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>
23 #include <linux/cpuset.h>
24 #include <linux/module.h>
25 #include <linux/notifier.h>
27 int sysctl_panic_on_oom;
31 * badness - calculate a numeric value for how bad this task has been
32 * @p: task struct of which task we should calculate
33 * @uptime: current uptime in seconds
35 * The formula used is relatively simple and documented inline in the
36 * function. The main rationale is that we want to select a good task
37 * to kill when we run out of memory.
39 * Good in this context means that:
40 * 1) we lose the minimum amount of work done
41 * 2) we recover a large amount of memory
42 * 3) we don't kill anything innocent of eating tons of memory
43 * 4) we want to kill the minimum amount of processes (one)
44 * 5) we try to kill the process the user expects us to kill, this
45 * algorithm has been meticulously tuned to meet the principle
46 * of least surprise ... (be careful when you change it)
49 unsigned long badness(struct task_struct *p, unsigned long uptime)
51 unsigned long points, cpu_time, run_time, s;
53 struct task_struct *child;
63 * The memory size of the process is the basis for the badness.
65 points = mm->total_vm;
68 * After this unlock we can no longer dereference local variable `mm'
73 * Processes which fork a lot of child processes are likely
74 * a good choice. We add half the vmsize of the children if they
75 * have an own mm. This prevents forking servers to flood the
76 * machine with an endless amount of children. In case a single
77 * child is eating the vast majority of memory, adding only half
78 * to the parents will make the child our kill candidate of choice.
80 list_for_each_entry(child, &p->children, sibling) {
82 if (child->mm != mm && child->mm)
83 points += child->mm->total_vm/2 + 1;
88 * CPU time is in tens of seconds and run time is in thousands
89 * of seconds. There is no particular reason for this other than
90 * that it turned out to work very well in practice.
92 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
95 if (uptime >= p->start_time.tv_sec)
96 run_time = (uptime - p->start_time.tv_sec) >> 10;
100 s = int_sqrt(cpu_time);
103 s = int_sqrt(int_sqrt(run_time));
108 * Niced processes are most likely less important, so double
109 * their badness points.
111 if (task_nice(p) > 0)
115 * Superuser processes are usually more important, so we make it
116 * less likely that we kill those.
118 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
119 p->uid == 0 || p->euid == 0)
123 * We don't want to kill a process with direct hardware access.
124 * Not only could that mess up the hardware, but usually users
125 * tend to only have this flag set on applications they think
128 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
132 * If p's nodes don't overlap ours, it may still help to kill p
133 * because p may have allocated or otherwise mapped memory on
134 * this node before. However it will be less likely.
136 if (!cpuset_excl_nodes_overlap(p))
140 * Adjust the score by oomkilladj.
143 if (p->oomkilladj > 0)
144 points <<= p->oomkilladj;
146 points >>= -(p->oomkilladj);
150 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
151 p->pid, p->comm, points);
157 * Types of limitations to the nodes from which allocations may occur
159 #define CONSTRAINT_NONE 1
160 #define CONSTRAINT_MEMORY_POLICY 2
161 #define CONSTRAINT_CPUSET 3
164 * Determine the type of allocation constraint.
166 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
170 nodemask_t nodes = node_online_map;
172 for (z = zonelist->zones; *z; z++)
173 if (cpuset_zone_allowed(*z, gfp_mask))
174 node_clear((*z)->zone_pgdat->node_id,
177 return CONSTRAINT_CPUSET;
179 if (!nodes_empty(nodes))
180 return CONSTRAINT_MEMORY_POLICY;
183 return CONSTRAINT_NONE;
187 * Simple selection loop. We chose the process with the highest
188 * number of 'points'. We expect the caller will lock the tasklist.
190 * (not docbooked, we don't want this one cluttering up the manual)
192 static struct task_struct *select_bad_process(unsigned long *ppoints)
194 struct task_struct *g, *p;
195 struct task_struct *chosen = NULL;
196 struct timespec uptime;
199 do_posix_clock_monotonic_gettime(&uptime);
200 do_each_thread(g, p) {
201 unsigned long points;
204 /* skip the init task with pid == 1 */
209 * This is in the process of releasing memory so wait for it
210 * to finish before killing some other task by mistake.
212 * However, if p is the current task, we allow the 'kill' to
213 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
214 * which will allow it to gain access to memory reserves in
215 * the process of exiting and releasing its resources.
216 * Otherwise we could get an OOM deadlock.
218 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
219 p->flags & PF_EXITING;
221 /* PF_DEAD tasks have already released their mm */
222 if (p->flags & PF_DEAD)
224 if (p->flags & PF_EXITING && p == current) {
226 *ppoints = ULONG_MAX;
229 return ERR_PTR(-1UL);
231 if (p->oomkilladj == OOM_DISABLE)
233 if (p->flags & PF_SWAPOFF)
236 points = badness(p, uptime.tv_sec);
237 if (points > *ppoints || !chosen) {
241 } while_each_thread(g, p);
246 * We must be careful though to never send SIGKILL a process with
247 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
248 * we select a process with CAP_SYS_RAW_IO set).
250 static void __oom_kill_task(struct task_struct *p, const char *message)
254 printk(KERN_WARNING "tried to kill init!\n");
259 if (!p->mm || p->mm == &init_mm) {
261 printk(KERN_WARNING "tried to kill an mm-less task!\n");
268 printk(KERN_ERR "%s: Killed process %d (%s).\n",
269 message, p->pid, p->comm);
273 * We give our sacrificial lamb high priority and access to
274 * all the memory it needs. That way it should be able to
275 * exit() and clear out its resources quickly...
278 set_tsk_thread_flag(p, TIF_MEMDIE);
280 force_sig(SIGKILL, p);
283 static int oom_kill_task(struct task_struct *p, const char *message)
285 struct mm_struct *mm;
286 struct task_struct *g, *q;
290 /* WARNING: mm may not be dereferenced since we did not obtain its
291 * value from get_task_mm(p). This is OK since all we need to do is
292 * compare mm to q->mm below.
294 * Furthermore, even if mm contains a non-NULL value, p->mm may
295 * change to NULL at any time since we do not hold task_lock(p).
296 * However, this is of no concern to us.
299 if (mm == NULL || mm == &init_mm)
302 __oom_kill_task(p, message);
304 * kill all processes that share the ->mm (i.e. all threads),
305 * but are in a different thread group
308 if (q->mm == mm && q->tgid != p->tgid)
309 __oom_kill_task(q, message);
310 while_each_thread(g, q);
315 static int oom_kill_process(struct task_struct *p, unsigned long points,
318 struct task_struct *c;
319 struct list_head *tsk;
322 * If the task is already exiting, don't alarm the sysadmin or kill
323 * its children or threads, just set TIF_MEMDIE so it can die quickly
325 if (p->flags & PF_EXITING) {
326 __oom_kill_task(p, NULL);
330 printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li"
331 " and children.\n", p->pid, p->comm, points);
332 /* Try to kill a child first */
333 list_for_each(tsk, &p->children) {
334 c = list_entry(tsk, struct task_struct, sibling);
337 if (!oom_kill_task(c, message))
340 return oom_kill_task(p, message);
343 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
345 int register_oom_notifier(struct notifier_block *nb)
347 return blocking_notifier_chain_register(&oom_notify_list, nb);
349 EXPORT_SYMBOL_GPL(register_oom_notifier);
351 int unregister_oom_notifier(struct notifier_block *nb)
353 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
355 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
358 * out_of_memory - kill the "best" process when we run out of memory
360 * If we run out of memory, we have the choice between either
361 * killing a random task (bad), letting the system crash (worse)
362 * OR try to be smart about which process to kill. Note that we
363 * don't have to be perfect here, we just have to be good.
365 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
367 struct task_struct *p;
368 unsigned long points = 0;
369 unsigned long freed = 0;
371 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
373 /* Got some memory back in the last second. */
376 if (printk_ratelimit()) {
377 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
384 read_lock(&tasklist_lock);
387 * Check if there were limitations on the allocation (only relevant for
388 * NUMA) that may require different handling.
390 switch (constrained_alloc(zonelist, gfp_mask)) {
391 case CONSTRAINT_MEMORY_POLICY:
392 oom_kill_process(current, points,
393 "No available memory (MPOL_BIND)");
396 case CONSTRAINT_CPUSET:
397 oom_kill_process(current, points,
398 "No available memory in cpuset");
401 case CONSTRAINT_NONE:
402 if (sysctl_panic_on_oom)
403 panic("out of memory. panic_on_oom is selected\n");
406 * Rambo mode: Shoot down a process and hope it solves whatever
407 * issues we may have.
409 p = select_bad_process(&points);
411 if (PTR_ERR(p) == -1UL)
414 /* Found nothing?!?! Either we hang forever, or we panic. */
416 read_unlock(&tasklist_lock);
418 panic("Out of memory and no killable processes...\n");
421 if (oom_kill_process(p, points, "Out of memory"))
428 read_unlock(&tasklist_lock);
432 * Give "p" a good chance of killing itself before we
433 * retry to allocate memory unless "p" is current
435 if (!test_thread_flag(TIF_MEMDIE))
436 schedule_timeout_uninterruptible(1);