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 * The memory size of the process is the basis for the badness. 65 */ 66 points = mm->total_vm; 67 68 /* 69 * After this unlock we can no longer dereference local variable `mm' 70 */ 71 task_unlock(p); 72 73 /* 74 * swapoff can easily use up all memory, so kill those first. 75 */ 76 if (p->flags & PF_SWAPOFF) 77 return ULONG_MAX; 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 if (!points) 152 points = 1; 153 points <<= p->oomkilladj; 154 } else 155 points >>= -(p->oomkilladj); 156 } 157 158 #ifdef DEBUG 159 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 160 p->pid, p->comm, points); 161 #endif 162 return points; 163 } 164 165 /* 166 * Types of limitations to the nodes from which allocations may occur 167 */ 168 #define CONSTRAINT_NONE 1 169 #define CONSTRAINT_MEMORY_POLICY 2 170 #define CONSTRAINT_CPUSET 3 171 172 /* 173 * Determine the type of allocation constraint. 174 */ 175 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 176 { 177 #ifdef CONFIG_NUMA 178 struct zone **z; 179 nodemask_t nodes; 180 int node; 181 182 nodes_clear(nodes); 183 /* node has memory ? */ 184 for_each_online_node(node) 185 if (NODE_DATA(node)->node_present_pages) 186 node_set(node, nodes); 187 188 for (z = zonelist->zones; *z; z++) 189 if (cpuset_zone_allowed_softwall(*z, gfp_mask)) 190 node_clear(zone_to_nid(*z), nodes); 191 else 192 return CONSTRAINT_CPUSET; 193 194 if (!nodes_empty(nodes)) 195 return CONSTRAINT_MEMORY_POLICY; 196 #endif 197 198 return CONSTRAINT_NONE; 199 } 200 201 /* 202 * Simple selection loop. We chose the process with the highest 203 * number of 'points'. We expect the caller will lock the tasklist. 204 * 205 * (not docbooked, we don't want this one cluttering up the manual) 206 */ 207 static struct task_struct *select_bad_process(unsigned long *ppoints) 208 { 209 struct task_struct *g, *p; 210 struct task_struct *chosen = NULL; 211 struct timespec uptime; 212 *ppoints = 0; 213 214 do_posix_clock_monotonic_gettime(&uptime); 215 do_each_thread(g, p) { 216 unsigned long points; 217 218 /* 219 * skip kernel threads and tasks which have already released 220 * their mm. 221 */ 222 if (!p->mm) 223 continue; 224 /* skip the init task */ 225 if (is_init(p)) 226 continue; 227 228 /* 229 * This task already has access to memory reserves and is 230 * being killed. Don't allow any other task access to the 231 * memory reserve. 232 * 233 * Note: this may have a chance of deadlock if it gets 234 * blocked waiting for another task which itself is waiting 235 * for memory. Is there a better alternative? 236 */ 237 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 238 return ERR_PTR(-1UL); 239 240 /* 241 * This is in the process of releasing memory so wait for it 242 * to finish before killing some other task by mistake. 243 * 244 * However, if p is the current task, we allow the 'kill' to 245 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 246 * which will allow it to gain access to memory reserves in 247 * the process of exiting and releasing its resources. 248 * Otherwise we could get an easy OOM deadlock. 249 */ 250 if (p->flags & PF_EXITING) { 251 if (p != current) 252 return ERR_PTR(-1UL); 253 254 chosen = p; 255 *ppoints = ULONG_MAX; 256 } 257 258 if (p->oomkilladj == OOM_DISABLE) 259 continue; 260 261 points = badness(p, uptime.tv_sec); 262 if (points > *ppoints || !chosen) { 263 chosen = p; 264 *ppoints = points; 265 } 266 } while_each_thread(g, p); 267 268 return chosen; 269 } 270 271 /** 272 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 273 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 274 * set. 275 */ 276 static void __oom_kill_task(struct task_struct *p, int verbose) 277 { 278 if (is_init(p)) { 279 WARN_ON(1); 280 printk(KERN_WARNING "tried to kill init!\n"); 281 return; 282 } 283 284 if (!p->mm) { 285 WARN_ON(1); 286 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 287 return; 288 } 289 290 if (verbose) 291 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm); 292 293 /* 294 * We give our sacrificial lamb high priority and access to 295 * all the memory it needs. That way it should be able to 296 * exit() and clear out its resources quickly... 297 */ 298 p->time_slice = HZ; 299 set_tsk_thread_flag(p, TIF_MEMDIE); 300 301 force_sig(SIGKILL, p); 302 } 303 304 static int oom_kill_task(struct task_struct *p) 305 { 306 struct mm_struct *mm; 307 struct task_struct *g, *q; 308 309 mm = p->mm; 310 311 /* WARNING: mm may not be dereferenced since we did not obtain its 312 * value from get_task_mm(p). This is OK since all we need to do is 313 * compare mm to q->mm below. 314 * 315 * Furthermore, even if mm contains a non-NULL value, p->mm may 316 * change to NULL at any time since we do not hold task_lock(p). 317 * However, this is of no concern to us. 318 */ 319 320 if (mm == NULL) 321 return 1; 322 323 /* 324 * Don't kill the process if any threads are set to OOM_DISABLE 325 */ 326 do_each_thread(g, q) { 327 if (q->mm == mm && q->oomkilladj == OOM_DISABLE) 328 return 1; 329 } while_each_thread(g, q); 330 331 __oom_kill_task(p, 1); 332 333 /* 334 * kill all processes that share the ->mm (i.e. all threads), 335 * but are in a different thread group. Don't let them have access 336 * to memory reserves though, otherwise we might deplete all memory. 337 */ 338 do_each_thread(g, q) { 339 if (q->mm == mm && q->tgid != p->tgid) 340 force_sig(SIGKILL, q); 341 } while_each_thread(g, q); 342 343 return 0; 344 } 345 346 static int oom_kill_process(struct task_struct *p, unsigned long points, 347 const char *message) 348 { 349 struct task_struct *c; 350 struct list_head *tsk; 351 352 /* 353 * If the task is already exiting, don't alarm the sysadmin or kill 354 * its children or threads, just set TIF_MEMDIE so it can die quickly 355 */ 356 if (p->flags & PF_EXITING) { 357 __oom_kill_task(p, 0); 358 return 0; 359 } 360 361 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n", 362 message, p->pid, p->comm, points); 363 364 /* Try to kill a child first */ 365 list_for_each(tsk, &p->children) { 366 c = list_entry(tsk, struct task_struct, sibling); 367 if (c->mm == p->mm) 368 continue; 369 if (!oom_kill_task(c)) 370 return 0; 371 } 372 return oom_kill_task(p); 373 } 374 375 static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 376 377 int register_oom_notifier(struct notifier_block *nb) 378 { 379 return blocking_notifier_chain_register(&oom_notify_list, nb); 380 } 381 EXPORT_SYMBOL_GPL(register_oom_notifier); 382 383 int unregister_oom_notifier(struct notifier_block *nb) 384 { 385 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 386 } 387 EXPORT_SYMBOL_GPL(unregister_oom_notifier); 388 389 /** 390 * out_of_memory - kill the "best" process when we run out of memory 391 * 392 * If we run out of memory, we have the choice between either 393 * killing a random task (bad), letting the system crash (worse) 394 * OR try to be smart about which process to kill. Note that we 395 * don't have to be perfect here, we just have to be good. 396 */ 397 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 398 { 399 struct task_struct *p; 400 unsigned long points = 0; 401 unsigned long freed = 0; 402 int constraint; 403 404 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 405 if (freed > 0) 406 /* Got some memory back in the last second. */ 407 return; 408 409 if (printk_ratelimit()) { 410 printk(KERN_WARNING "%s invoked oom-killer: " 411 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 412 current->comm, gfp_mask, order, current->oomkilladj); 413 dump_stack(); 414 show_mem(); 415 } 416 417 if (sysctl_panic_on_oom == 2) 418 panic("out of memory. Compulsory panic_on_oom is selected.\n"); 419 420 /* 421 * Check if there were limitations on the allocation (only relevant for 422 * NUMA) that may require different handling. 423 */ 424 constraint = constrained_alloc(zonelist, gfp_mask); 425 cpuset_lock(); 426 read_lock(&tasklist_lock); 427 428 switch (constraint) { 429 case CONSTRAINT_MEMORY_POLICY: 430 oom_kill_process(current, points, 431 "No available memory (MPOL_BIND)"); 432 break; 433 434 case CONSTRAINT_CPUSET: 435 oom_kill_process(current, points, 436 "No available memory in cpuset"); 437 break; 438 439 case CONSTRAINT_NONE: 440 if (sysctl_panic_on_oom) 441 panic("out of memory. panic_on_oom is selected\n"); 442 retry: 443 /* 444 * Rambo mode: Shoot down a process and hope it solves whatever 445 * issues we may have. 446 */ 447 p = select_bad_process(&points); 448 449 if (PTR_ERR(p) == -1UL) 450 goto out; 451 452 /* Found nothing?!?! Either we hang forever, or we panic. */ 453 if (!p) { 454 read_unlock(&tasklist_lock); 455 cpuset_unlock(); 456 panic("Out of memory and no killable processes...\n"); 457 } 458 459 if (oom_kill_process(p, points, "Out of memory")) 460 goto retry; 461 462 break; 463 } 464 465 out: 466 read_unlock(&tasklist_lock); 467 cpuset_unlock(); 468 469 /* 470 * Give "p" a good chance of killing itself before we 471 * retry to allocate memory unless "p" is current 472 */ 473 if (!test_thread_flag(TIF_MEMDIE)) 474 schedule_timeout_uninterruptible(1); 475 } 476