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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/sched.h>
21 #include <linux/swap.h>
22 #include <linux/timex.h>
23 #include <linux/jiffies.h>
24 #include <linux/cpuset.h>
25 #include <linux/module.h>
26 #include <linux/notifier.h>
28 int sysctl_panic_on_oom
;
32 * badness - calculate a numeric value for how bad this task has been
33 * @p: task struct of which task we should calculate
34 * @uptime: current uptime in seconds
36 * The formula used is relatively simple and documented inline in the
37 * function. The main rationale is that we want to select a good task
38 * to kill when we run out of memory.
40 * Good in this context means that:
41 * 1) we lose the minimum amount of work done
42 * 2) we recover a large amount of memory
43 * 3) we don't kill anything innocent of eating tons of memory
44 * 4) we want to kill the minimum amount of processes (one)
45 * 5) we try to kill the process the user expects us to kill, this
46 * algorithm has been meticulously tuned to meet the principle
47 * of least surprise ... (be careful when you change it)
50 unsigned long badness(struct task_struct
*p
, unsigned long uptime
)
52 unsigned long points
, cpu_time
, run_time
, s
;
54 struct task_struct
*child
;
64 * The memory size of the process is the basis for the badness.
66 points
= mm
->total_vm
;
69 * After this unlock we can no longer dereference local variable `mm'
74 * swapoff can easily use up all memory, so kill those first.
76 if (p
->flags
& PF_SWAPOFF
)
80 * Processes which fork a lot of child processes are likely
81 * a good choice. We add half the vmsize of the children if they
82 * have an own mm. This prevents forking servers to flood the
83 * machine with an endless amount of children. In case a single
84 * child is eating the vast majority of memory, adding only half
85 * to the parents will make the child our kill candidate of choice.
87 list_for_each_entry(child
, &p
->children
, sibling
) {
89 if (child
->mm
!= mm
&& child
->mm
)
90 points
+= child
->mm
->total_vm
/2 + 1;
95 * CPU time is in tens of seconds and run time is in thousands
96 * of seconds. There is no particular reason for this other than
97 * that it turned out to work very well in practice.
99 cpu_time
= (cputime_to_jiffies(p
->utime
) + cputime_to_jiffies(p
->stime
))
102 if (uptime
>= p
->start_time
.tv_sec
)
103 run_time
= (uptime
- p
->start_time
.tv_sec
) >> 10;
107 s
= int_sqrt(cpu_time
);
110 s
= int_sqrt(int_sqrt(run_time
));
115 * Niced processes are most likely less important, so double
116 * their badness points.
118 if (task_nice(p
) > 0)
122 * Superuser processes are usually more important, so we make it
123 * less likely that we kill those.
125 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_ADMIN
) ||
126 p
->uid
== 0 || p
->euid
== 0)
130 * We don't want to kill a process with direct hardware access.
131 * Not only could that mess up the hardware, but usually users
132 * tend to only have this flag set on applications they think
135 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
))
139 * If p's nodes don't overlap ours, it may still help to kill p
140 * because p may have allocated or otherwise mapped memory on
141 * this node before. However it will be less likely.
143 if (!cpuset_excl_nodes_overlap(p
))
147 * Adjust the score by oomkilladj.
150 if (p
->oomkilladj
> 0)
151 points
<<= p
->oomkilladj
;
153 points
>>= -(p
->oomkilladj
);
157 printk(KERN_DEBUG
"OOMkill: task %d (%s) got %d points\n",
158 p
->pid
, p
->comm
, points
);
164 * Types of limitations to the nodes from which allocations may occur
166 #define CONSTRAINT_NONE 1
167 #define CONSTRAINT_MEMORY_POLICY 2
168 #define CONSTRAINT_CPUSET 3
171 * Determine the type of allocation constraint.
173 static inline int constrained_alloc(struct zonelist
*zonelist
, gfp_t gfp_mask
)
179 /* node has memory ? */
180 for_each_online_node(node
)
181 if (NODE_DATA(node
)->node_present_pages
)
182 node_set(node
, nodes
);
184 for (z
= zonelist
->zones
; *z
; z
++)
185 if (cpuset_zone_allowed_softwall(*z
, gfp_mask
))
186 node_clear(zone_to_nid(*z
), nodes
);
188 return CONSTRAINT_CPUSET
;
190 if (!nodes_empty(nodes
))
191 return CONSTRAINT_MEMORY_POLICY
;
194 return CONSTRAINT_NONE
;
198 * Simple selection loop. We chose the process with the highest
199 * number of 'points'. We expect the caller will lock the tasklist.
201 * (not docbooked, we don't want this one cluttering up the manual)
203 static struct task_struct
*select_bad_process(unsigned long *ppoints
)
205 struct task_struct
*g
, *p
;
206 struct task_struct
*chosen
= NULL
;
207 struct timespec uptime
;
210 do_posix_clock_monotonic_gettime(&uptime
);
211 do_each_thread(g
, p
) {
212 unsigned long points
;
215 * skip kernel threads and tasks which have already released
220 /* skip the init task */
225 * This task already has access to memory reserves and is
226 * being killed. Don't allow any other task access to the
229 * Note: this may have a chance of deadlock if it gets
230 * blocked waiting for another task which itself is waiting
231 * for memory. Is there a better alternative?
233 if (test_tsk_thread_flag(p
, TIF_MEMDIE
))
234 return ERR_PTR(-1UL);
237 * This is in the process of releasing memory so wait for it
238 * to finish before killing some other task by mistake.
240 * However, if p is the current task, we allow the 'kill' to
241 * go ahead if it is exiting: this will simply set TIF_MEMDIE,
242 * which will allow it to gain access to memory reserves in
243 * the process of exiting and releasing its resources.
244 * Otherwise we could get an easy OOM deadlock.
246 if (p
->flags
& PF_EXITING
) {
248 return ERR_PTR(-1UL);
251 *ppoints
= ULONG_MAX
;
254 if (p
->oomkilladj
== OOM_DISABLE
)
257 points
= badness(p
, uptime
.tv_sec
);
258 if (points
> *ppoints
|| !chosen
) {
262 } while_each_thread(g
, p
);
268 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
269 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
272 static void __oom_kill_task(struct task_struct
*p
, int verbose
)
276 printk(KERN_WARNING
"tried to kill init!\n");
282 printk(KERN_WARNING
"tried to kill an mm-less task!\n");
287 printk(KERN_ERR
"Killed process %d (%s)\n", p
->pid
, p
->comm
);
290 * We give our sacrificial lamb high priority and access to
291 * all the memory it needs. That way it should be able to
292 * exit() and clear out its resources quickly...
295 set_tsk_thread_flag(p
, TIF_MEMDIE
);
297 force_sig(SIGKILL
, p
);
300 static int oom_kill_task(struct task_struct
*p
)
302 struct mm_struct
*mm
;
303 struct task_struct
*g
, *q
;
307 /* WARNING: mm may not be dereferenced since we did not obtain its
308 * value from get_task_mm(p). This is OK since all we need to do is
309 * compare mm to q->mm below.
311 * Furthermore, even if mm contains a non-NULL value, p->mm may
312 * change to NULL at any time since we do not hold task_lock(p).
313 * However, this is of no concern to us.
320 * Don't kill the process if any threads are set to OOM_DISABLE
322 do_each_thread(g
, q
) {
323 if (q
->mm
== mm
&& q
->oomkilladj
== OOM_DISABLE
)
325 } while_each_thread(g
, q
);
327 __oom_kill_task(p
, 1);
330 * kill all processes that share the ->mm (i.e. all threads),
331 * but are in a different thread group. Don't let them have access
332 * to memory reserves though, otherwise we might deplete all memory.
334 do_each_thread(g
, q
) {
335 if (q
->mm
== mm
&& q
->tgid
!= p
->tgid
)
336 force_sig(SIGKILL
, p
);
337 } while_each_thread(g
, q
);
342 static int oom_kill_process(struct task_struct
*p
, unsigned long points
,
345 struct task_struct
*c
;
346 struct list_head
*tsk
;
349 * If the task is already exiting, don't alarm the sysadmin or kill
350 * its children or threads, just set TIF_MEMDIE so it can die quickly
352 if (p
->flags
& PF_EXITING
) {
353 __oom_kill_task(p
, 0);
357 printk(KERN_ERR
"%s: kill process %d (%s) score %li or a child\n",
358 message
, p
->pid
, p
->comm
, points
);
360 /* Try to kill a child first */
361 list_for_each(tsk
, &p
->children
) {
362 c
= list_entry(tsk
, struct task_struct
, sibling
);
365 if (!oom_kill_task(c
))
368 return oom_kill_task(p
);
371 static BLOCKING_NOTIFIER_HEAD(oom_notify_list
);
373 int register_oom_notifier(struct notifier_block
*nb
)
375 return blocking_notifier_chain_register(&oom_notify_list
, nb
);
377 EXPORT_SYMBOL_GPL(register_oom_notifier
);
379 int unregister_oom_notifier(struct notifier_block
*nb
)
381 return blocking_notifier_chain_unregister(&oom_notify_list
, nb
);
383 EXPORT_SYMBOL_GPL(unregister_oom_notifier
);
386 * out_of_memory - kill the "best" process when we run out of memory
388 * If we run out of memory, we have the choice between either
389 * killing a random task (bad), letting the system crash (worse)
390 * OR try to be smart about which process to kill. Note that we
391 * don't have to be perfect here, we just have to be good.
393 void out_of_memory(struct zonelist
*zonelist
, gfp_t gfp_mask
, int order
)
395 struct task_struct
*p
;
396 unsigned long points
= 0;
397 unsigned long freed
= 0;
399 blocking_notifier_call_chain(&oom_notify_list
, 0, &freed
);
401 /* Got some memory back in the last second. */
404 if (printk_ratelimit()) {
405 printk(KERN_WARNING
"%s invoked oom-killer: "
406 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
407 current
->comm
, gfp_mask
, order
, current
->oomkilladj
);
413 read_lock(&tasklist_lock
);
416 * Check if there were limitations on the allocation (only relevant for
417 * NUMA) that may require different handling.
419 switch (constrained_alloc(zonelist
, gfp_mask
)) {
420 case CONSTRAINT_MEMORY_POLICY
:
421 oom_kill_process(current
, points
,
422 "No available memory (MPOL_BIND)");
425 case CONSTRAINT_CPUSET
:
426 oom_kill_process(current
, points
,
427 "No available memory in cpuset");
430 case CONSTRAINT_NONE
:
431 if (sysctl_panic_on_oom
)
432 panic("out of memory. panic_on_oom is selected\n");
435 * Rambo mode: Shoot down a process and hope it solves whatever
436 * issues we may have.
438 p
= select_bad_process(&points
);
440 if (PTR_ERR(p
) == -1UL)
443 /* Found nothing?!?! Either we hang forever, or we panic. */
445 read_unlock(&tasklist_lock
);
447 panic("Out of memory and no killable processes...\n");
450 if (oom_kill_process(p
, points
, "Out of memory"))
457 read_unlock(&tasklist_lock
);
461 * Give "p" a good chance of killing itself before we
462 * retry to allocate memory unless "p" is current
464 if (!test_thread_flag(TIF_MEMDIE
))
465 schedule_timeout_uninterruptible(1);