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/swapctl.h>
22 #include <linux/timex.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 priniciple
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 * The memory size of the process is the basis for the badness.
67 points
= p
->mm
->total_vm
;
70 * CPU time is in seconds and run time is in minutes. There is no
71 * particular reason for this other than that it turned out to work
72 * very well in practice. This is not safe against jiffie wraps
73 * but we don't care _that_ much...
75 cpu_time
= (p
->times
.tms_utime
+ p
->times
.tms_stime
) >> (SHIFT_HZ
+ 3);
76 run_time
= (jiffies
- p
->start_time
) >> (SHIFT_HZ
+ 10);
78 points
/= int_sqrt(cpu_time
);
79 points
/= int_sqrt(int_sqrt(run_time
));
82 * Niced processes are most likely less important, so double
83 * their badness points.
89 * Superuser processes are usually more important, so we make it
90 * less likely that we kill those.
92 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_ADMIN
) ||
93 p
->uid
== 0 || p
->euid
== 0)
97 * We don't want to kill a process with direct hardware access.
98 * Not only could that mess up the hardware, but usually users
99 * tend to only have this flag set on applications they think
102 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
))
105 printk(KERN_DEBUG
"OOMkill: task %d (%s) got %d points\n",
106 p
->pid
, p
->comm
, points
);
112 * Simple selection loop. We chose the process with the highest
113 * number of 'points'. We need the locks to make sure that the
114 * list of task structs doesn't change while we look the other way.
116 * (not docbooked, we don't want this one cluttering up the manual)
118 static struct task_struct
* select_bad_process(void)
121 struct task_struct
*p
= NULL
;
122 struct task_struct
*chosen
= NULL
;
124 read_lock(&tasklist_lock
);
127 int points
= badness(p
);
128 if (points
> maxpoints
) {
134 read_unlock(&tasklist_lock
);
139 * oom_kill - kill the "best" process when we run out of memory
141 * If we run out of memory, we have the choice between either
142 * killing a random task (bad), letting the system crash (worse)
143 * OR try to be smart about which process to kill. Note that we
144 * don't have to be perfect here, we just have to be good.
146 * We must be careful though to never send SIGKILL a process with
147 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
148 * we select a process with CAP_SYS_RAW_IO set).
153 struct task_struct
*p
= select_bad_process();
155 /* Found nothing?!?! Either we hang forever, or we panic. */
157 panic("Out of memory and no killable processes...\n");
159 printk(KERN_ERR
"Out of Memory: Killed process %d (%s).\n", p
->pid
, p
->comm
);
162 * We give our sacrificial lamb high priority and access to
163 * all the memory it needs. That way it should be able to
164 * exit() and clear out its resources quickly...
167 p
->flags
|= PF_MEMALLOC
;
169 /* This process has hardware access, be more careful. */
170 if (cap_t(p
->cap_effective
) & CAP_TO_MASK(CAP_SYS_RAWIO
)) {
171 force_sig(SIGTERM
, p
);
173 force_sig(SIGKILL
, p
);
177 * Make kswapd go out of the way, so "p" has a good chance of
178 * killing itself before someone else gets the chance to ask
181 current
->policy
|= SCHED_YIELD
;
187 * out_of_memory - is the system out of memory?
189 * Returns 0 if there is still enough memory left,
190 * 1 when we are out of memory (otherwise).
192 int out_of_memory(void)
194 struct sysinfo swp_info
;
196 /* Enough free memory? Not OOM. */
197 if (nr_free_pages() > freepages
.min
)
200 if (nr_free_pages() + nr_inactive_clean_pages() > freepages
.low
)
203 /* Enough swap space left? Not OOM. */
204 si_swapinfo(&swp_info
);
205 if (swp_info
.freeswap
> 0)