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Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
2 * linux/mm/oom_kill.c
3 *
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...
7 *
8 * The routines in this file are used to kill a process when
Paul Jacksona49335c2005-09-06 15:18:09 -07009 * 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.
Linus Torvalds1da177e2005-04-16 15:20:36 -070011 *
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.
16 */
17
18#include <linux/mm.h>
19#include <linux/sched.h>
20#include <linux/swap.h>
21#include <linux/timex.h>
22#include <linux/jiffies.h>
Paul Jacksonef08e3b2005-09-06 15:18:13 -070023#include <linux/cpuset.h>
Linus Torvalds1da177e2005-04-16 15:20:36 -070024
25/* #define DEBUG */
26
27/**
28 * oom_badness - calculate a numeric value for how bad this task has been
29 * @p: task struct of which task we should calculate
Paul Jacksona49335c2005-09-06 15:18:09 -070030 * @uptime: current uptime in seconds
Linus Torvalds1da177e2005-04-16 15:20:36 -070031 *
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.
35 *
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)
44 */
45
46unsigned long badness(struct task_struct *p, unsigned long uptime)
47{
48 unsigned long points, cpu_time, run_time, s;
49 struct list_head *tsk;
50
51 if (!p->mm)
52 return 0;
53
54 /*
55 * The memory size of the process is the basis for the badness.
56 */
57 points = p->mm->total_vm;
58
59 /*
60 * Processes which fork a lot of child processes are likely
Paul Jacksona49335c2005-09-06 15:18:09 -070061 * a good choice. We add the vmsize of the children if they
Linus Torvalds1da177e2005-04-16 15:20:36 -070062 * have an own mm. This prevents forking servers to flood the
Paul Jacksona49335c2005-09-06 15:18:09 -070063 * machine with an endless amount of children
Linus Torvalds1da177e2005-04-16 15:20:36 -070064 */
65 list_for_each(tsk, &p->children) {
66 struct task_struct *chld;
67 chld = list_entry(tsk, struct task_struct, sibling);
68 if (chld->mm != p->mm && chld->mm)
69 points += chld->mm->total_vm;
70 }
71
72 /*
73 * CPU time is in tens of seconds and run time is in thousands
74 * of seconds. There is no particular reason for this other than
75 * that it turned out to work very well in practice.
76 */
77 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
78 >> (SHIFT_HZ + 3);
79
80 if (uptime >= p->start_time.tv_sec)
81 run_time = (uptime - p->start_time.tv_sec) >> 10;
82 else
83 run_time = 0;
84
85 s = int_sqrt(cpu_time);
86 if (s)
87 points /= s;
88 s = int_sqrt(int_sqrt(run_time));
89 if (s)
90 points /= s;
91
92 /*
93 * Niced processes are most likely less important, so double
94 * their badness points.
95 */
96 if (task_nice(p) > 0)
97 points *= 2;
98
99 /*
100 * Superuser processes are usually more important, so we make it
101 * less likely that we kill those.
102 */
103 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
104 p->uid == 0 || p->euid == 0)
105 points /= 4;
106
107 /*
108 * We don't want to kill a process with direct hardware access.
109 * Not only could that mess up the hardware, but usually users
110 * tend to only have this flag set on applications they think
111 * of as important.
112 */
113 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
114 points /= 4;
115
116 /*
117 * Adjust the score by oomkilladj.
118 */
119 if (p->oomkilladj) {
120 if (p->oomkilladj > 0)
121 points <<= p->oomkilladj;
122 else
123 points >>= -(p->oomkilladj);
124 }
125
126#ifdef DEBUG
127 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
128 p->pid, p->comm, points);
129#endif
130 return points;
131}
132
133/*
134 * Simple selection loop. We chose the process with the highest
135 * number of 'points'. We expect the caller will lock the tasklist.
136 *
137 * (not docbooked, we don't want this one cluttering up the manual)
138 */
139static struct task_struct * select_bad_process(void)
140{
141 unsigned long maxpoints = 0;
142 struct task_struct *g, *p;
143 struct task_struct *chosen = NULL;
144 struct timespec uptime;
145
146 do_posix_clock_monotonic_gettime(&uptime);
Paul Jacksona49335c2005-09-06 15:18:09 -0700147 do_each_thread(g, p) {
148 unsigned long points;
149 int releasing;
150
Linus Torvalds1da177e2005-04-16 15:20:36 -0700151 /* skip the init task with pid == 1 */
Paul Jacksona49335c2005-09-06 15:18:09 -0700152 if (p->pid == 1)
153 continue;
154 if (p->oomkilladj == OOM_DISABLE)
155 continue;
Paul Jacksonef08e3b2005-09-06 15:18:13 -0700156 /* If p's nodes don't overlap ours, it won't help to kill p. */
157 if (!cpuset_excl_nodes_overlap(p))
158 continue;
159
Paul Jacksona49335c2005-09-06 15:18:09 -0700160 /*
161 * This is in the process of releasing memory so for wait it
162 * to finish before killing some other task by mistake.
163 */
164 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
165 p->flags & PF_EXITING;
166 if (releasing && !(p->flags & PF_DEAD))
167 return ERR_PTR(-1UL);
168 if (p->flags & PF_SWAPOFF)
169 return p;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700170
Paul Jacksona49335c2005-09-06 15:18:09 -0700171 points = badness(p, uptime.tv_sec);
172 if (points > maxpoints || !chosen) {
173 chosen = p;
174 maxpoints = points;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700175 }
Paul Jacksona49335c2005-09-06 15:18:09 -0700176 } while_each_thread(g, p);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700177 return chosen;
178}
179
180/**
181 * We must be careful though to never send SIGKILL a process with
182 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
183 * we select a process with CAP_SYS_RAW_IO set).
184 */
185static void __oom_kill_task(task_t *p)
186{
187 if (p->pid == 1) {
188 WARN_ON(1);
189 printk(KERN_WARNING "tried to kill init!\n");
190 return;
191 }
192
193 task_lock(p);
194 if (!p->mm || p->mm == &init_mm) {
195 WARN_ON(1);
196 printk(KERN_WARNING "tried to kill an mm-less task!\n");
197 task_unlock(p);
198 return;
199 }
200 task_unlock(p);
Paul Jacksona49335c2005-09-06 15:18:09 -0700201 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n",
202 p->pid, p->comm);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700203
204 /*
205 * We give our sacrificial lamb high priority and access to
206 * all the memory it needs. That way it should be able to
207 * exit() and clear out its resources quickly...
208 */
209 p->time_slice = HZ;
210 set_tsk_thread_flag(p, TIF_MEMDIE);
211
212 force_sig(SIGKILL, p);
213}
214
215static struct mm_struct *oom_kill_task(task_t *p)
216{
217 struct mm_struct *mm = get_task_mm(p);
218 task_t * g, * q;
219
220 if (!mm)
221 return NULL;
222 if (mm == &init_mm) {
223 mmput(mm);
224 return NULL;
225 }
226
227 __oom_kill_task(p);
228 /*
229 * kill all processes that share the ->mm (i.e. all threads),
230 * but are in a different thread group
231 */
232 do_each_thread(g, q)
233 if (q->mm == mm && q->tgid != p->tgid)
234 __oom_kill_task(q);
235 while_each_thread(g, q);
236
237 return mm;
238}
239
240static struct mm_struct *oom_kill_process(struct task_struct *p)
241{
242 struct mm_struct *mm;
243 struct task_struct *c;
244 struct list_head *tsk;
245
246 /* Try to kill a child first */
247 list_for_each(tsk, &p->children) {
248 c = list_entry(tsk, struct task_struct, sibling);
249 if (c->mm == p->mm)
250 continue;
251 mm = oom_kill_task(c);
252 if (mm)
253 return mm;
254 }
255 return oom_kill_task(p);
256}
257
258/**
259 * oom_kill - kill the "best" process when we run out of memory
260 *
261 * If we run out of memory, we have the choice between either
262 * killing a random task (bad), letting the system crash (worse)
263 * OR try to be smart about which process to kill. Note that we
264 * don't have to be perfect here, we just have to be good.
265 */
Marcelo Tosatti79b9ce32005-07-07 17:56:04 -0700266void out_of_memory(unsigned int __nocast gfp_mask, int order)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700267{
268 struct mm_struct *mm = NULL;
269 task_t * p;
270
Anton Blanchard42639262005-07-07 17:56:06 -0700271 if (printk_ratelimit()) {
272 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
273 gfp_mask, order);
274 show_mem();
275 }
Janet Morgan578c2fd2005-06-21 17:14:56 -0700276
Linus Torvalds1da177e2005-04-16 15:20:36 -0700277 read_lock(&tasklist_lock);
278retry:
279 p = select_bad_process();
280
281 if (PTR_ERR(p) == -1UL)
282 goto out;
283
284 /* Found nothing?!?! Either we hang forever, or we panic. */
285 if (!p) {
286 read_unlock(&tasklist_lock);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700287 panic("Out of memory and no killable processes...\n");
288 }
289
Linus Torvalds1da177e2005-04-16 15:20:36 -0700290 mm = oom_kill_process(p);
291 if (!mm)
292 goto retry;
293
294 out:
295 read_unlock(&tasklist_lock);
296 if (mm)
297 mmput(mm);
298
299 /*
300 * Give "p" a good chance of killing itself before we
301 * retry to allocate memory.
302 */
303 __set_current_state(TASK_INTERRUPTIBLE);
304 schedule_timeout(1);
305}