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>
29 int sysctl_panic_on_oom;
33 * badness - calculate a numeric value for how bad this task has been
34 * @p: task struct of which task we should calculate
35 * @uptime: current uptime in seconds
37 * The formula used is relatively simple and documented inline in the
38 * function. The main rationale is that we want to select a good task
39 * to kill when we run out of memory.
41 * Good in this context means that:
42 * 1) we lose the minimum amount of work done
43 * 2) we recover a large amount of memory
44 * 3) we don't kill anything innocent of eating tons of memory
45 * 4) we want to kill the minimum amount of processes (one)
46 * 5) we try to kill the process the user expects us to kill, this
47 * algorithm has been meticulously tuned to meet the principle
48 * of least surprise ... (be careful when you change it)
51 unsigned long badness(struct task_struct *p, unsigned long uptime)
53 unsigned long points, cpu_time, run_time, s;
55 struct task_struct *child;
65 * The memory size of the process is the basis for the badness.
67 points = mm->total_vm;
70 * After this unlock we can no longer dereference local variable `mm'
75 * swapoff can easily use up all memory, so kill those first.
77 if (p->flags & PF_SWAPOFF)
81 * Processes which fork a lot of child processes are likely
82 * a good choice. We add half the vmsize of the children if they
83 * have an own mm. This prevents forking servers to flood the
84 * machine with an endless amount of children. In case a single
85 * child is eating the vast majority of memory, adding only half
86 * to the parents will make the child our kill candidate of choice.
88 list_for_each_entry(child, &p->children, sibling) {
90 if (child->mm != mm && child->mm)
91 points += child->mm->total_vm/2 + 1;
96 * CPU time is in tens of seconds and run time is in thousands
97 * of seconds. There is no particular reason for this other than
98 * that it turned out to work very well in practice.
100 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
103 if (uptime >= p->start_time.tv_sec)
104 run_time = (uptime - p->start_time.tv_sec) >> 10;
108 s = int_sqrt(cpu_time);
111 s = int_sqrt(int_sqrt(run_time));
116 * Niced processes are most likely less important, so double
117 * their badness points.
119 if (task_nice(p) > 0)
123 * Superuser processes are usually more important, so we make it
124 * less likely that we kill those.
126 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
127 p->uid == 0 || p->euid == 0)
131 * We don't want to kill a process with direct hardware access.
132 * Not only could that mess up the hardware, but usually users
133 * tend to only have this flag set on applications they think
136 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
140 * If p's nodes don't overlap ours, it may still help to kill p
141 * because p may have allocated or otherwise mapped memory on
142 * this node before. However it will be less likely.
144 if (!cpuset_excl_nodes_overlap(p))
148 * Adjust the score by oomkilladj.
151 if (p->oomkilladj > 0) {
154 points <<= p->oomkilladj;
156 points >>= -(p->oomkilladj);
160 printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n",
161 p->pid, p->comm, points);
167 * Types of limitations to the nodes from which allocations may occur
169 #define CONSTRAINT_NONE 1
170 #define CONSTRAINT_MEMORY_POLICY 2
171 #define CONSTRAINT_CPUSET 3
174 * Determine the type of allocation constraint.
176 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
184 /* node has memory ? */
185 for_each_online_node(node)
186 if (NODE_DATA(node)->node_present_pages)
187 node_set(node, nodes);
189 for (z = zonelist->zones; *z; z++)
190 if (cpuset_zone_allowed_softwall(*z, gfp_mask))
191 node_clear(zone_to_nid(*z), nodes);
193 return CONSTRAINT_CPUSET;
195 if (!nodes_empty(nodes))
196 return CONSTRAINT_MEMORY_POLICY;
199 return CONSTRAINT_NONE;
203 * Simple selection loop. We chose the process with the highest
204 * number of 'points'. We expect the caller will lock the tasklist.
206 * (not docbooked, we don't want this one cluttering up the manual)
208 static struct task_struct *select_bad_process(unsigned long *ppoints)
210 struct task_struct *g, *p;
211 struct task_struct *chosen = NULL;
212 struct timespec uptime;
215 do_posix_clock_monotonic_gettime(&uptime);
216 do_each_thread(g, p) {
217 unsigned long points;
220 * skip kernel threads and tasks which have already released
225 /* skip the init task */
230 * This task already has access to memory reserves and is
231 * being killed. Don't allow any other task access to the
234 * Note: this may have a chance of deadlock if it gets
235 * blocked waiting for another task which itself is waiting
236 * for memory. Is there a better alternative?
238 if (test_tsk_thread_flag(p, TIF_MEMDIE))
239 return ERR_PTR(-1UL);
242 * This is in the process of releasing memory so wait for it
243 * to finish before killing some other task by mistake.
245 * However, if p is the current task, we allow the 'kill' to
246 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
247 * which will allow it to gain access to memory reserves in
248 * the process of exiting and releasing its resources.
249 * Otherwise we could get an easy OOM deadlock.
251 if (p->flags & PF_EXITING) {
253 return ERR_PTR(-1UL);
256 *ppoints = ULONG_MAX;
259 if (p->oomkilladj == OOM_DISABLE)
262 points = badness(p, uptime.tv_sec);
263 if (points > *ppoints || !chosen) {
267 } while_each_thread(g, p);
273 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
274 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
277 static void __oom_kill_task(struct task_struct *p, int verbose)
281 printk(KERN_WARNING "tried to kill init!\n");
287 printk(KERN_WARNING "tried to kill an mm-less task!\n");
292 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm);
295 * We give our sacrificial lamb high priority and access to
296 * all the memory it needs. That way it should be able to
297 * exit() and clear out its resources quickly...
300 set_tsk_thread_flag(p, TIF_MEMDIE);
302 force_sig(SIGKILL, p);
305 static int oom_kill_task(struct task_struct *p)
307 struct mm_struct *mm;
308 struct task_struct *g, *q;
312 /* WARNING: mm may not be dereferenced since we did not obtain its
313 * value from get_task_mm(p). This is OK since all we need to do is
314 * compare mm to q->mm below.
316 * Furthermore, even if mm contains a non-NULL value, p->mm may
317 * change to NULL at any time since we do not hold task_lock(p).
318 * However, this is of no concern to us.
325 * Don't kill the process if any threads are set to OOM_DISABLE
327 do_each_thread(g, q) {
328 if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
330 } while_each_thread(g, q);
332 __oom_kill_task(p, 1);
335 * kill all processes that share the ->mm (i.e. all threads),
336 * but are in a different thread group. Don't let them have access
337 * to memory reserves though, otherwise we might deplete all memory.
339 do_each_thread(g, q) {
340 if (q->mm == mm && q->tgid != p->tgid)
341 force_sig(SIGKILL, q);
342 } while_each_thread(g, q);
347 static int oom_kill_process(struct task_struct *p, unsigned long points,
350 struct task_struct *c;
351 struct list_head *tsk;
354 * If the task is already exiting, don't alarm the sysadmin or kill
355 * its children or threads, just set TIF_MEMDIE so it can die quickly
357 if (p->flags & PF_EXITING) {
358 __oom_kill_task(p, 0);
362 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
363 message, p->pid, p->comm, points);
365 /* Try to kill a child first */
366 list_for_each(tsk, &p->children) {
367 c = list_entry(tsk, struct task_struct, sibling);
370 if (!oom_kill_task(c))
373 return oom_kill_task(p);
376 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
378 int register_oom_notifier(struct notifier_block *nb)
380 return blocking_notifier_chain_register(&oom_notify_list, nb);
382 EXPORT_SYMBOL_GPL(register_oom_notifier);
384 int unregister_oom_notifier(struct notifier_block *nb)
386 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
388 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
391 * out_of_memory - kill the "best" process when we run out of memory
393 * If we run out of memory, we have the choice between either
394 * killing a random task (bad), letting the system crash (worse)
395 * OR try to be smart about which process to kill. Note that we
396 * don't have to be perfect here, we just have to be good.
398 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
400 struct task_struct *p;
401 unsigned long points = 0;
402 unsigned long freed = 0;
405 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
407 /* Got some memory back in the last second. */
410 if (printk_ratelimit()) {
411 printk(KERN_WARNING "%s invoked oom-killer: "
412 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
413 current->comm, gfp_mask, order, current->oomkilladj);
418 if (sysctl_panic_on_oom == 2)
419 panic("out of memory. Compulsory panic_on_oom is selected.\n");
422 * Check if there were limitations on the allocation (only relevant for
423 * NUMA) that may require different handling.
425 constraint = constrained_alloc(zonelist, gfp_mask);
427 read_lock(&tasklist_lock);
429 switch (constraint) {
430 case CONSTRAINT_MEMORY_POLICY:
431 oom_kill_process(current, points,
432 "No available memory (MPOL_BIND)");
435 case CONSTRAINT_CPUSET:
436 oom_kill_process(current, points,
437 "No available memory in cpuset");
440 case CONSTRAINT_NONE:
441 if (sysctl_panic_on_oom)
442 panic("out of memory. panic_on_oom is selected\n");
445 * Rambo mode: Shoot down a process and hope it solves whatever
446 * issues we may have.
448 p = select_bad_process(&points);
450 if (PTR_ERR(p) == -1UL)
453 /* Found nothing?!?! Either we hang forever, or we panic. */
455 read_unlock(&tasklist_lock);
457 panic("Out of memory and no killable processes...\n");
460 if (oom_kill_process(p, points, "Out of memory"))
467 read_unlock(&tasklist_lock);
471 * Give "p" a good chance of killing itself before we
472 * retry to allocate memory unless "p" is current
474 if (!test_thread_flag(TIF_MEMDIE))
475 schedule_timeout_uninterruptible(1);