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 kswapd()
10 * in linux/mm/vmscan.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/swapctl.h>
22 #include <linux/timex.h>
23
24 /* #define DEBUG */
25
26 /**
27 * int_sqrt - oom_kill.c internal function, rough approximation to sqrt
28 * @x: integer of which to calculate the sqrt
29 *
30 * A very rough approximation to the sqrt() function.
31 */
32 static unsigned int int_sqrt(unsigned int x)
33 {
34 unsigned int out = x;
35 while (x & ~(unsigned int)1) x >>=2, out >>=1;
36 if (x) out -= out >> 2;
37 return (out ? out : 1);
38 }
39
40 /**
41 * oom_badness - calculate a numeric value for how bad this task has been
42 * @p: task struct of which task we should calculate
43 *
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.
47 *
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)
56 */
57
58 static int badness(struct task_struct *p)
59 {
60 int points, cpu_time, run_time;
61
62 if (!p->mm)
63 return 0;
64 /*
65 * The memory size of the process is the basis for the badness.
66 */
67 points = p->mm->total_vm;
68
69 /*
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...
74 */
75 cpu_time = (p->times.tms_utime + p->times.tms_stime) >> (SHIFT_HZ + 3);
76 run_time = (jiffies - p->start_time) >> (SHIFT_HZ + 10);
77
78 points /= int_sqrt(cpu_time);
79 points /= int_sqrt(int_sqrt(run_time));
80
81 /*
82 * Niced processes are most likely less important, so double
83 * their badness points.
84 */
85 if (p->nice > 0)
86 points *= 2;
87
88 /*
89 * Superuser processes are usually more important, so we make it
90 * less likely that we kill those.
91 */
92 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
93 p->uid == 0 || p->euid == 0)
94 points /= 4;
95
96 /*
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
100 * of as important.
101 */
102 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
103 points /= 4;
104 #ifdef DEBUG
105 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
106 p->pid, p->comm, points);
107 #endif
108 return points;
109 }
110
111 /*
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.
115 *
116 * (not docbooked, we don't want this one cluttering up the manual)
117 */
118 static struct task_struct * select_bad_process(void)
119 {
120 int maxpoints = 0;
121 struct task_struct *p = NULL;
122 struct task_struct *chosen = NULL;
123
124 read_lock(&tasklist_lock);
125 for_each_task(p) {
126 if (p->pid) {
127 int points = badness(p);
128 if (points > maxpoints) {
129 chosen = p;
130 maxpoints = points;
131 }
132 }
133 }
134 read_unlock(&tasklist_lock);
135 return chosen;
136 }
137
138 /**
139 * oom_kill - kill the "best" process when we run out of memory
140 *
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.
145 *
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).
149 */
150 void oom_kill(void)
151 {
152
153 struct task_struct *p = select_bad_process();
154
155 /* Found nothing?!?! Either we hang forever, or we panic. */
156 if (p == NULL)
157 panic("Out of memory and no killable processes...\n");
158
159 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", p->pid, p->comm);
160
161 /*
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...
165 */
166 p->counter = 5 * HZ;
167 p->flags |= PF_MEMALLOC;
168
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);
172 } else {
173 force_sig(SIGKILL, p);
174 }
175
176 /*
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
179 * for more memory.
180 */
181 current->policy |= SCHED_YIELD;
182 schedule();
183 return;
184 }
185
186 /**
187 * out_of_memory - is the system out of memory?
188 *
189 * Returns 0 if there is still enough memory left,
190 * 1 when we are out of memory (otherwise).
191 */
192 int out_of_memory(void)
193 {
194 struct sysinfo swp_info;
195
196 /* Enough free memory? Not OOM. */
197 if (nr_free_pages() > freepages.min)
198 return 0;
199
200 if (nr_free_pages() + nr_inactive_clean_pages() > freepages.low)
201 return 0;
202
203 /* Enough swap space left? Not OOM. */
204 si_swapinfo(&swp_info);
205 if (swp_info.freeswap > 0)
206 return 0;
207
208 /* Else... */
209 return 1;
210 }
211
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