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 __alloc_pages() 10 * in mm/page_alloc.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/timex.h> 22 #include <linux/jiffies.h> 23 #include <linux/cpuset.h> 24 25 /* #define DEBUG */ 26 27 /** 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 31 * 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. 35 * 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) 44 */ 45 46 unsigned long badness(struct task_struct *p, unsigned long uptime) 47 { 48 unsigned long points, cpu_time, run_time, s; 49 struct list_head *tsk; 50 51 if (!p->mm) 52 return 0; 53 54 /* 55 * The memory size of the process is the basis for the badness. 56 */ 57 points = p->mm->total_vm; 58 59 /* 60 * Processes which fork a lot of child processes are likely 61 * a good choice. We add the vmsize of the children if they 62 * have an own mm. This prevents forking servers to flood the 63 * machine with an endless amount of children 64 */ 65 list_for_each(tsk, &p->children) { 66 struct task_struct *chld; 67 chld = list_entry(tsk, struct task_struct, sibling); 68 if (chld->mm != p->mm && chld->mm) 69 points += chld->mm->total_vm; 70 } 71 72 /* 73 * CPU time is in tens of seconds and run time is in thousands 74 * of seconds. There is no particular reason for this other than 75 * that it turned out to work very well in practice. 76 */ 77 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 78 >> (SHIFT_HZ + 3); 79 80 if (uptime >= p->start_time.tv_sec) 81 run_time = (uptime - p->start_time.tv_sec) >> 10; 82 else 83 run_time = 0; 84 85 s = int_sqrt(cpu_time); 86 if (s) 87 points /= s; 88 s = int_sqrt(int_sqrt(run_time)); 89 if (s) 90 points /= s; 91 92 /* 93 * Niced processes are most likely less important, so double 94 * their badness points. 95 */ 96 if (task_nice(p) > 0) 97 points *= 2; 98 99 /* 100 * Superuser processes are usually more important, so we make it 101 * less likely that we kill those. 102 */ 103 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 104 p->uid == 0 || p->euid == 0) 105 points /= 4; 106 107 /* 108 * We don't want to kill a process with direct hardware access. 109 * Not only could that mess up the hardware, but usually users 110 * tend to only have this flag set on applications they think 111 * of as important. 112 */ 113 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 114 points /= 4; 115 116 /* 117 * Adjust the score by oomkilladj. 118 */ 119 if (p->oomkilladj) { 120 if (p->oomkilladj > 0) 121 points <<= p->oomkilladj; 122 else 123 points >>= -(p->oomkilladj); 124 } 125 126 #ifdef DEBUG 127 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 128 p->pid, p->comm, points); 129 #endif 130 return points; 131 } 132 133 /* 134 * Simple selection loop. We chose the process with the highest 135 * number of 'points'. We expect the caller will lock the tasklist. 136 * 137 * (not docbooked, we don't want this one cluttering up the manual) 138 */ 139 static struct task_struct * select_bad_process(void) 140 { 141 unsigned long maxpoints = 0; 142 struct task_struct *g, *p; 143 struct task_struct *chosen = NULL; 144 struct timespec uptime; 145 146 do_posix_clock_monotonic_gettime(&uptime); 147 do_each_thread(g, p) { 148 unsigned long points; 149 int releasing; 150 151 /* skip the init task with pid == 1 */ 152 if (p->pid == 1) 153 continue; 154 if (p->oomkilladj == OOM_DISABLE) 155 continue; 156 /* If p's nodes don't overlap ours, it won't help to kill p. */ 157 if (!cpuset_excl_nodes_overlap(p)) 158 continue; 159 160 /* 161 * This is in the process of releasing memory so for wait it 162 * to finish before killing some other task by mistake. 163 */ 164 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) || 165 p->flags & PF_EXITING; 166 if (releasing && !(p->flags & PF_DEAD)) 167 return ERR_PTR(-1UL); 168 if (p->flags & PF_SWAPOFF) 169 return p; 170 171 points = badness(p, uptime.tv_sec); 172 if (points > maxpoints || !chosen) { 173 chosen = p; 174 maxpoints = points; 175 } 176 } while_each_thread(g, p); 177 return chosen; 178 } 179 180 /** 181 * We must be careful though to never send SIGKILL a process with 182 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that 183 * we select a process with CAP_SYS_RAW_IO set). 184 */ 185 static void __oom_kill_task(task_t *p) 186 { 187 if (p->pid == 1) { 188 WARN_ON(1); 189 printk(KERN_WARNING "tried to kill init!\n"); 190 return; 191 } 192 193 task_lock(p); 194 if (!p->mm || p->mm == &init_mm) { 195 WARN_ON(1); 196 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 197 task_unlock(p); 198 return; 199 } 200 task_unlock(p); 201 printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", 202 p->pid, p->comm); 203 204 /* 205 * We give our sacrificial lamb high priority and access to 206 * all the memory it needs. That way it should be able to 207 * exit() and clear out its resources quickly... 208 */ 209 p->time_slice = HZ; 210 set_tsk_thread_flag(p, TIF_MEMDIE); 211 212 force_sig(SIGKILL, p); 213 } 214 215 static struct mm_struct *oom_kill_task(task_t *p) 216 { 217 struct mm_struct *mm = get_task_mm(p); 218 task_t * g, * q; 219 220 if (!mm) 221 return NULL; 222 if (mm == &init_mm) { 223 mmput(mm); 224 return NULL; 225 } 226 227 __oom_kill_task(p); 228 /* 229 * kill all processes that share the ->mm (i.e. all threads), 230 * but are in a different thread group 231 */ 232 do_each_thread(g, q) 233 if (q->mm == mm && q->tgid != p->tgid) 234 __oom_kill_task(q); 235 while_each_thread(g, q); 236 237 return mm; 238 } 239 240 static struct mm_struct *oom_kill_process(struct task_struct *p) 241 { 242 struct mm_struct *mm; 243 struct task_struct *c; 244 struct list_head *tsk; 245 246 /* Try to kill a child first */ 247 list_for_each(tsk, &p->children) { 248 c = list_entry(tsk, struct task_struct, sibling); 249 if (c->mm == p->mm) 250 continue; 251 mm = oom_kill_task(c); 252 if (mm) 253 return mm; 254 } 255 return oom_kill_task(p); 256 } 257 258 /** 259 * oom_kill - kill the "best" process when we run out of memory 260 * 261 * If we run out of memory, we have the choice between either 262 * killing a random task (bad), letting the system crash (worse) 263 * OR try to be smart about which process to kill. Note that we 264 * don't have to be perfect here, we just have to be good. 265 */ 266 void out_of_memory(gfp_t gfp_mask, int order) 267 { 268 struct mm_struct *mm = NULL; 269 task_t * p; 270 271 if (printk_ratelimit()) { 272 printk("oom-killer: gfp_mask=0x%x, order=%d\n", 273 gfp_mask, order); 274 show_mem(); 275 } 276 277 read_lock(&tasklist_lock); 278 retry: 279 p = select_bad_process(); 280 281 if (PTR_ERR(p) == -1UL) 282 goto out; 283 284 /* Found nothing?!?! Either we hang forever, or we panic. */ 285 if (!p) { 286 read_unlock(&tasklist_lock); 287 panic("Out of memory and no killable processes...\n"); 288 } 289 290 mm = oom_kill_process(p); 291 if (!mm) 292 goto retry; 293 294 out: 295 read_unlock(&tasklist_lock); 296 if (mm) 297 mmput(mm); 298 299 /* 300 * Give "p" a good chance of killing itself before we 301 * retry to allocate memory. 302 */ 303 schedule_timeout_interruptible(1); 304 } 305