1 /*
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
9 * we're seriously out of memory. This gets called from kswapd()
10 * in linux/mm/vmscan.c when we really run out of memory.
11 *
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>
23
24 /* #define DEBUG */
25
26 /**
27 * oom_badness - calculate a numeric value for how bad this task has been
28 * @p: task struct of which task we should calculate
29 * @p: current uptime in seconds
30 *
31 * The formula used is relatively simple and documented inline in the
32 * function. The main rationale is that we want to select a good task
33 * to kill when we run out of memory.
34 *
35 * Good in this context means that:
36 * 1) we lose the minimum amount of work done
37 * 2) we recover a large amount of memory
38 * 3) we don't kill anything innocent of eating tons of memory
39 * 4) we want to kill the minimum amount of processes (one)
40 * 5) we try to kill the process the user expects us to kill, this
41 * algorithm has been meticulously tuned to meet the principle
42 * of least surprise ... (be careful when you change it)
43 */
44
45 unsigned long badness(struct task_struct *p, unsigned long uptime)
46 {
47 unsigned long points, cpu_time, run_time, s;
48 struct list_head *tsk;
49
50 if (!p->mm)
51 return 0;
52
53 /*
54 * The memory size of the process is the basis for the badness.
55 */
56 points = p->mm->total_vm;
57
58 /*
59 * Processes which fork a lot of child processes are likely
60 * a good choice. We add the vmsize of the childs if they
61 * have an own mm. This prevents forking servers to flood the
62 * machine with an endless amount of childs
63 */
64 list_for_each(tsk, &p->children) {
65 struct task_struct *chld;
66 chld = list_entry(tsk, struct task_struct, sibling);
67 if (chld->mm != p->mm && chld->mm)
68 points += chld->mm->total_vm;
69 }
70
71 /*
72 * CPU time is in tens of seconds and run time is in thousands
73 * of seconds. There is no particular reason for this other than
74 * that it turned out to work very well in practice.
75 */
76 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
77 >> (SHIFT_HZ + 3);
78
79 if (uptime >= p->start_time.tv_sec)
80 run_time = (uptime - p->start_time.tv_sec) >> 10;
81 else
82 run_time = 0;
83
84 s = int_sqrt(cpu_time);
85 if (s)
86 points /= s;
87 s = int_sqrt(int_sqrt(run_time));
88 if (s)
89 points /= s;
90
91 /*
92 * Niced processes are most likely less important, so double
93 * their badness points.
94 */
95 if (task_nice(p) > 0)
96 points *= 2;
97
98 /*
99 * Superuser processes are usually more important, so we make it
100 * less likely that we kill those.
101 */
102 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
103 p->uid == 0 || p->euid == 0)
104 points /= 4;
105
106 /*
107 * We don't want to kill a process with direct hardware access.
108 * Not only could that mess up the hardware, but usually users
109 * tend to only have this flag set on applications they think
110 * of as important.
111 */
112 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
113 points /= 4;
114
115 /*
116 * Adjust the score by oomkilladj.
117 */
118 if (p->oomkilladj) {
119 if (p->oomkilladj > 0)
120 points <<= p->oomkilladj;
121 else
122 points >>= -(p->oomkilladj);
123 }
124
125 #ifdef DEBUG
126 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
127 p->pid, p->comm, points);
128 #endif
129 return points;
130 }
131
132 /*
133 * Simple selection loop. We chose the process with the highest
134 * number of 'points'. We expect the caller will lock the tasklist.
135 *
136 * (not docbooked, we don't want this one cluttering up the manual)
137 */
138 static struct task_struct * select_bad_process(void)
139 {
140 unsigned long maxpoints = 0;
141 struct task_struct *g, *p;
142 struct task_struct *chosen = NULL;
143 struct timespec uptime;
144
145 do_posix_clock_monotonic_gettime(&uptime);
146 do_each_thread(g, p)
147 /* skip the init task with pid == 1 */
148 if (p->pid > 1) {
149 unsigned long points;
150
151 /*
152 * This is in the process of releasing memory so wait it
153 * to finish before killing some other task by mistake.
154 */
155 if ((unlikely(test_tsk_thread_flag(p, TIF_MEMDIE)) || (p->flags & PF_EXITING)) &&
156 !(p->flags & PF_DEAD))
157 return ERR_PTR(-1UL);
158 if (p->flags & PF_SWAPOFF)
159 return p;
160
161 points = badness(p, uptime.tv_sec);
162 if (points > maxpoints || !chosen) {
163 chosen = p;
164 maxpoints = points;
165 }
166 }
167 while_each_thread(g, p);
168 return chosen;
169 }
170
171 /**
172 * We must be careful though to never send SIGKILL a process with
173 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
174 * we select a process with CAP_SYS_RAW_IO set).
175 */
176 static void __oom_kill_task(task_t *p)
177 {
178 if (p->pid == 1) {
179 WARN_ON(1);
180 printk(KERN_WARNING "tried to kill init!\n");
181 return;
182 }
183
184 task_lock(p);
185 if (!p->mm || p->mm == &init_mm) {
186 WARN_ON(1);
187 printk(KERN_WARNING "tried to kill an mm-less task!\n");
188 task_unlock(p);
189 return;
190 }
191 task_unlock(p);
192 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", p->pid, p->comm);
193
194 /*
195 * We give our sacrificial lamb high priority and access to
196 * all the memory it needs. That way it should be able to
197 * exit() and clear out its resources quickly...
198 */
199 p->time_slice = HZ;
200 set_tsk_thread_flag(p, TIF_MEMDIE);
201
202 force_sig(SIGKILL, p);
203 }
204
205 static struct mm_struct *oom_kill_task(task_t *p)
206 {
207 struct mm_struct *mm = get_task_mm(p);
208 task_t * g, * q;
209
210 if (!mm)
211 return NULL;
212 if (mm == &init_mm) {
213 mmput(mm);
214 return NULL;
215 }
216
217 __oom_kill_task(p);
218 /*
219 * kill all processes that share the ->mm (i.e. all threads),
220 * but are in a different thread group
221 */
222 do_each_thread(g, q)
223 if (q->mm == mm && q->tgid != p->tgid)
224 __oom_kill_task(q);
225 while_each_thread(g, q);
226
227 return mm;
228 }
229
230 static struct mm_struct *oom_kill_process(struct task_struct *p)
231 {
232 struct mm_struct *mm;
233 struct task_struct *c;
234 struct list_head *tsk;
235
236 /* Try to kill a child first */
237 list_for_each(tsk, &p->children) {
238 c = list_entry(tsk, struct task_struct, sibling);
239 if (c->mm == p->mm)
240 continue;
241 mm = oom_kill_task(c);
242 if (mm)
243 return mm;
244 }
245 return oom_kill_task(p);
246 }
247
248 /**
249 * oom_kill - kill the "best" process when we run out of memory
250 *
251 * If we run out of memory, we have the choice between either
252 * killing a random task (bad), letting the system crash (worse)
253 * OR try to be smart about which process to kill. Note that we
254 * don't have to be perfect here, we just have to be good.
255 */
256 void out_of_memory(int gfp_mask)
257 {
258 struct mm_struct *mm = NULL;
259 task_t * p;
260
261 read_lock(&tasklist_lock);
262 retry:
263 p = select_bad_process();
264
265 if (PTR_ERR(p) == -1UL)
266 goto out;
267
268 /* Found nothing?!?! Either we hang forever, or we panic. */
269 if (!p) {
270 read_unlock(&tasklist_lock);
271 show_free_areas();
272 panic("Out of memory and no killable processes...\n");
273 }
274
275 printk("oom-killer: gfp_mask=0x%x\n", gfp_mask);
276 show_free_areas();
277 mm = oom_kill_process(p);
278 if (!mm)
279 goto retry;
280
281 out:
282 read_unlock(&tasklist_lock);
283 if (mm)
284 mmput(mm);
285
286 /*
287 * Give "p" a good chance of killing itself before we
288 * retry to allocate memory.
289 */
290 __set_current_state(TASK_INTERRUPTIBLE);
291 schedule_timeout(1);
292 }
293
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