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.
18 #include <linux/oom.h>
20 #include <linux/err.h>
21 #include <linux/sched.h>
22 #include <linux/swap.h>
23 #include <linux/timex.h>
24 #include <linux/jiffies.h>
25 #include <linux/cpuset.h>
26 #include <linux/module.h>
27 #include <linux/notifier.h>
28 #include <linux/memcontrol.h>
30 int sysctl_panic_on_oom;
31 int sysctl_oom_kill_allocating_task;
32 static DEFINE_SPINLOCK(zone_scan_mutex);
36 * badness - calculate a numeric value for how bad this task has been
37 * @p: task struct of which task we should calculate
38 * @uptime: current uptime in seconds
40 * The formula used is relatively simple and documented inline in the
41 * function. The main rationale is that we want to select a good task
42 * to kill when we run out of memory.
44 * Good in this context means that:
45 * 1) we lose the minimum amount of work done
46 * 2) we recover a large amount of memory
47 * 3) we don't kill anything innocent of eating tons of memory
48 * 4) we want to kill the minimum amount of processes (one)
49 * 5) we try to kill the process the user expects us to kill, this
50 * algorithm has been meticulously tuned to meet the principle
51 * of least surprise ... (be careful when you change it)
54 unsigned long badness(struct task_struct *p, unsigned long uptime,
55 struct mem_cgroup *mem)
57 unsigned long points, cpu_time, run_time, s;
59 struct task_struct *child;
68 #ifdef CONFIG_CGROUP_MEM_CONT
69 if (mem != NULL && mm->mem_cgroup != mem) {
76 * The memory size of the process is the basis for the badness.
78 points = mm->total_vm;
81 * After this unlock we can no longer dereference local variable `mm'
86 * swapoff can easily use up all memory, so kill those first.
88 if (p->flags & PF_SWAPOFF)
92 * Processes which fork a lot of child processes are likely
93 * a good choice. We add half the vmsize of the children if they
94 * have an own mm. This prevents forking servers to flood the
95 * machine with an endless amount of children. In case a single
96 * child is eating the vast majority of memory, adding only half
97 * to the parents will make the child our kill candidate of choice.
99 list_for_each_entry(child, &p->children, sibling) {
101 if (child->mm != mm && child->mm)
102 points += child->mm->total_vm/2 + 1;
107 * CPU time is in tens of seconds and run time is in thousands
108 * of seconds. There is no particular reason for this other than
109 * that it turned out to work very well in practice.
111 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
114 if (uptime >= p->start_time.tv_sec)
115 run_time = (uptime - p->start_time.tv_sec) >> 10;
119 s = int_sqrt(cpu_time);
122 s = int_sqrt(int_sqrt(run_time));
127 * Niced processes are most likely less important, so double
128 * their badness points.
130 if (task_nice(p) > 0)
134 * Superuser processes are usually more important, so we make it
135 * less likely that we kill those.
137 if (__capable(p, CAP_SYS_ADMIN) || __capable(p, CAP_SYS_RESOURCE))
141 * We don't want to kill a process with direct hardware access.
142 * Not only could that mess up the hardware, but usually users
143 * tend to only have this flag set on applications they think
146 if (__capable(p, CAP_SYS_RAWIO))
150 * If p's nodes don't overlap ours, it may still help to kill p
151 * because p may have allocated or otherwise mapped memory on
152 * this node before. However it will be less likely.
154 if (!cpuset_mems_allowed_intersects(current, p))
158 * Adjust the score by oomkilladj.
161 if (p->oomkilladj > 0) {
164 points <<= p->oomkilladj;
166 points >>= -(p->oomkilladj);
170 printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n",
171 p->pid, p->comm, points);
177 * Determine the type of allocation constraint.
179 static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist,
184 nodemask_t nodes = node_states[N_HIGH_MEMORY];
186 for (z = zonelist->zones; *z; z++)
187 if (cpuset_zone_allowed_softwall(*z, gfp_mask))
188 node_clear(zone_to_nid(*z), nodes);
190 return CONSTRAINT_CPUSET;
192 if (!nodes_empty(nodes))
193 return CONSTRAINT_MEMORY_POLICY;
196 return CONSTRAINT_NONE;
200 * Simple selection loop. We chose the process with the highest
201 * number of 'points'. We expect the caller will lock the tasklist.
203 * (not docbooked, we don't want this one cluttering up the manual)
205 static struct task_struct *select_bad_process(unsigned long *ppoints,
206 struct mem_cgroup *mem)
208 struct task_struct *g, *p;
209 struct task_struct *chosen = NULL;
210 struct timespec uptime;
213 do_posix_clock_monotonic_gettime(&uptime);
214 do_each_thread(g, p) {
215 unsigned long points;
218 * skip kernel threads and tasks which have already released
223 /* skip the init task */
224 if (is_global_init(p))
228 * This task already has access to memory reserves and is
229 * being killed. Don't allow any other task access to the
232 * Note: this may have a chance of deadlock if it gets
233 * blocked waiting for another task which itself is waiting
234 * for memory. Is there a better alternative?
236 if (test_tsk_thread_flag(p, TIF_MEMDIE))
237 return ERR_PTR(-1UL);
240 * This is in the process of releasing memory so wait for it
241 * to finish before killing some other task by mistake.
243 * However, if p is the current task, we allow the 'kill' to
244 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
245 * which will allow it to gain access to memory reserves in
246 * the process of exiting and releasing its resources.
247 * Otherwise we could get an easy OOM deadlock.
249 if (p->flags & PF_EXITING) {
251 return ERR_PTR(-1UL);
254 *ppoints = ULONG_MAX;
257 if (p->oomkilladj == OOM_DISABLE)
260 points = badness(p, uptime.tv_sec, mem);
261 if (points > *ppoints || !chosen) {
265 } while_each_thread(g, p);
271 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
272 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
275 static void __oom_kill_task(struct task_struct *p, int verbose)
277 if (is_global_init(p)) {
279 printk(KERN_WARNING "tried to kill init!\n");
285 printk(KERN_WARNING "tried to kill an mm-less task!\n");
290 printk(KERN_ERR "Killed process %d (%s)\n",
291 task_pid_nr(p), p->comm);
294 * We give our sacrificial lamb high priority and access to
295 * all the memory it needs. That way it should be able to
296 * exit() and clear out its resources quickly...
298 p->rt.time_slice = HZ;
299 set_tsk_thread_flag(p, TIF_MEMDIE);
301 force_sig(SIGKILL, p);
304 static int oom_kill_task(struct task_struct *p)
306 struct mm_struct *mm;
307 struct task_struct *g, *q;
311 /* WARNING: mm may not be dereferenced since we did not obtain its
312 * value from get_task_mm(p). This is OK since all we need to do is
313 * compare mm to q->mm below.
315 * Furthermore, even if mm contains a non-NULL value, p->mm may
316 * change to NULL at any time since we do not hold task_lock(p).
317 * However, this is of no concern to us.
324 * Don't kill the process if any threads are set to OOM_DISABLE
326 do_each_thread(g, q) {
327 if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
329 } while_each_thread(g, q);
331 __oom_kill_task(p, 1);
334 * kill all processes that share the ->mm (i.e. all threads),
335 * but are in a different thread group. Don't let them have access
336 * to memory reserves though, otherwise we might deplete all memory.
338 do_each_thread(g, q) {
339 if (q->mm == mm && !same_thread_group(q, p))
340 force_sig(SIGKILL, q);
341 } while_each_thread(g, q);
346 static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
347 unsigned long points, const char *message)
349 struct task_struct *c;
351 if (printk_ratelimit()) {
352 printk(KERN_WARNING "%s invoked oom-killer: "
353 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
354 current->comm, gfp_mask, order, current->oomkilladj);
360 * If the task is already exiting, don't alarm the sysadmin or kill
361 * its children or threads, just set TIF_MEMDIE so it can die quickly
363 if (p->flags & PF_EXITING) {
364 __oom_kill_task(p, 0);
368 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
369 message, task_pid_nr(p), p->comm, points);
371 /* Try to kill a child first */
372 list_for_each_entry(c, &p->children, sibling) {
375 if (!oom_kill_task(c))
378 return oom_kill_task(p);
381 #ifdef CONFIG_CGROUP_MEM_CONT
382 void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
384 unsigned long points = 0;
385 struct task_struct *p;
390 p = select_bad_process(&points, mem);
391 if (PTR_ERR(p) == -1UL)
397 if (oom_kill_process(p, gfp_mask, 0, points,
398 "Memory cgroup out of memory"))
406 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
408 int register_oom_notifier(struct notifier_block *nb)
410 return blocking_notifier_chain_register(&oom_notify_list, nb);
412 EXPORT_SYMBOL_GPL(register_oom_notifier);
414 int unregister_oom_notifier(struct notifier_block *nb)
416 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
418 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
421 * Try to acquire the OOM killer lock for the zones in zonelist. Returns zero
422 * if a parallel OOM killing is already taking place that includes a zone in
423 * the zonelist. Otherwise, locks all zones in the zonelist and returns 1.
425 int try_set_zone_oom(struct zonelist *zonelist)
432 spin_lock(&zone_scan_mutex);
434 if (zone_is_oom_locked(*z)) {
438 } while (*(++z) != NULL);
441 * Lock each zone in the zonelist under zone_scan_mutex so a parallel
442 * invocation of try_set_zone_oom() doesn't succeed when it shouldn't.
446 zone_set_flag(*z, ZONE_OOM_LOCKED);
447 } while (*(++z) != NULL);
449 spin_unlock(&zone_scan_mutex);
454 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
455 * allocation attempts with zonelists containing them may now recall the OOM
456 * killer, if necessary.
458 void clear_zonelist_oom(struct zonelist *zonelist)
464 spin_lock(&zone_scan_mutex);
466 zone_clear_flag(*z, ZONE_OOM_LOCKED);
467 } while (*(++z) != NULL);
468 spin_unlock(&zone_scan_mutex);
472 * out_of_memory - kill the "best" process when we run out of memory
474 * If we run out of memory, we have the choice between either
475 * killing a random task (bad), letting the system crash (worse)
476 * OR try to be smart about which process to kill. Note that we
477 * don't have to be perfect here, we just have to be good.
479 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
481 struct task_struct *p;
482 unsigned long points = 0;
483 unsigned long freed = 0;
484 enum oom_constraint constraint;
486 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
488 /* Got some memory back in the last second. */
491 if (sysctl_panic_on_oom == 2)
492 panic("out of memory. Compulsory panic_on_oom is selected.\n");
495 * Check if there were limitations on the allocation (only relevant for
496 * NUMA) that may require different handling.
498 constraint = constrained_alloc(zonelist, gfp_mask);
499 read_lock(&tasklist_lock);
501 switch (constraint) {
502 case CONSTRAINT_MEMORY_POLICY:
503 oom_kill_process(current, gfp_mask, order, points,
504 "No available memory (MPOL_BIND)");
507 case CONSTRAINT_NONE:
508 if (sysctl_panic_on_oom)
509 panic("out of memory. panic_on_oom is selected\n");
511 case CONSTRAINT_CPUSET:
512 if (sysctl_oom_kill_allocating_task) {
513 oom_kill_process(current, gfp_mask, order, points,
514 "Out of memory (oom_kill_allocating_task)");
519 * Rambo mode: Shoot down a process and hope it solves whatever
520 * issues we may have.
522 p = select_bad_process(&points, NULL);
524 if (PTR_ERR(p) == -1UL)
527 /* Found nothing?!?! Either we hang forever, or we panic. */
529 read_unlock(&tasklist_lock);
530 panic("Out of memory and no killable processes...\n");
533 if (oom_kill_process(p, gfp_mask, order, points,
541 read_unlock(&tasklist_lock);
544 * Give "p" a good chance of killing itself before we
545 * retry to allocate memory unless "p" is current
547 if (!test_thread_flag(TIF_MEMDIE))
548 schedule_timeout_uninterruptible(1);