4 * Copyright (C) 1998,2000 Rik van Riel
5 * Thanks go out to Claus Fischer for some serious inspiration and
6 * for goading me into coding this file...
8 * The routines in this file are used to kill a process when
9 * we're seriously out of memory. This gets called from __alloc_pages()
10 * in mm/page_alloc.c when we really run out of memory.
12 * Since we won't call these routines often (on a well-configured
13 * machine) this file will double as a 'coding guide' and a signpost
14 * for newbie kernel hackers. It features several pointers to major
15 * kernel subsystems and hints as to where to find out what things do.
19 #include <linux/sched.h>
20 #include <linux/swap.h>
21 #include <linux/timex.h>
22 #include <linux/jiffies.h>
27 * oom_badness - calculate a numeric value for how bad this task has been
28 * @p: task struct of which task we should calculate
29 * @uptime: current uptime in seconds
31 * The formula used is relatively simple and documented inline in the
32 * function. The main rationale is that we want to select a good task
33 * to kill when we run out of memory.
35 * Good in this context means that:
36 * 1) we lose the minimum amount of work done
37 * 2) we recover a large amount of memory
38 * 3) we don't kill anything innocent of eating tons of memory
39 * 4) we want to kill the minimum amount of processes (one)
40 * 5) we try to kill the process the user expects us to kill, this
41 * algorithm has been meticulously tuned to meet the principle
42 * of least surprise ... (be careful when you change it)
45 unsigned long badness(struct task_struct *p, unsigned long uptime)
47 unsigned long points, cpu_time, run_time, s;
48 struct list_head *tsk;
54 * The memory size of the process is the basis for the badness.
56 points = p->mm->total_vm;
59 * Processes which fork a lot of child processes are likely
60 * a good choice. We add the vmsize of the children if they
61 * have an own mm. This prevents forking servers to flood the
62 * machine with an endless amount of children
64 list_for_each(tsk, &p->children) {
65 struct task_struct *chld;
66 chld = list_entry(tsk, struct task_struct, sibling);
67 if (chld->mm != p->mm && chld->mm)
68 points += chld->mm->total_vm;
72 * CPU time is in tens of seconds and run time is in thousands
73 * of seconds. There is no particular reason for this other than
74 * that it turned out to work very well in practice.
76 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
79 if (uptime >= p->start_time.tv_sec)
80 run_time = (uptime - p->start_time.tv_sec) >> 10;
84 s = int_sqrt(cpu_time);
87 s = int_sqrt(int_sqrt(run_time));
92 * Niced processes are most likely less important, so double
93 * their badness points.
99 * Superuser processes are usually more important, so we make it
100 * less likely that we kill those.
102 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
103 p->uid == 0 || p->euid == 0)
107 * We don't want to kill a process with direct hardware access.
108 * Not only could that mess up the hardware, but usually users
109 * tend to only have this flag set on applications they think
112 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
116 * Adjust the score by oomkilladj.
119 if (p->oomkilladj > 0)
120 points <<= p->oomkilladj;
122 points >>= -(p->oomkilladj);
126 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
127 p->pid, p->comm, points);
133 * Simple selection loop. We chose the process with the highest
134 * number of 'points'. We expect the caller will lock the tasklist.
136 * (not docbooked, we don't want this one cluttering up the manual)
138 static struct task_struct * select_bad_process(void)
140 unsigned long maxpoints = 0;
141 struct task_struct *g, *p;
142 struct task_struct *chosen = NULL;
143 struct timespec uptime;
145 do_posix_clock_monotonic_gettime(&uptime);
146 do_each_thread(g, p) {
147 unsigned long points;
150 /* skip the init task with pid == 1 */
153 if (p->oomkilladj == OOM_DISABLE)
156 * This is in the process of releasing memory so for wait it
157 * to finish before killing some other task by mistake.
159 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
160 p->flags & PF_EXITING;
161 if (releasing && !(p->flags & PF_DEAD))
162 return ERR_PTR(-1UL);
163 if (p->flags & PF_SWAPOFF)
166 points = badness(p, uptime.tv_sec);
167 if (points > maxpoints || !chosen) {
171 } while_each_thread(g, p);
176 * We must be careful though to never send SIGKILL a process with
177 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
178 * we select a process with CAP_SYS_RAW_IO set).
180 static void __oom_kill_task(task_t *p)
184 printk(KERN_WARNING "tried to kill init!\n");
189 if (!p->mm || p->mm == &init_mm) {
191 printk(KERN_WARNING "tried to kill an mm-less task!\n");
196 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n",
200 * We give our sacrificial lamb high priority and access to
201 * all the memory it needs. That way it should be able to
202 * exit() and clear out its resources quickly...
205 set_tsk_thread_flag(p, TIF_MEMDIE);
207 force_sig(SIGKILL, p);
210 static struct mm_struct *oom_kill_task(task_t *p)
212 struct mm_struct *mm = get_task_mm(p);
217 if (mm == &init_mm) {
224 * kill all processes that share the ->mm (i.e. all threads),
225 * but are in a different thread group
228 if (q->mm == mm && q->tgid != p->tgid)
230 while_each_thread(g, q);
235 static struct mm_struct *oom_kill_process(struct task_struct *p)
237 struct mm_struct *mm;
238 struct task_struct *c;
239 struct list_head *tsk;
241 /* Try to kill a child first */
242 list_for_each(tsk, &p->children) {
243 c = list_entry(tsk, struct task_struct, sibling);
246 mm = oom_kill_task(c);
250 return oom_kill_task(p);
254 * oom_kill - kill the "best" process when we run out of memory
256 * If we run out of memory, we have the choice between either
257 * killing a random task (bad), letting the system crash (worse)
258 * OR try to be smart about which process to kill. Note that we
259 * don't have to be perfect here, we just have to be good.
261 void out_of_memory(unsigned int __nocast gfp_mask, int order)
263 struct mm_struct *mm = NULL;
266 if (printk_ratelimit()) {
267 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
272 read_lock(&tasklist_lock);
274 p = select_bad_process();
276 if (PTR_ERR(p) == -1UL)
279 /* Found nothing?!?! Either we hang forever, or we panic. */
281 read_unlock(&tasklist_lock);
282 panic("Out of memory and no killable processes...\n");
285 mm = oom_kill_process(p);
290 read_unlock(&tasklist_lock);
295 * Give "p" a good chance of killing itself before we
296 * retry to allocate memory.
298 __set_current_state(TASK_INTERRUPTIBLE);