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 kswapd()
10 * in linux/mm/vmscan.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>
27 * oom_badness - calculate a numeric value for how bad this task has been
28 * @p: task struct of which task we should calculate
30 * The formula used is relatively simple and documented inline in the
31 * function. The main rationale is that we want to select a good task
32 * to kill when we run out of memory.
34 * Good in this context means that:
35 * 1) we lose the minimum amount of work done
36 * 2) we recover a large amount of memory
37 * 3) we don't kill anything innocent of eating tons of memory
38 * 4) we want to kill the minimum amount of processes (one)
39 * 5) we try to kill the process the user expects us to kill, this
40 * algorithm has been meticulously tuned to meet the principle
41 * of least surprise ... (be careful when you change it)
44 static int badness(struct task_struct *p)
46 int points, cpu_time, run_time, s;
51 if (p->flags & PF_MEMDIE)
54 * The memory size of the process is the basis for the badness.
56 points = p->mm->total_vm;
59 * CPU time is in seconds and run time is in minutes. There is no
60 * particular reason for this other than that it turned out to work
61 * very well in practice.
63 cpu_time = (p->utime + p->stime) >> (SHIFT_HZ + 3);
64 run_time = (get_jiffies_64() - p->start_time) >> (SHIFT_HZ + 10);
66 s = int_sqrt(cpu_time);
69 s = int_sqrt(int_sqrt(run_time));
74 * Niced processes are most likely less important, so double
75 * their badness points.
81 * Superuser processes are usually more important, so we make it
82 * less likely that we kill those.
84 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
85 p->uid == 0 || p->euid == 0)
89 * We don't want to kill a process with direct hardware access.
90 * Not only could that mess up the hardware, but usually users
91 * tend to only have this flag set on applications they think
94 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
97 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
98 p->pid, p->comm, points);
104 * Simple selection loop. We chose the process with the highest
105 * number of 'points'. We expect the caller will lock the tasklist.
107 * (not docbooked, we don't want this one cluttering up the manual)
109 static struct task_struct * select_bad_process(void)
112 struct task_struct *g, *p;
113 struct task_struct *chosen = NULL;
117 int points = badness(p);
118 if (points > maxpoints) {
122 if (p->flags & PF_SWAPOFF)
125 while_each_thread(g, p);
130 * We must be careful though to never send SIGKILL a process with
131 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
132 * we select a process with CAP_SYS_RAW_IO set).
134 static void __oom_kill_task(task_t *p)
137 if (!p->mm || p->mm == &init_mm) {
139 printk(KERN_WARNING "tried to kill an mm-less task!\n");
144 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", p->pid, p->comm);
147 * We give our sacrificial lamb high priority and access to
148 * all the memory it needs. That way it should be able to
149 * exit() and clear out its resources quickly...
152 p->flags |= PF_MEMALLOC | PF_MEMDIE;
154 /* This process has hardware access, be more careful. */
155 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) {
156 force_sig(SIGTERM, p);
158 force_sig(SIGKILL, p);
162 static struct mm_struct *oom_kill_task(task_t *p)
164 struct mm_struct *mm = get_task_mm(p);
165 if (!mm || mm == &init_mm)
173 * oom_kill - kill the "best" process when we run out of memory
175 * If we run out of memory, we have the choice between either
176 * killing a random task (bad), letting the system crash (worse)
177 * OR try to be smart about which process to kill. Note that we
178 * don't have to be perfect here, we just have to be good.
180 static void oom_kill(void)
182 struct mm_struct *mm;
183 struct task_struct *g, *p, *q;
185 read_lock(&tasklist_lock);
187 p = select_bad_process();
189 /* Found nothing?!?! Either we hang forever, or we panic. */
192 panic("Out of memory and no killable processes...\n");
195 mm = oom_kill_task(p);
199 * kill all processes that share the ->mm (i.e. all threads),
200 * but are in a different thread group
203 if (q->mm == mm && q->tgid != p->tgid)
205 while_each_thread(g, q);
207 printk(KERN_INFO "Fixed up OOM kill of mm-less task\n");
208 read_unlock(&tasklist_lock);
212 * Make kswapd go out of the way, so "p" has a good chance of
213 * killing itself before someone else gets the chance to ask
221 * out_of_memory - is the system out of memory?
223 void out_of_memory(int gfp_mask)
226 * oom_lock protects out_of_memory()'s static variables.
227 * It's a global lock; this is not performance-critical.
229 static spinlock_t oom_lock = SPIN_LOCK_UNLOCKED;
230 static unsigned long first, last, count, lastkill;
231 unsigned long now, since;
233 spin_lock(&oom_lock);
239 * If it's been a long time since last failure,
246 * If we haven't tried for at least one second,
247 * we're not really oom.
254 * If we have gotten only a few failures,
255 * we're not really oom.
261 * If we just killed a process, wait a while
262 * to give that task a chance to exit. This
263 * avoids killing multiple processes needlessly.
265 since = now - lastkill;
269 #if defined(CONFIG_MIPS_BRCM)
270 /* Killing processes on an embedded system won't help */
271 /* Print a warning message instead */
272 printk("Warning: Low memory condition - consider removing some software components\n");
275 * Ok, really out of memory. Kill something.
279 printk("oom-killer: gfp_mask=0x%x\n", gfp_mask);
282 /* oom_kill() sleeps */
283 spin_unlock(&oom_lock);
285 spin_lock(&oom_lock);
290 * We dropped the lock above, so check to be sure the variable
291 * first only ever increases to prevent false OOM's.
293 if (time_after(now, first))
298 spin_unlock(&oom_lock);