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 * Adjust the score by oomkilladj.
135 if (p->oomkilladj > 0)
136 points <<= p->oomkilladj;
138 points >>= -(p->oomkilladj);
142 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
143 p->pid, p->comm, points);
149 * Types of limitations to the nodes from which allocations may occur
151 #define CONSTRAINT_NONE 1
152 #define CONSTRAINT_MEMORY_POLICY 2
153 #define CONSTRAINT_CPUSET 3
156 * Determine the type of allocation constraint.
158 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
162 nodemask_t nodes = node_online_map;
164 for (z = zonelist->zones; *z; z++)
165 if (cpuset_zone_allowed(*z, gfp_mask))
166 node_clear((*z)->zone_pgdat->node_id,
169 return CONSTRAINT_CPUSET;
171 if (!nodes_empty(nodes))
172 return CONSTRAINT_MEMORY_POLICY;
175 return CONSTRAINT_NONE;
179 * Simple selection loop. We chose the process with the highest
180 * number of 'points'. We expect the caller will lock the tasklist.
182 * (not docbooked, we don't want this one cluttering up the manual)
184 static struct task_struct *select_bad_process(unsigned long *ppoints)
186 struct task_struct *g, *p;
187 struct task_struct *chosen = NULL;
188 struct timespec uptime;
191 do_posix_clock_monotonic_gettime(&uptime);
192 do_each_thread(g, p) {
193 unsigned long points;
196 /* skip the init task with pid == 1 */
199 if (p->oomkilladj == OOM_DISABLE)
201 /* If p's nodes don't overlap ours, it won't help to kill p. */
202 if (!cpuset_excl_nodes_overlap(p))
206 * This is in the process of releasing memory so wait for it
207 * to finish before killing some other task by mistake.
209 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
210 p->flags & PF_EXITING;
211 if (releasing && !(p->flags & PF_DEAD))
212 return ERR_PTR(-1UL);
213 if (p->flags & PF_SWAPOFF)
216 points = badness(p, uptime.tv_sec);
217 if (points > *ppoints || !chosen) {
221 } while_each_thread(g, p);
226 * We must be careful though to never send SIGKILL a process with
227 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
228 * we select a process with CAP_SYS_RAW_IO set).
230 static void __oom_kill_task(struct task_struct *p, const char *message)
234 printk(KERN_WARNING "tried to kill init!\n");
239 if (!p->mm || p->mm == &init_mm) {
241 printk(KERN_WARNING "tried to kill an mm-less task!\n");
246 printk(KERN_ERR "%s: Killed process %d (%s).\n",
247 message, p->pid, p->comm);
250 * We give our sacrificial lamb high priority and access to
251 * all the memory it needs. That way it should be able to
252 * exit() and clear out its resources quickly...
255 set_tsk_thread_flag(p, TIF_MEMDIE);
257 force_sig(SIGKILL, p);
260 static int oom_kill_task(struct task_struct *p, const char *message)
262 struct mm_struct *mm;
263 struct task_struct *g, *q;
267 /* WARNING: mm may not be dereferenced since we did not obtain its
268 * value from get_task_mm(p). This is OK since all we need to do is
269 * compare mm to q->mm below.
271 * Furthermore, even if mm contains a non-NULL value, p->mm may
272 * change to NULL at any time since we do not hold task_lock(p).
273 * However, this is of no concern to us.
276 if (mm == NULL || mm == &init_mm)
279 __oom_kill_task(p, message);
281 * kill all processes that share the ->mm (i.e. all threads),
282 * but are in a different thread group
285 if (q->mm == mm && q->tgid != p->tgid)
286 __oom_kill_task(q, message);
287 while_each_thread(g, q);
292 static int oom_kill_process(struct task_struct *p, unsigned long points,
295 struct task_struct *c;
296 struct list_head *tsk;
298 printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li and "
299 "children.\n", p->pid, p->comm, points);
300 /* Try to kill a child first */
301 list_for_each(tsk, &p->children) {
302 c = list_entry(tsk, struct task_struct, sibling);
305 if (!oom_kill_task(c, message))
308 return oom_kill_task(p, message);
311 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
313 int register_oom_notifier(struct notifier_block *nb)
315 return blocking_notifier_chain_register(&oom_notify_list, nb);
317 EXPORT_SYMBOL_GPL(register_oom_notifier);
319 int unregister_oom_notifier(struct notifier_block *nb)
321 return blocking_notifier_chain_unregister(&oom_notify_list, nb);
323 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
326 * out_of_memory - kill the "best" process when we run out of memory
328 * If we run out of memory, we have the choice between either
329 * killing a random task (bad), letting the system crash (worse)
330 * OR try to be smart about which process to kill. Note that we
331 * don't have to be perfect here, we just have to be good.
333 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
335 struct task_struct *p;
336 unsigned long points = 0;
337 unsigned long freed = 0;
339 blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
341 /* Got some memory back in the last second. */
344 if (printk_ratelimit()) {
345 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
352 read_lock(&tasklist_lock);
355 * Check if there were limitations on the allocation (only relevant for
356 * NUMA) that may require different handling.
358 switch (constrained_alloc(zonelist, gfp_mask)) {
359 case CONSTRAINT_MEMORY_POLICY:
360 oom_kill_process(current, points,
361 "No available memory (MPOL_BIND)");
364 case CONSTRAINT_CPUSET:
365 oom_kill_process(current, points,
366 "No available memory in cpuset");
369 case CONSTRAINT_NONE:
370 if (sysctl_panic_on_oom)
371 panic("out of memory. panic_on_oom is selected\n");
374 * Rambo mode: Shoot down a process and hope it solves whatever
375 * issues we may have.
377 p = select_bad_process(&points);
379 if (PTR_ERR(p) == -1UL)
382 /* Found nothing?!?! Either we hang forever, or we panic. */
384 read_unlock(&tasklist_lock);
386 panic("Out of memory and no killable processes...\n");
389 if (oom_kill_process(p, points, "Out of memory"))
396 read_unlock(&tasklist_lock);
400 * Give "p" a good chance of killing itself before we
401 * retry to allocate memory unless "p" is current
403 if (!test_thread_flag(TIF_MEMDIE))
404 schedule_timeout_uninterruptible(1);