oom_kill.c revision 098d7f128a4e53cb64930628915ac767785e0e60
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/err.h> 21#include <linux/sched.h> 22#include <linux/swap.h> 23#include <linux/timex.h> 24#include <linux/jiffies.h> 25#include <linux/cpuset.h> 26#include <linux/module.h> 27#include <linux/notifier.h> 28 29int sysctl_panic_on_oom; 30static DEFINE_MUTEX(zone_scan_mutex); 31/* #define DEBUG */ 32 33/** 34 * badness - calculate a numeric value for how bad this task has been 35 * @p: task struct of which task we should calculate 36 * @uptime: current uptime in seconds 37 * 38 * The formula used is relatively simple and documented inline in the 39 * function. The main rationale is that we want to select a good task 40 * to kill when we run out of memory. 41 * 42 * Good in this context means that: 43 * 1) we lose the minimum amount of work done 44 * 2) we recover a large amount of memory 45 * 3) we don't kill anything innocent of eating tons of memory 46 * 4) we want to kill the minimum amount of processes (one) 47 * 5) we try to kill the process the user expects us to kill, this 48 * algorithm has been meticulously tuned to meet the principle 49 * of least surprise ... (be careful when you change it) 50 */ 51 52unsigned long badness(struct task_struct *p, unsigned long uptime) 53{ 54 unsigned long points, cpu_time, run_time, s; 55 struct mm_struct *mm; 56 struct task_struct *child; 57 58 task_lock(p); 59 mm = p->mm; 60 if (!mm) { 61 task_unlock(p); 62 return 0; 63 } 64 65 /* 66 * The memory size of the process is the basis for the badness. 67 */ 68 points = mm->total_vm; 69 70 /* 71 * After this unlock we can no longer dereference local variable `mm' 72 */ 73 task_unlock(p); 74 75 /* 76 * swapoff can easily use up all memory, so kill those first. 77 */ 78 if (p->flags & PF_SWAPOFF) 79 return ULONG_MAX; 80 81 /* 82 * Processes which fork a lot of child processes are likely 83 * a good choice. We add half the vmsize of the children if they 84 * have an own mm. This prevents forking servers to flood the 85 * machine with an endless amount of children. In case a single 86 * child is eating the vast majority of memory, adding only half 87 * to the parents will make the child our kill candidate of choice. 88 */ 89 list_for_each_entry(child, &p->children, sibling) { 90 task_lock(child); 91 if (child->mm != mm && child->mm) 92 points += child->mm->total_vm/2 + 1; 93 task_unlock(child); 94 } 95 96 /* 97 * CPU time is in tens of seconds and run time is in thousands 98 * of seconds. There is no particular reason for this other than 99 * that it turned out to work very well in practice. 100 */ 101 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 102 >> (SHIFT_HZ + 3); 103 104 if (uptime >= p->start_time.tv_sec) 105 run_time = (uptime - p->start_time.tv_sec) >> 10; 106 else 107 run_time = 0; 108 109 s = int_sqrt(cpu_time); 110 if (s) 111 points /= s; 112 s = int_sqrt(int_sqrt(run_time)); 113 if (s) 114 points /= s; 115 116 /* 117 * Niced processes are most likely less important, so double 118 * their badness points. 119 */ 120 if (task_nice(p) > 0) 121 points *= 2; 122 123 /* 124 * Superuser processes are usually more important, so we make it 125 * less likely that we kill those. 126 */ 127 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 128 p->uid == 0 || p->euid == 0) 129 points /= 4; 130 131 /* 132 * We don't want to kill a process with direct hardware access. 133 * Not only could that mess up the hardware, but usually users 134 * tend to only have this flag set on applications they think 135 * of as important. 136 */ 137 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 138 points /= 4; 139 140 /* 141 * If p's nodes don't overlap ours, it may still help to kill p 142 * because p may have allocated or otherwise mapped memory on 143 * this node before. However it will be less likely. 144 */ 145 if (!cpuset_excl_nodes_overlap(p)) 146 points /= 8; 147 148 /* 149 * Adjust the score by oomkilladj. 150 */ 151 if (p->oomkilladj) { 152 if (p->oomkilladj > 0) { 153 if (!points) 154 points = 1; 155 points <<= p->oomkilladj; 156 } else 157 points >>= -(p->oomkilladj); 158 } 159 160#ifdef DEBUG 161 printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n", 162 p->pid, p->comm, points); 163#endif 164 return points; 165} 166 167/* 168 * Determine the type of allocation constraint. 169 */ 170static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist, 171 gfp_t gfp_mask) 172{ 173#ifdef CONFIG_NUMA 174 struct zone **z; 175 nodemask_t nodes = node_states[N_HIGH_MEMORY]; 176 177 for (z = zonelist->zones; *z; z++) 178 if (cpuset_zone_allowed_softwall(*z, gfp_mask)) 179 node_clear(zone_to_nid(*z), nodes); 180 else 181 return CONSTRAINT_CPUSET; 182 183 if (!nodes_empty(nodes)) 184 return CONSTRAINT_MEMORY_POLICY; 185#endif 186 187 return CONSTRAINT_NONE; 188} 189 190/* 191 * Simple selection loop. We chose the process with the highest 192 * number of 'points'. We expect the caller will lock the tasklist. 193 * 194 * (not docbooked, we don't want this one cluttering up the manual) 195 */ 196static struct task_struct *select_bad_process(unsigned long *ppoints) 197{ 198 struct task_struct *g, *p; 199 struct task_struct *chosen = NULL; 200 struct timespec uptime; 201 *ppoints = 0; 202 203 do_posix_clock_monotonic_gettime(&uptime); 204 do_each_thread(g, p) { 205 unsigned long points; 206 207 /* 208 * skip kernel threads and tasks which have already released 209 * their mm. 210 */ 211 if (!p->mm) 212 continue; 213 /* skip the init task */ 214 if (is_init(p)) 215 continue; 216 217 /* 218 * This task already has access to memory reserves and is 219 * being killed. Don't allow any other task access to the 220 * memory reserve. 221 * 222 * Note: this may have a chance of deadlock if it gets 223 * blocked waiting for another task which itself is waiting 224 * for memory. Is there a better alternative? 225 */ 226 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 227 return ERR_PTR(-1UL); 228 229 /* 230 * This is in the process of releasing memory so wait for it 231 * to finish before killing some other task by mistake. 232 * 233 * However, if p is the current task, we allow the 'kill' to 234 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 235 * which will allow it to gain access to memory reserves in 236 * the process of exiting and releasing its resources. 237 * Otherwise we could get an easy OOM deadlock. 238 */ 239 if (p->flags & PF_EXITING) { 240 if (p != current) 241 return ERR_PTR(-1UL); 242 243 chosen = p; 244 *ppoints = ULONG_MAX; 245 } 246 247 if (p->oomkilladj == OOM_DISABLE) 248 continue; 249 250 points = badness(p, uptime.tv_sec); 251 if (points > *ppoints || !chosen) { 252 chosen = p; 253 *ppoints = points; 254 } 255 } while_each_thread(g, p); 256 257 return chosen; 258} 259 260/** 261 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 262 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 263 * set. 264 */ 265static void __oom_kill_task(struct task_struct *p, int verbose) 266{ 267 if (is_init(p)) { 268 WARN_ON(1); 269 printk(KERN_WARNING "tried to kill init!\n"); 270 return; 271 } 272 273 if (!p->mm) { 274 WARN_ON(1); 275 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 276 return; 277 } 278 279 if (verbose) 280 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm); 281 282 /* 283 * We give our sacrificial lamb high priority and access to 284 * all the memory it needs. That way it should be able to 285 * exit() and clear out its resources quickly... 286 */ 287 p->time_slice = HZ; 288 set_tsk_thread_flag(p, TIF_MEMDIE); 289 290 force_sig(SIGKILL, p); 291} 292 293static int oom_kill_task(struct task_struct *p) 294{ 295 struct mm_struct *mm; 296 struct task_struct *g, *q; 297 298 mm = p->mm; 299 300 /* WARNING: mm may not be dereferenced since we did not obtain its 301 * value from get_task_mm(p). This is OK since all we need to do is 302 * compare mm to q->mm below. 303 * 304 * Furthermore, even if mm contains a non-NULL value, p->mm may 305 * change to NULL at any time since we do not hold task_lock(p). 306 * However, this is of no concern to us. 307 */ 308 309 if (mm == NULL) 310 return 1; 311 312 /* 313 * Don't kill the process if any threads are set to OOM_DISABLE 314 */ 315 do_each_thread(g, q) { 316 if (q->mm == mm && q->oomkilladj == OOM_DISABLE) 317 return 1; 318 } while_each_thread(g, q); 319 320 __oom_kill_task(p, 1); 321 322 /* 323 * kill all processes that share the ->mm (i.e. all threads), 324 * but are in a different thread group. Don't let them have access 325 * to memory reserves though, otherwise we might deplete all memory. 326 */ 327 do_each_thread(g, q) { 328 if (q->mm == mm && q->tgid != p->tgid) 329 force_sig(SIGKILL, q); 330 } while_each_thread(g, q); 331 332 return 0; 333} 334 335static int oom_kill_process(struct task_struct *p, unsigned long points, 336 const char *message) 337{ 338 struct task_struct *c; 339 struct list_head *tsk; 340 341 /* 342 * If the task is already exiting, don't alarm the sysadmin or kill 343 * its children or threads, just set TIF_MEMDIE so it can die quickly 344 */ 345 if (p->flags & PF_EXITING) { 346 __oom_kill_task(p, 0); 347 return 0; 348 } 349 350 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n", 351 message, p->pid, p->comm, points); 352 353 /* Try to kill a child first */ 354 list_for_each(tsk, &p->children) { 355 c = list_entry(tsk, struct task_struct, sibling); 356 if (c->mm == p->mm) 357 continue; 358 if (!oom_kill_task(c)) 359 return 0; 360 } 361 return oom_kill_task(p); 362} 363 364static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 365 366int register_oom_notifier(struct notifier_block *nb) 367{ 368 return blocking_notifier_chain_register(&oom_notify_list, nb); 369} 370EXPORT_SYMBOL_GPL(register_oom_notifier); 371 372int unregister_oom_notifier(struct notifier_block *nb) 373{ 374 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 375} 376EXPORT_SYMBOL_GPL(unregister_oom_notifier); 377 378/* 379 * Try to acquire the OOM killer lock for the zones in zonelist. Returns zero 380 * if a parallel OOM killing is already taking place that includes a zone in 381 * the zonelist. Otherwise, locks all zones in the zonelist and returns 1. 382 */ 383int try_set_zone_oom(struct zonelist *zonelist) 384{ 385 struct zone **z; 386 int ret = 1; 387 388 z = zonelist->zones; 389 390 mutex_lock(&zone_scan_mutex); 391 do { 392 if (zone_is_oom_locked(*z)) { 393 ret = 0; 394 goto out; 395 } 396 } while (*(++z) != NULL); 397 398 /* 399 * Lock each zone in the zonelist under zone_scan_mutex so a parallel 400 * invocation of try_set_zone_oom() doesn't succeed when it shouldn't. 401 */ 402 z = zonelist->zones; 403 do { 404 zone_set_flag(*z, ZONE_OOM_LOCKED); 405 } while (*(++z) != NULL); 406out: 407 mutex_unlock(&zone_scan_mutex); 408 return ret; 409} 410 411/* 412 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed 413 * allocation attempts with zonelists containing them may now recall the OOM 414 * killer, if necessary. 415 */ 416void clear_zonelist_oom(struct zonelist *zonelist) 417{ 418 struct zone **z; 419 420 z = zonelist->zones; 421 422 mutex_lock(&zone_scan_mutex); 423 do { 424 zone_clear_flag(*z, ZONE_OOM_LOCKED); 425 } while (*(++z) != NULL); 426 mutex_unlock(&zone_scan_mutex); 427} 428 429/** 430 * out_of_memory - kill the "best" process when we run out of memory 431 * 432 * If we run out of memory, we have the choice between either 433 * killing a random task (bad), letting the system crash (worse) 434 * OR try to be smart about which process to kill. Note that we 435 * don't have to be perfect here, we just have to be good. 436 */ 437void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 438{ 439 struct task_struct *p; 440 unsigned long points = 0; 441 unsigned long freed = 0; 442 enum oom_constraint constraint; 443 444 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 445 if (freed > 0) 446 /* Got some memory back in the last second. */ 447 return; 448 449 if (printk_ratelimit()) { 450 printk(KERN_WARNING "%s invoked oom-killer: " 451 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 452 current->comm, gfp_mask, order, current->oomkilladj); 453 dump_stack(); 454 show_mem(); 455 } 456 457 if (sysctl_panic_on_oom == 2) 458 panic("out of memory. Compulsory panic_on_oom is selected.\n"); 459 460 /* 461 * Check if there were limitations on the allocation (only relevant for 462 * NUMA) that may require different handling. 463 */ 464 constraint = constrained_alloc(zonelist, gfp_mask); 465 cpuset_lock(); 466 read_lock(&tasklist_lock); 467 468 switch (constraint) { 469 case CONSTRAINT_MEMORY_POLICY: 470 oom_kill_process(current, points, 471 "No available memory (MPOL_BIND)"); 472 break; 473 474 case CONSTRAINT_CPUSET: 475 oom_kill_process(current, points, 476 "No available memory in cpuset"); 477 break; 478 479 case CONSTRAINT_NONE: 480 if (sysctl_panic_on_oom) 481 panic("out of memory. panic_on_oom is selected\n"); 482retry: 483 /* 484 * Rambo mode: Shoot down a process and hope it solves whatever 485 * issues we may have. 486 */ 487 p = select_bad_process(&points); 488 489 if (PTR_ERR(p) == -1UL) 490 goto out; 491 492 /* Found nothing?!?! Either we hang forever, or we panic. */ 493 if (!p) { 494 read_unlock(&tasklist_lock); 495 cpuset_unlock(); 496 panic("Out of memory and no killable processes...\n"); 497 } 498 499 if (oom_kill_process(p, points, "Out of memory")) 500 goto retry; 501 502 break; 503 } 504 505out: 506 read_unlock(&tasklist_lock); 507 cpuset_unlock(); 508 509 /* 510 * Give "p" a good chance of killing itself before we 511 * retry to allocate memory unless "p" is current 512 */ 513 if (!test_thread_flag(TIF_MEMDIE)) 514 schedule_timeout_uninterruptible(1); 515} 516