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;
50 struct task_struct *child;
60 * The memory size of the process is the basis for the badness.
62 points = mm->total_vm;
65 * After this unlock we can no longer dereference local variable `mm'
70 * Processes which fork a lot of child processes are likely
71 * a good choice. We add half the vmsize of the children if they
72 * have an own mm. This prevents forking servers to flood the
73 * machine with an endless amount of children. In case a single
74 * child is eating the vast majority of memory, adding only half
75 * to the parents will make the child our kill candidate of choice.
77 list_for_each_entry(child, &p->children, sibling) {
79 if (child->mm != mm && child->mm)
80 points += child->mm->total_vm/2 + 1;
85 * CPU time is in tens of seconds and run time is in thousands
86 * of seconds. There is no particular reason for this other than
87 * that it turned out to work very well in practice.
89 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
92 if (uptime >= p->start_time.tv_sec)
93 run_time = (uptime - p->start_time.tv_sec) >> 10;
97 s = int_sqrt(cpu_time);
100 s = int_sqrt(int_sqrt(run_time));
105 * Niced processes are most likely less important, so double
106 * their badness points.
108 if (task_nice(p) > 0)
112 * Superuser processes are usually more important, so we make it
113 * less likely that we kill those.
115 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
116 p->uid == 0 || p->euid == 0)
120 * We don't want to kill a process with direct hardware access.
121 * Not only could that mess up the hardware, but usually users
122 * tend to only have this flag set on applications they think
125 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
129 * Adjust the score by oomkilladj.
132 if (p->oomkilladj > 0)
133 points <<= p->oomkilladj;
135 points >>= -(p->oomkilladj);
139 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
140 p->pid, p->comm, points);
146 * Types of limitations to the nodes from which allocations may occur
148 #define CONSTRAINT_NONE 1
149 #define CONSTRAINT_MEMORY_POLICY 2
150 #define CONSTRAINT_CPUSET 3
153 * Determine the type of allocation constraint.
155 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
159 nodemask_t nodes = node_online_map;
161 for (z = zonelist->zones; *z; z++)
162 if (cpuset_zone_allowed(*z, gfp_mask))
163 node_clear((*z)->zone_pgdat->node_id,
166 return CONSTRAINT_CPUSET;
168 if (!nodes_empty(nodes))
169 return CONSTRAINT_MEMORY_POLICY;
172 return CONSTRAINT_NONE;
176 * Simple selection loop. We chose the process with the highest
177 * number of 'points'. We expect the caller will lock the tasklist.
179 * (not docbooked, we don't want this one cluttering up the manual)
181 static struct task_struct *select_bad_process(unsigned long *ppoints)
183 struct task_struct *g, *p;
184 struct task_struct *chosen = NULL;
185 struct timespec uptime;
188 do_posix_clock_monotonic_gettime(&uptime);
189 do_each_thread(g, p) {
190 unsigned long points;
193 /* skip the init task with pid == 1 */
196 if (p->oomkilladj == OOM_DISABLE)
198 /* If p's nodes don't overlap ours, it won't help to kill p. */
199 if (!cpuset_excl_nodes_overlap(p))
203 * This is in the process of releasing memory so for wait it
204 * to finish before killing some other task by mistake.
206 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
207 p->flags & PF_EXITING;
208 if (releasing && !(p->flags & PF_DEAD))
209 return ERR_PTR(-1UL);
210 if (p->flags & PF_SWAPOFF)
213 points = badness(p, uptime.tv_sec);
214 if (points > *ppoints || !chosen) {
218 } while_each_thread(g, p);
223 * We must be careful though to never send SIGKILL a process with
224 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
225 * we select a process with CAP_SYS_RAW_IO set).
227 static void __oom_kill_task(task_t *p, const char *message)
231 printk(KERN_WARNING "tried to kill init!\n");
236 if (!p->mm || p->mm == &init_mm) {
238 printk(KERN_WARNING "tried to kill an mm-less task!\n");
243 printk(KERN_ERR "%s: Killed process %d (%s).\n",
244 message, p->pid, p->comm);
247 * We give our sacrificial lamb high priority and access to
248 * all the memory it needs. That way it should be able to
249 * exit() and clear out its resources quickly...
252 set_tsk_thread_flag(p, TIF_MEMDIE);
254 force_sig(SIGKILL, p);
257 static int oom_kill_task(task_t *p, const char *message)
259 struct mm_struct *mm;
264 /* WARNING: mm may not be dereferenced since we did not obtain its
265 * value from get_task_mm(p). This is OK since all we need to do is
266 * compare mm to q->mm below.
268 * Furthermore, even if mm contains a non-NULL value, p->mm may
269 * change to NULL at any time since we do not hold task_lock(p).
270 * However, this is of no concern to us.
273 if (mm == NULL || mm == &init_mm)
276 __oom_kill_task(p, message);
278 * kill all processes that share the ->mm (i.e. all threads),
279 * but are in a different thread group
282 if (q->mm == mm && q->tgid != p->tgid)
283 __oom_kill_task(q, message);
284 while_each_thread(g, q);
289 static int oom_kill_process(struct task_struct *p, unsigned long points,
292 struct task_struct *c;
293 struct list_head *tsk;
295 printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li and "
296 "children.\n", p->pid, p->comm, points);
297 /* Try to kill a child first */
298 list_for_each(tsk, &p->children) {
299 c = list_entry(tsk, struct task_struct, sibling);
302 if (!oom_kill_task(c, message))
305 return oom_kill_task(p, message);
309 * oom_kill - kill the "best" process when we run out of memory
311 * If we run out of memory, we have the choice between either
312 * killing a random task (bad), letting the system crash (worse)
313 * OR try to be smart about which process to kill. Note that we
314 * don't have to be perfect here, we just have to be good.
316 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
319 unsigned long points = 0;
321 if (printk_ratelimit()) {
322 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
329 read_lock(&tasklist_lock);
332 * Check if there were limitations on the allocation (only relevant for
333 * NUMA) that may require different handling.
335 switch (constrained_alloc(zonelist, gfp_mask)) {
336 case CONSTRAINT_MEMORY_POLICY:
337 oom_kill_process(current, points,
338 "No available memory (MPOL_BIND)");
341 case CONSTRAINT_CPUSET:
342 oom_kill_process(current, points,
343 "No available memory in cpuset");
346 case CONSTRAINT_NONE:
349 * Rambo mode: Shoot down a process and hope it solves whatever
350 * issues we may have.
352 p = select_bad_process(&points);
354 if (PTR_ERR(p) == -1UL)
357 /* Found nothing?!?! Either we hang forever, or we panic. */
359 read_unlock(&tasklist_lock);
361 panic("Out of memory and no killable processes...\n");
364 if (oom_kill_process(p, points, "Out of memory"))
371 read_unlock(&tasklist_lock);
375 * Give "p" a good chance of killing itself before we
376 * retry to allocate memory unless "p" is current
378 if (!test_thread_flag(TIF_MEMDIE))
379 schedule_timeout_uninterruptible(1);