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>
28 * oom_badness - calculate a numeric value for how bad this task has been
29 * @p: task struct of which task we should calculate
30 * @uptime: current uptime in seconds
32 * The formula used is relatively simple and documented inline in the
33 * function. The main rationale is that we want to select a good task
34 * to kill when we run out of memory.
36 * Good in this context means that:
37 * 1) we lose the minimum amount of work done
38 * 2) we recover a large amount of memory
39 * 3) we don't kill anything innocent of eating tons of memory
40 * 4) we want to kill the minimum amount of processes (one)
41 * 5) we try to kill the process the user expects us to kill, this
42 * algorithm has been meticulously tuned to meet the principle
43 * of least surprise ... (be careful when you change it)
46 unsigned long badness(struct task_struct
*p
, unsigned long uptime
)
48 unsigned long points
, cpu_time
, run_time
, s
;
49 struct list_head
*tsk
;
55 * The memory size of the process is the basis for the badness.
57 points
= p
->mm
->total_vm
;
60 * Processes which fork a lot of child processes are likely
61 * a good choice. We add half the vmsize of the children if they
62 * have an own mm. This prevents forking servers to flood the
63 * machine with an endless amount of children. In case a single
64 * child is eating the vast majority of memory, adding only half
65 * to the parents will make the child our kill candidate of choice.
67 list_for_each(tsk
, &p
->children
) {
68 struct task_struct
*chld
;
69 chld
= list_entry(tsk
, struct task_struct
, sibling
);
70 if (chld
->mm
!= p
->mm
&& chld
->mm
)
71 points
+= chld
->mm
->total_vm
/2 + 1;
75 * CPU time is in tens of seconds and run time is in thousands
76 * of seconds. There is no particular reason for this other than
77 * that it turned out to work very well in practice.
79 cpu_time
= (cputime_to_jiffies(p
->utime
) + cputime_to_jiffies(p
->stime
))
82 if (uptime
>= p
->start_time
.tv_sec
)
83 run_time
= (uptime
- p
->start_time
.tv_sec
) >> 10;
87 s
= int_sqrt(cpu_time
);
90 s
= int_sqrt(int_sqrt(run_time
));
95 * Niced processes are most likely less important, so double
96 * their badness points.
102 * Superuser processes are usually more important, so we make it
103 * less likely that we kill those.
105 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_ADMIN
) ||
106 p
->uid
== 0 || p
->euid
== 0)
110 * We don't want to kill a process with direct hardware access.
111 * Not only could that mess up the hardware, but usually users
112 * tend to only have this flag set on applications they think
115 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
))
119 * Adjust the score by oomkilladj.
122 if (p
->oomkilladj
> 0)
123 points
<<= p
->oomkilladj
;
125 points
>>= -(p
->oomkilladj
);
129 printk(KERN_DEBUG
"OOMkill: task %d (%s) got %d points\n",
130 p
->pid
, p
->comm
, points
);
136 * Types of limitations to the nodes from which allocations may occur
138 #define CONSTRAINT_NONE 1
139 #define CONSTRAINT_MEMORY_POLICY 2
140 #define CONSTRAINT_CPUSET 3
143 * Determine the type of allocation constraint.
145 static inline int constrained_alloc(struct zonelist
*zonelist
, gfp_t gfp_mask
)
149 nodemask_t nodes
= node_online_map
;
151 for (z
= zonelist
->zones
; *z
; z
++)
152 if (cpuset_zone_allowed(*z
, gfp_mask
))
153 node_clear((*z
)->zone_pgdat
->node_id
,
156 return CONSTRAINT_CPUSET
;
158 if (!nodes_empty(nodes
))
159 return CONSTRAINT_MEMORY_POLICY
;
162 return CONSTRAINT_NONE
;
166 * Simple selection loop. We chose the process with the highest
167 * number of 'points'. We expect the caller will lock the tasklist.
169 * (not docbooked, we don't want this one cluttering up the manual)
171 static struct task_struct
*select_bad_process(unsigned long *ppoints
)
173 struct task_struct
*g
, *p
;
174 struct task_struct
*chosen
= NULL
;
175 struct timespec uptime
;
178 do_posix_clock_monotonic_gettime(&uptime
);
179 do_each_thread(g
, p
) {
180 unsigned long points
;
183 /* skip the init task with pid == 1 */
186 if (p
->oomkilladj
== OOM_DISABLE
)
188 /* If p's nodes don't overlap ours, it won't help to kill p. */
189 if (!cpuset_excl_nodes_overlap(p
))
193 * This is in the process of releasing memory so for wait it
194 * to finish before killing some other task by mistake.
196 releasing
= test_tsk_thread_flag(p
, TIF_MEMDIE
) ||
197 p
->flags
& PF_EXITING
;
198 if (releasing
&& !(p
->flags
& PF_DEAD
))
199 return ERR_PTR(-1UL);
200 if (p
->flags
& PF_SWAPOFF
)
203 points
= badness(p
, uptime
.tv_sec
);
204 if (points
> *ppoints
|| !chosen
) {
208 } while_each_thread(g
, p
);
213 * We must be careful though to never send SIGKILL a process with
214 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
215 * we select a process with CAP_SYS_RAW_IO set).
217 static void __oom_kill_task(task_t
*p
, const char *message
)
221 printk(KERN_WARNING
"tried to kill init!\n");
226 if (!p
->mm
|| p
->mm
== &init_mm
) {
228 printk(KERN_WARNING
"tried to kill an mm-less task!\n");
233 printk(KERN_ERR
"%s: Killed process %d (%s).\n",
234 message
, p
->pid
, p
->comm
);
237 * We give our sacrificial lamb high priority and access to
238 * all the memory it needs. That way it should be able to
239 * exit() and clear out its resources quickly...
242 set_tsk_thread_flag(p
, TIF_MEMDIE
);
244 force_sig(SIGKILL
, p
);
247 static struct mm_struct
*oom_kill_task(task_t
*p
, const char *message
)
249 struct mm_struct
*mm
= get_task_mm(p
);
254 if (mm
== &init_mm
) {
259 __oom_kill_task(p
, message
);
261 * kill all processes that share the ->mm (i.e. all threads),
262 * but are in a different thread group
265 if (q
->mm
== mm
&& q
->tgid
!= p
->tgid
)
266 __oom_kill_task(q
, message
);
267 while_each_thread(g
, q
);
272 static struct mm_struct
*oom_kill_process(struct task_struct
*p
,
273 unsigned long points
, const char *message
)
275 struct mm_struct
*mm
;
276 struct task_struct
*c
;
277 struct list_head
*tsk
;
279 printk(KERN_ERR
"Out of Memory: Kill process %d (%s) score %li and "
280 "children.\n", p
->pid
, p
->comm
, points
);
281 /* Try to kill a child first */
282 list_for_each(tsk
, &p
->children
) {
283 c
= list_entry(tsk
, struct task_struct
, sibling
);
286 mm
= oom_kill_task(c
, message
);
290 return oom_kill_task(p
, message
);
294 * oom_kill - kill the "best" process when we run out of memory
296 * If we run out of memory, we have the choice between either
297 * killing a random task (bad), letting the system crash (worse)
298 * OR try to be smart about which process to kill. Note that we
299 * don't have to be perfect here, we just have to be good.
301 void out_of_memory(struct zonelist
*zonelist
, gfp_t gfp_mask
, int order
)
303 struct mm_struct
*mm
= NULL
;
305 unsigned long points
= 0;
307 if (printk_ratelimit()) {
308 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
315 read_lock(&tasklist_lock
);
318 * Check if there were limitations on the allocation (only relevant for
319 * NUMA) that may require different handling.
321 switch (constrained_alloc(zonelist
, gfp_mask
)) {
322 case CONSTRAINT_MEMORY_POLICY
:
323 mm
= oom_kill_process(current
, points
,
324 "No available memory (MPOL_BIND)");
327 case CONSTRAINT_CPUSET
:
328 mm
= oom_kill_process(current
, points
,
329 "No available memory in cpuset");
332 case CONSTRAINT_NONE
:
335 * Rambo mode: Shoot down a process and hope it solves whatever
336 * issues we may have.
338 p
= select_bad_process(&points
);
340 if (PTR_ERR(p
) == -1UL)
343 /* Found nothing?!?! Either we hang forever, or we panic. */
345 read_unlock(&tasklist_lock
);
347 panic("Out of memory and no killable processes...\n");
350 mm
= oom_kill_process(p
, points
, "Out of memory");
363 * Give "p" a good chance of killing itself before we
364 * retry to allocate memory unless "p" is current
366 if (!test_thread_flag(TIF_MEMDIE
))
367 schedule_timeout_interruptible(1);