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 __alloc_pages()
10 * in mm/page_alloc.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 #include <linux/cpuset.h>
24
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
30 * @uptime: current uptime in seconds
31 *
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
46 unsigned 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
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.
66 */
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;
72 }
73
74 /*
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.
78 */
79 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
80 >> (SHIFT_HZ + 3);
81
82 if (uptime >= p->start_time.tv_sec)
83 run_time = (uptime - p->start_time.tv_sec) >> 10;
84 else
85 run_time = 0;
86
87 s = int_sqrt(cpu_time);
88 if (s)
89 points /= s;
90 s = int_sqrt(int_sqrt(run_time));
91 if (s)
92 points /= s;
93
94 /*
95 * Niced processes are most likely less important, so double
96 * their badness points.
97 */
98 if (task_nice(p) > 0)
99 points *= 2;
100
101 /*
102 * Superuser processes are usually more important, so we make it
103 * less likely that we kill those.
104 */
105 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
106 p->uid == 0 || p->euid == 0)
107 points /= 4;
108
109 /*
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
113 * of as important.
114 */
115 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
116 points /= 4;
117
118 /*
119 * Adjust the score by oomkilladj.
120 */
121 if (p->oomkilladj) {
122 if (p->oomkilladj > 0)
123 points <<= p->oomkilladj;
124 else
125 points >>= -(p->oomkilladj);
126 }
127
128 #ifdef DEBUG
129 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
130 p->pid, p->comm, points);
131 #endif
132 return points;
133 }
134
135 /*
136 * Types of limitations to the nodes from which allocations may occur
137 */
138 #define CONSTRAINT_NONE 1
139 #define CONSTRAINT_MEMORY_POLICY 2
140 #define CONSTRAINT_CPUSET 3
141
142 /*
143 * Determine the type of allocation constraint.
144 */
145 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
146 {
147 #ifdef CONFIG_NUMA
148 struct zone **z;
149 nodemask_t nodes = node_online_map;
150
151 for (z = zonelist->zones; *z; z++)
152 if (cpuset_zone_allowed(*z, gfp_mask))
153 node_clear((*z)->zone_pgdat->node_id,
154 nodes);
155 else
156 return CONSTRAINT_CPUSET;
157
158 if (!nodes_empty(nodes))
159 return CONSTRAINT_MEMORY_POLICY;
160 #endif
161
162 return CONSTRAINT_NONE;
163 }
164
165 /*
166 * Simple selection loop. We chose the process with the highest
167 * number of 'points'. We expect the caller will lock the tasklist.
168 *
169 * (not docbooked, we don't want this one cluttering up the manual)
170 */
171 static struct task_struct *select_bad_process(unsigned long *ppoints)
172 {
173 struct task_struct *g, *p;
174 struct task_struct *chosen = NULL;
175 struct timespec uptime;
176 *ppoints = 0;
177
178 do_posix_clock_monotonic_gettime(&uptime);
179 do_each_thread(g, p) {
180 unsigned long points;
181 int releasing;
182
183 /* skip the init task with pid == 1 */
184 if (p->pid == 1)
185 continue;
186 if (p->oomkilladj == OOM_DISABLE)
187 continue;
188 /* If p's nodes don't overlap ours, it won't help to kill p. */
189 if (!cpuset_excl_nodes_overlap(p))
190 continue;
191
192 /*
193 * This is in the process of releasing memory so for wait it
194 * to finish before killing some other task by mistake.
195 */
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)
201 return p;
202
203 points = badness(p, uptime.tv_sec);
204 if (points > *ppoints || !chosen) {
205 chosen = p;
206 *ppoints = points;
207 }
208 } while_each_thread(g, p);
209 return chosen;
210 }
211
212 /**
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).
216 */
217 static void __oom_kill_task(task_t *p, const char *message)
218 {
219 if (p->pid == 1) {
220 WARN_ON(1);
221 printk(KERN_WARNING "tried to kill init!\n");
222 return;
223 }
224
225 task_lock(p);
226 if (!p->mm || p->mm == &init_mm) {
227 WARN_ON(1);
228 printk(KERN_WARNING "tried to kill an mm-less task!\n");
229 task_unlock(p);
230 return;
231 }
232 task_unlock(p);
233 printk(KERN_ERR "%s: Killed process %d (%s).\n",
234 message, p->pid, p->comm);
235
236 /*
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...
240 */
241 p->time_slice = HZ;
242 set_tsk_thread_flag(p, TIF_MEMDIE);
243
244 force_sig(SIGKILL, p);
245 }
246
247 static struct mm_struct *oom_kill_task(task_t *p, const char *message)
248 {
249 struct mm_struct *mm = get_task_mm(p);
250 task_t * g, * q;
251
252 if (!mm)
253 return NULL;
254 if (mm == &init_mm) {
255 mmput(mm);
256 return NULL;
257 }
258
259 __oom_kill_task(p, message);
260 /*
261 * kill all processes that share the ->mm (i.e. all threads),
262 * but are in a different thread group
263 */
264 do_each_thread(g, q)
265 if (q->mm == mm && q->tgid != p->tgid)
266 __oom_kill_task(q, message);
267 while_each_thread(g, q);
268
269 return mm;
270 }
271
272 static struct mm_struct *oom_kill_process(struct task_struct *p,
273 unsigned long points, const char *message)
274 {
275 struct mm_struct *mm;
276 struct task_struct *c;
277 struct list_head *tsk;
278
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);
284 if (c->mm == p->mm)
285 continue;
286 mm = oom_kill_task(c, message);
287 if (mm)
288 return mm;
289 }
290 return oom_kill_task(p, message);
291 }
292
293 /**
294 * oom_kill - kill the "best" process when we run out of memory
295 *
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.
300 */
301 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
302 {
303 struct mm_struct *mm = NULL;
304 task_t *p;
305 unsigned long points = 0;
306
307 if (printk_ratelimit()) {
308 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
309 gfp_mask, order);
310 dump_stack();
311 show_mem();
312 }
313
314 cpuset_lock();
315 read_lock(&tasklist_lock);
316
317 /*
318 * Check if there were limitations on the allocation (only relevant for
319 * NUMA) that may require different handling.
320 */
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)");
325 break;
326
327 case CONSTRAINT_CPUSET:
328 mm = oom_kill_process(current, points,
329 "No available memory in cpuset");
330 break;
331
332 case CONSTRAINT_NONE:
333 retry:
334 /*
335 * Rambo mode: Shoot down a process and hope it solves whatever
336 * issues we may have.
337 */
338 p = select_bad_process(&points);
339
340 if (PTR_ERR(p) == -1UL)
341 goto out;
342
343 /* Found nothing?!?! Either we hang forever, or we panic. */
344 if (!p) {
345 read_unlock(&tasklist_lock);
346 cpuset_unlock();
347 panic("Out of memory and no killable processes...\n");
348 }
349
350 mm = oom_kill_process(p, points, "Out of memory");
351 if (!mm)
352 goto retry;
353
354 break;
355 }
356
357 out:
358 read_unlock(&tasklist_lock);
359 cpuset_unlock();
360 if (mm)
361 mmput(mm);
362
363 /*
364 * Give "p" a good chance of killing itself before we
365 * retry to allocate memory unless "p" is current
366 */
367 if (!test_thread_flag(TIF_MEMDIE))
368 schedule_timeout_uninterruptible(1);
369 }
370
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