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);