || (p->flags & PF_EXITING)) &&
+			    !(p->flags & PF_DEAD))
+				return ERR_PTR(-1UL);
+			if (p->flags & PF_SWAPOFF)
+				return p;
+
+			points = badness(p, uptime.tv_sec);
+			if (points > maxpoints || !chosen) {
+				chosen = p;
+				maxpoints = points;
+			}
+		}
+	while_each_thread(g, p);
+	return chosen;
+}
+
+/**
+ * We must be careful though to never send SIGKILL a process with
+ * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
+ * we select a process with CAP_SYS_RAW_IO set).
+ */
+static void __oom_kill_task(task_t *p)
+{
+	if (p->pid == 1) {
+		WARN_ON(1);
+		printk(KERN_WARNING "tried to kill init!\n");
+		return;
+	}
+
+	task_lock(p);
+	if (!p->mm || p->mm == &init_mm) {
+		WARN_ON(1);
+		printk(KERN_WARNING "tried to kill an mm-less task!\n");
+		task_unlock(p);
+		return;
+	}
+	task_unlock(p);
+	printk(KERN_ERR "Out of Memory: 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 struct mm_struct *oom_kill_task(task_t *p)
+{
+	struct mm_struct *mm = get_task_mm(p);
+	task_t * g, * q;
+
+	if (!mm)
+		return NULL;
+	if (mm == &init_mm) {
+		mmput(mm);
+		return NULL;
+	}
+
+	__oom_kill_task(p);
+	/*
+	 * 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);
+	while_each_thread(g, q);
+
+	return mm;
+}
+
+static struct mm_struct *oom_kill_process(struct task_struct *p)
+{
+ 	struct mm_struct *mm;
+	struct task_struct *c;
+	struct list_head *tsk;
+
+	/* 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;
+		mm = oom_kill_task(c);
+		if (mm)
+			return mm;
+	}
+	return oom_kill_task(p);
+}
+
+/**
+ * oom_kill - 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(unsigned int __nocast gfp_mask)
+{
+	struct mm_struct *mm = NULL;
+	task_t * p;
+
+	read_lock(&tasklist_lock);
+retry:
+	p = select_bad_process();
+
+	if (PTR_ERR(p) == -1UL)
+		goto out;
+
+	/* Found nothing?!?! Either we hang forever, or we panic. */
+	if (!p) {
+		read_unlock(&tasklist_lock);
+		show_free_areas();
+		panic("Out of memory and no killable processes...\n");
+	}
+
+	printk("oom-killer: gfp_mask=0x%x\n", gfp_mask);
+	show_free_areas();
+	mm = oom_kill_process(p);
+	if (!mm)
+		goto retry;
+
+ out:
+	read_unlock(&tasklist_lock);
+	if (mm)
+		mmput(mm);
+
+	/*
+	 * Give "p" a good chance of killing itself before we
+	 * retry to allocate memory.
+	 */
+	__set_current_state(TASK_INTERRUPTIBLE);
+	schedule_timeout(1);
+}