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/oom.h> 19 #include <linux/mm.h> 20 #include <linux/sched.h> 21 #include <linux/swap.h> 22 #include <linux/timex.h> 23 #include <linux/jiffies.h> 24 #include <linux/cpuset.h> 25 #include <linux/module.h> 26 #include <linux/notifier.h> 27 28 int sysctl_panic_on_oom; 29 /* #define DEBUG */ 30 31 /** 32 * badness - calculate a numeric value for how bad this task has been 33 * @p: task struct of which task we should calculate 34 * @uptime: current uptime in seconds 35 * 36 * The formula used is relatively simple and documented inline in the 37 * function. The main rationale is that we want to select a good task 38 * to kill when we run out of memory. 39 * 40 * Good in this context means that: 41 * 1) we lose the minimum amount of work done 42 * 2) we recover a large amount of memory 43 * 3) we don't kill anything innocent of eating tons of memory 44 * 4) we want to kill the minimum amount of processes (one) 45 * 5) we try to kill the process the user expects us to kill, this 46 * algorithm has been meticulously tuned to meet the principle 47 * of least surprise ... (be careful when you change it) 48 */ 49 50 unsigned long badness(struct task_struct *p, unsigned long uptime) 51 { 52 unsigned long points, cpu_time, run_time, s; 53 struct mm_struct *mm; 54 struct task_struct *child; 55 56 task_lock(p); 57 mm = p->mm; 58 if (!mm) { 59 task_unlock(p); 60 return 0; 61 } 62 63 /* 64 * swapoff can easily use up all memory, so kill those first. 65 */ 66 if (p->flags & PF_SWAPOFF) 67 return ULONG_MAX; 68 69 /* 70 * The memory size of the process is the basis for the badness. 71 */ 72 points = mm->total_vm; 73 74 /* 75 * After this unlock we can no longer dereference local variable `mm' 76 */ 77 task_unlock(p); 78 79 /* 80 * Processes which fork a lot of child processes are likely 81 * a good choice. We add half the vmsize of the children if they 82 * have an own mm. This prevents forking servers to flood the 83 * machine with an endless amount of children. In case a single 84 * child is eating the vast majority of memory, adding only half 85 * to the parents will make the child our kill candidate of choice. 86 */ 87 list_for_each_entry(child, &p->children, sibling) { 88 task_lock(child); 89 if (child->mm != mm && child->mm) 90 points += child->mm->total_vm/2 + 1; 91 task_unlock(child); 92 } 93 94 /* 95 * CPU time is in tens of seconds and run time is in thousands 96 * of seconds. There is no particular reason for this other than 97 * that it turned out to work very well in practice. 98 */ 99 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 100 >> (SHIFT_HZ + 3); 101 102 if (uptime >= p->start_time.tv_sec) 103 run_time = (uptime - p->start_time.tv_sec) >> 10; 104 else 105 run_time = 0; 106 107 s = int_sqrt(cpu_time); 108 if (s) 109 points /= s; 110 s = int_sqrt(int_sqrt(run_time)); 111 if (s) 112 points /= s; 113 114 /* 115 * Niced processes are most likely less important, so double 116 * their badness points. 117 */ 118 if (task_nice(p) > 0) 119 points *= 2; 120 121 /* 122 * Superuser processes are usually more important, so we make it 123 * less likely that we kill those. 124 */ 125 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 126 p->uid == 0 || p->euid == 0) 127 points /= 4; 128 129 /* 130 * We don't want to kill a process with direct hardware access. 131 * Not only could that mess up the hardware, but usually users 132 * tend to only have this flag set on applications they think 133 * of as important. 134 */ 135 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 136 points /= 4; 137 138 /* 139 * If p's nodes don't overlap ours, it may still help to kill p 140 * because p may have allocated or otherwise mapped memory on 141 * this node before. However it will be less likely. 142 */ 143 if (!cpuset_excl_nodes_overlap(p)) 144 points /= 8; 145 146 /* 147 * Adjust the score by oomkilladj. 148 */ 149 if (p->oomkilladj) { 150 if (p->oomkilladj > 0) 151 points <<= p->oomkilladj; 152 else 153 points >>= -(p->oomkilladj); 154 } 155 156 #ifdef DEBUG 157 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 158 p->pid, p->comm, points); 159 #endif 160 return points; 161 } 162 163 /* 164 * Types of limitations to the nodes from which allocations may occur 165 */ 166 #define CONSTRAINT_NONE 1 167 #define CONSTRAINT_MEMORY_POLICY 2 168 #define CONSTRAINT_CPUSET 3 169 170 /* 171 * Determine the type of allocation constraint. 172 */ 173 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 174 { 175 #ifdef CONFIG_NUMA 176 struct zone **z; 177 nodemask_t nodes = node_online_map; 178 179 for (z = zonelist->zones; *z; z++) 180 if (cpuset_zone_allowed(*z, gfp_mask)) 181 node_clear(zone_to_nid(*z), nodes); 182 else 183 return CONSTRAINT_CPUSET; 184 185 if (!nodes_empty(nodes)) 186 return CONSTRAINT_MEMORY_POLICY; 187 #endif 188 189 return CONSTRAINT_NONE; 190 } 191 192 /* 193 * Simple selection loop. We chose the process with the highest 194 * number of 'points'. We expect the caller will lock the tasklist. 195 * 196 * (not docbooked, we don't want this one cluttering up the manual) 197 */ 198 static struct task_struct *select_bad_process(unsigned long *ppoints) 199 { 200 struct task_struct *g, *p; 201 struct task_struct *chosen = NULL; 202 struct timespec uptime; 203 *ppoints = 0; 204 205 do_posix_clock_monotonic_gettime(&uptime); 206 do_each_thread(g, p) { 207 unsigned long points; 208 209 /* 210 * skip kernel threads and tasks which have already released 211 * their mm. 212 */ 213 if (!p->mm) 214 continue; 215 /* skip the init task */ 216 if (is_init(p)) 217 continue; 218 219 /* 220 * This task already has access to memory reserves and is 221 * being killed. Don't allow any other task access to the 222 * memory reserve. 223 * 224 * Note: this may have a chance of deadlock if it gets 225 * blocked waiting for another task which itself is waiting 226 * for memory. Is there a better alternative? 227 */ 228 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 229 return ERR_PTR(-1UL); 230 231 /* 232 * This is in the process of releasing memory so wait for it 233 * to finish before killing some other task by mistake. 234 * 235 * However, if p is the current task, we allow the 'kill' to 236 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 237 * which will allow it to gain access to memory reserves in 238 * the process of exiting and releasing its resources. 239 * Otherwise we could get an easy OOM deadlock. 240 */ 241 if (p->flags & PF_EXITING) { 242 if (p != current) 243 return ERR_PTR(-1UL); 244 245 chosen = p; 246 *ppoints = ULONG_MAX; 247 } 248 249 if (p->oomkilladj == OOM_DISABLE) 250 continue; 251 252 points = badness(p, uptime.tv_sec); 253 if (points > *ppoints || !chosen) { 254 chosen = p; 255 *ppoints = points; 256 } 257 } while_each_thread(g, p); 258 259 return chosen; 260 } 261 262 /** 263 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 264 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 265 * set. 266 */ 267 static void __oom_kill_task(struct task_struct *p, int verbose) 268 { 269 if (is_init(p)) { 270 WARN_ON(1); 271 printk(KERN_WARNING "tried to kill init!\n"); 272 return; 273 } 274 275 if (!p->mm) { 276 WARN_ON(1); 277 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 278 return; 279 } 280 281 if (verbose) 282 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm); 283 284 /* 285 * We give our sacrificial lamb high priority and access to 286 * all the memory it needs. That way it should be able to 287 * exit() and clear out its resources quickly... 288 */ 289 p->time_slice = HZ; 290 set_tsk_thread_flag(p, TIF_MEMDIE); 291 292 force_sig(SIGKILL, p); 293 } 294 295 static int oom_kill_task(struct task_struct *p) 296 { 297 struct mm_struct *mm; 298 struct task_struct *g, *q; 299 300 mm = p->mm; 301 302 /* WARNING: mm may not be dereferenced since we did not obtain its 303 * value from get_task_mm(p). This is OK since all we need to do is 304 * compare mm to q->mm below. 305 * 306 * Furthermore, even if mm contains a non-NULL value, p->mm may 307 * change to NULL at any time since we do not hold task_lock(p). 308 * However, this is of no concern to us. 309 */ 310 311 if (mm == NULL) 312 return 1; 313 314 /* 315 * Don't kill the process if any threads are set to OOM_DISABLE 316 */ 317 do_each_thread(g, q) { 318 if (q->mm == mm && p->oomkilladj == OOM_DISABLE) 319 return 1; 320 } while_each_thread(g, q); 321 322 __oom_kill_task(p, 1); 323 324 /* 325 * kill all processes that share the ->mm (i.e. all threads), 326 * but are in a different thread group. Don't let them have access 327 * to memory reserves though, otherwise we might deplete all memory. 328 */ 329 do_each_thread(g, q) { 330 if (q->mm == mm && q->tgid != p->tgid) 331 force_sig(SIGKILL, p); 332 } while_each_thread(g, q); 333 334 return 0; 335 } 336 337 static int oom_kill_process(struct task_struct *p, unsigned long points, 338 const char *message) 339 { 340 struct task_struct *c; 341 struct list_head *tsk; 342 343 /* 344 * If the task is already exiting, don't alarm the sysadmin or kill 345 * its children or threads, just set TIF_MEMDIE so it can die quickly 346 */ 347 if (p->flags & PF_EXITING) { 348 __oom_kill_task(p, 0); 349 return 0; 350 } 351 352 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n", 353 message, p->pid, p->comm, points); 354 355 /* Try to kill a child first */ 356 list_for_each(tsk, &p->children) { 357 c = list_entry(tsk, struct task_struct, sibling); 358 if (c->mm == p->mm) 359 continue; 360 if (!oom_kill_task(c)) 361 return 0; 362 } 363 return oom_kill_task(p); 364 } 365 366 static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 367 368 int register_oom_notifier(struct notifier_block *nb) 369 { 370 return blocking_notifier_chain_register(&oom_notify_list, nb); 371 } 372 EXPORT_SYMBOL_GPL(register_oom_notifier); 373 374 int unregister_oom_notifier(struct notifier_block *nb) 375 { 376 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 377 } 378 EXPORT_SYMBOL_GPL(unregister_oom_notifier); 379 380 /** 381 * out_of_memory - kill the "best" process when we run out of memory 382 * 383 * If we run out of memory, we have the choice between either 384 * killing a random task (bad), letting the system crash (worse) 385 * OR try to be smart about which process to kill. Note that we 386 * don't have to be perfect here, we just have to be good. 387 */ 388 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 389 { 390 struct task_struct *p; 391 unsigned long points = 0; 392 unsigned long freed = 0; 393 394 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 395 if (freed > 0) 396 /* Got some memory back in the last second. */ 397 return; 398 399 if (printk_ratelimit()) { 400 printk(KERN_WARNING "%s invoked oom-killer: " 401 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 402 current->comm, gfp_mask, order, current->oomkilladj); 403 dump_stack(); 404 show_mem(); 405 } 406 407 cpuset_lock(); 408 read_lock(&tasklist_lock); 409 410 /* 411 * Check if there were limitations on the allocation (only relevant for 412 * NUMA) that may require different handling. 413 */ 414 switch (constrained_alloc(zonelist, gfp_mask)) { 415 case CONSTRAINT_MEMORY_POLICY: 416 oom_kill_process(current, points, 417 "No available memory (MPOL_BIND)"); 418 break; 419 420 case CONSTRAINT_CPUSET: 421 oom_kill_process(current, points, 422 "No available memory in cpuset"); 423 break; 424 425 case CONSTRAINT_NONE: 426 if (sysctl_panic_on_oom) 427 panic("out of memory. panic_on_oom is selected\n"); 428 retry: 429 /* 430 * Rambo mode: Shoot down a process and hope it solves whatever 431 * issues we may have. 432 */ 433 p = select_bad_process(&points); 434 435 if (PTR_ERR(p) == -1UL) 436 goto out; 437 438 /* Found nothing?!?! Either we hang forever, or we panic. */ 439 if (!p) { 440 read_unlock(&tasklist_lock); 441 cpuset_unlock(); 442 panic("Out of memory and no killable processes...\n"); 443 } 444 445 if (oom_kill_process(p, points, "Out of memory")) 446 goto retry; 447 448 break; 449 } 450 451 out: 452 read_unlock(&tasklist_lock); 453 cpuset_unlock(); 454 455 /* 456 * Give "p" a good chance of killing itself before we 457 * retry to allocate memory unless "p" is current 458 */ 459 if (!test_thread_flag(TIF_MEMDIE)) 460 schedule_timeout_uninterruptible(1); 461 } 462