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 * int_sqrt - oom_kill.c internal function, rough approximation to sqrt
28 * @x: integer of which to calculate the sqrt
30 * A very rough approximation to the sqrt() function.
32 static unsigned int int_sqrt(unsigned int x
)
35 while (x
& ~(unsigned int)1) x
>>=2, out
>>=1;
36 if (x
) out
-= out
>> 2;
37 return (out
? out
: 1);
41 * oom_badness - calculate a numeric value for how bad this task has been
42 * @p: task struct of which task we should calculate
44 * The formula used is relatively simple and documented inline in the
45 * function. The main rationale is that we want to select a good task
46 * to kill when we run out of memory.
48 * Good in this context means that:
49 * 1) we lose the minimum amount of work done
50 * 2) we recover a large amount of memory
51 * 3) we don't kill anything innocent of eating tons of memory
52 * 4) we want to kill the minimum amount of processes (one)
53 * 5) we try to kill the process the user expects us to kill, this
54 * algorithm has been meticulously tuned to meet the principle
55 * of least surprise ... (be careful when you change it)
58 static int badness(struct task_struct
*p
)
60 int points
, cpu_time
, run_time
;
65 if (p
->flags
& PF_MEMDIE
)
68 * The memory size of the process is the basis for the badness.
70 points
= p
->mm
->total_vm
;
73 * CPU time is in seconds and run time is in minutes. There is no
74 * particular reason for this other than that it turned out to work
75 * very well in practice.
77 cpu_time
= (p
->utime
+ p
->stime
) >> (SHIFT_HZ
+ 3);
78 run_time
= (get_jiffies_64() - p
->start_time
) >> (SHIFT_HZ
+ 10);
80 points
/= int_sqrt(cpu_time
);
81 points
/= int_sqrt(int_sqrt(run_time
));
84 * Niced processes are most likely less important, so double
85 * their badness points.
91 * Superuser processes are usually more important, so we make it
92 * less likely that we kill those.
94 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_ADMIN
) ||
95 p
->uid
== 0 || p
->euid
== 0)
99 * We don't want to kill a process with direct hardware access.
100 * Not only could that mess up the hardware, but usually users
101 * tend to only have this flag set on applications they think
104 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
))
107 printk(KERN_DEBUG
"OOMkill: task %d (%s) got %d points\n",
108 p
->pid
, p
->comm
, points
);
114 * Simple selection loop. We chose the process with the highest
115 * number of 'points'. We expect the caller will lock the tasklist.
117 * (not docbooked, we don't want this one cluttering up the manual)
119 static struct task_struct
* select_bad_process(void)
122 struct task_struct
*g
, *p
;
123 struct task_struct
*chosen
= NULL
;
127 int points
= badness(p
);
128 if (points
> maxpoints
) {
132 if (p
->flags
& PF_SWAPOFF
)
135 while_each_thread(g
, p
);
140 * We must be careful though to never send SIGKILL a process with
141 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
142 * we select a process with CAP_SYS_RAW_IO set).
144 static void __oom_kill_task(task_t
*p
)
147 if (!p
->mm
|| p
->mm
== &init_mm
) {
149 printk(KERN_WARNING
"tried to kill an mm-less task!\n");
154 printk(KERN_ERR
"Out of Memory: Killed process %d (%s).\n", p
->pid
, p
->comm
);
157 * We give our sacrificial lamb high priority and access to
158 * all the memory it needs. That way it should be able to
159 * exit() and clear out its resources quickly...
162 p
->flags
|= PF_MEMALLOC
| PF_MEMDIE
;
164 /* This process has hardware access, be more careful. */
165 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
)) {
166 force_sig(SIGTERM
, p
);
168 force_sig(SIGKILL
, p
);
172 static struct mm_struct
*oom_kill_task(task_t
*p
)
174 struct mm_struct
*mm
= get_task_mm(p
);
175 if (!mm
|| mm
== &init_mm
)
183 * oom_kill - kill the "best" process when we run out of memory
185 * If we run out of memory, we have the choice between either
186 * killing a random task (bad), letting the system crash (worse)
187 * OR try to be smart about which process to kill. Note that we
188 * don't have to be perfect here, we just have to be good.
190 static void oom_kill(void)
192 struct mm_struct
*mm
;
193 struct task_struct
*g
, *p
, *q
;
195 read_lock(&tasklist_lock
);
197 p
= select_bad_process();
199 /* Found nothing?!?! Either we hang forever, or we panic. */
202 panic("Out of memory and no killable processes...\n");
205 mm
= oom_kill_task(p
);
209 * kill all processes that share the ->mm (i.e. all threads),
210 * but are in a different thread group
213 if (q
->mm
== mm
&& q
->tgid
!= p
->tgid
)
215 while_each_thread(g
, q
);
217 printk(KERN_INFO
"Fixed up OOM kill of mm-less task\n");
218 read_unlock(&tasklist_lock
);
222 * Make kswapd go out of the way, so "p" has a good chance of
223 * killing itself before someone else gets the chance to ask
231 * out_of_memory - is the system out of memory?
233 void out_of_memory(void)
236 * oom_lock protects out_of_memory()'s static variables.
237 * It's a global lock; this is not performance-critical.
239 static spinlock_t oom_lock
= SPIN_LOCK_UNLOCKED
;
240 static unsigned long first
, last
, count
, lastkill
;
241 unsigned long now
, since
;
244 * Enough swap space left? Not OOM.
246 if (nr_swap_pages
> 0)
249 spin_lock(&oom_lock
);
255 * If it's been a long time since last failure,
263 * If we haven't tried for at least one second,
264 * we're not really oom.
271 * If we have gotten only a few failures,
272 * we're not really oom.
278 * If we just killed a process, wait a while
279 * to give that task a chance to exit. This
280 * avoids killing multiple processes needlessly.
282 since
= now
- lastkill
;
287 * Ok, really out of memory. Kill something.
291 /* oom_kill() sleeps */
292 spin_unlock(&oom_lock
);
294 spin_lock(&oom_lock
);
298 * We dropped the lock above, so check to be sure the variable
299 * first only ever increases to prevent false OOM's.
301 if (time_after(now
, first
))
306 spin_unlock(&oom_lock
);