oom_kill.c revision f88ccad5886d5a864b8b0d48c666ee9998dec53f
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/gfp.h> 22#include <linux/sched.h> 23#include <linux/swap.h> 24#include <linux/timex.h> 25#include <linux/jiffies.h> 26#include <linux/cpuset.h> 27#include <linux/module.h> 28#include <linux/notifier.h> 29#include <linux/memcontrol.h> 30#include <linux/mempolicy.h> 31#include <linux/security.h> 32 33int sysctl_panic_on_oom; 34int sysctl_oom_kill_allocating_task; 35int sysctl_oom_dump_tasks = 1; 36static DEFINE_SPINLOCK(zone_scan_lock); 37/* #define DEBUG */ 38 39#ifdef CONFIG_NUMA 40/** 41 * has_intersects_mems_allowed() - check task eligiblity for kill 42 * @tsk: task struct of which task to consider 43 * @mask: nodemask passed to page allocator for mempolicy ooms 44 * 45 * Task eligibility is determined by whether or not a candidate task, @tsk, 46 * shares the same mempolicy nodes as current if it is bound by such a policy 47 * and whether or not it has the same set of allowed cpuset nodes. 48 */ 49static bool has_intersects_mems_allowed(struct task_struct *tsk, 50 const nodemask_t *mask) 51{ 52 struct task_struct *start = tsk; 53 54 do { 55 if (mask) { 56 /* 57 * If this is a mempolicy constrained oom, tsk's 58 * cpuset is irrelevant. Only return true if its 59 * mempolicy intersects current, otherwise it may be 60 * needlessly killed. 61 */ 62 if (mempolicy_nodemask_intersects(tsk, mask)) 63 return true; 64 } else { 65 /* 66 * This is not a mempolicy constrained oom, so only 67 * check the mems of tsk's cpuset. 68 */ 69 if (cpuset_mems_allowed_intersects(current, tsk)) 70 return true; 71 } 72 tsk = next_thread(tsk); 73 } while (tsk != start); 74 return false; 75} 76#else 77static bool has_intersects_mems_allowed(struct task_struct *tsk, 78 const nodemask_t *mask) 79{ 80 return true; 81} 82#endif /* CONFIG_NUMA */ 83 84/* 85 * The process p may have detached its own ->mm while exiting or through 86 * use_mm(), but one or more of its subthreads may still have a valid 87 * pointer. Return p, or any of its subthreads with a valid ->mm, with 88 * task_lock() held. 89 */ 90static struct task_struct *find_lock_task_mm(struct task_struct *p) 91{ 92 struct task_struct *t = p; 93 94 do { 95 task_lock(t); 96 if (likely(t->mm)) 97 return t; 98 task_unlock(t); 99 } while_each_thread(p, t); 100 101 return NULL; 102} 103 104/* return true if the task is not adequate as candidate victim task. */ 105static bool oom_unkillable_task(struct task_struct *p, struct mem_cgroup *mem, 106 const nodemask_t *nodemask) 107{ 108 if (is_global_init(p)) 109 return true; 110 if (p->flags & PF_KTHREAD) 111 return true; 112 113 /* When mem_cgroup_out_of_memory() and p is not member of the group */ 114 if (mem && !task_in_mem_cgroup(p, mem)) 115 return true; 116 117 /* p may not have freeable memory in nodemask */ 118 if (!has_intersects_mems_allowed(p, nodemask)) 119 return true; 120 121 return false; 122} 123 124/** 125 * badness - calculate a numeric value for how bad this task has been 126 * @p: task struct of which task we should calculate 127 * @uptime: current uptime in seconds 128 * 129 * The formula used is relatively simple and documented inline in the 130 * function. The main rationale is that we want to select a good task 131 * to kill when we run out of memory. 132 * 133 * Good in this context means that: 134 * 1) we lose the minimum amount of work done 135 * 2) we recover a large amount of memory 136 * 3) we don't kill anything innocent of eating tons of memory 137 * 4) we want to kill the minimum amount of processes (one) 138 * 5) we try to kill the process the user expects us to kill, this 139 * algorithm has been meticulously tuned to meet the principle 140 * of least surprise ... (be careful when you change it) 141 */ 142 143unsigned long badness(struct task_struct *p, unsigned long uptime) 144{ 145 unsigned long points, cpu_time, run_time; 146 struct task_struct *child; 147 struct task_struct *c, *t; 148 int oom_adj = p->signal->oom_adj; 149 struct task_cputime task_time; 150 unsigned long utime; 151 unsigned long stime; 152 153 if (oom_adj == OOM_DISABLE) 154 return 0; 155 156 p = find_lock_task_mm(p); 157 if (!p) 158 return 0; 159 160 /* 161 * The memory size of the process is the basis for the badness. 162 */ 163 points = p->mm->total_vm; 164 task_unlock(p); 165 166 /* 167 * swapoff can easily use up all memory, so kill those first. 168 */ 169 if (p->flags & PF_OOM_ORIGIN) 170 return ULONG_MAX; 171 172 /* 173 * Processes which fork a lot of child processes are likely 174 * a good choice. We add half the vmsize of the children if they 175 * have an own mm. This prevents forking servers to flood the 176 * machine with an endless amount of children. In case a single 177 * child is eating the vast majority of memory, adding only half 178 * to the parents will make the child our kill candidate of choice. 179 */ 180 t = p; 181 do { 182 list_for_each_entry(c, &t->children, sibling) { 183 child = find_lock_task_mm(c); 184 if (child) { 185 if (child->mm != p->mm) 186 points += child->mm->total_vm/2 + 1; 187 task_unlock(child); 188 } 189 } 190 } while_each_thread(p, t); 191 192 /* 193 * CPU time is in tens of seconds and run time is in thousands 194 * of seconds. There is no particular reason for this other than 195 * that it turned out to work very well in practice. 196 */ 197 thread_group_cputime(p, &task_time); 198 utime = cputime_to_jiffies(task_time.utime); 199 stime = cputime_to_jiffies(task_time.stime); 200 cpu_time = (utime + stime) >> (SHIFT_HZ + 3); 201 202 203 if (uptime >= p->start_time.tv_sec) 204 run_time = (uptime - p->start_time.tv_sec) >> 10; 205 else 206 run_time = 0; 207 208 if (cpu_time) 209 points /= int_sqrt(cpu_time); 210 if (run_time) 211 points /= int_sqrt(int_sqrt(run_time)); 212 213 /* 214 * Niced processes are most likely less important, so double 215 * their badness points. 216 */ 217 if (task_nice(p) > 0) 218 points *= 2; 219 220 /* 221 * Superuser processes are usually more important, so we make it 222 * less likely that we kill those. 223 */ 224 if (has_capability_noaudit(p, CAP_SYS_ADMIN) || 225 has_capability_noaudit(p, CAP_SYS_RESOURCE)) 226 points /= 4; 227 228 /* 229 * We don't want to kill a process with direct hardware access. 230 * Not only could that mess up the hardware, but usually users 231 * tend to only have this flag set on applications they think 232 * of as important. 233 */ 234 if (has_capability_noaudit(p, CAP_SYS_RAWIO)) 235 points /= 4; 236 237 /* 238 * Adjust the score by oom_adj. 239 */ 240 if (oom_adj) { 241 if (oom_adj > 0) { 242 if (!points) 243 points = 1; 244 points <<= oom_adj; 245 } else 246 points >>= -(oom_adj); 247 } 248 249#ifdef DEBUG 250 printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n", 251 p->pid, p->comm, points); 252#endif 253 return points; 254} 255 256/* 257 * Determine the type of allocation constraint. 258 */ 259#ifdef CONFIG_NUMA 260static enum oom_constraint constrained_alloc(struct zonelist *zonelist, 261 gfp_t gfp_mask, nodemask_t *nodemask) 262{ 263 struct zone *zone; 264 struct zoneref *z; 265 enum zone_type high_zoneidx = gfp_zone(gfp_mask); 266 267 /* 268 * Reach here only when __GFP_NOFAIL is used. So, we should avoid 269 * to kill current.We have to random task kill in this case. 270 * Hopefully, CONSTRAINT_THISNODE...but no way to handle it, now. 271 */ 272 if (gfp_mask & __GFP_THISNODE) 273 return CONSTRAINT_NONE; 274 275 /* 276 * The nodemask here is a nodemask passed to alloc_pages(). Now, 277 * cpuset doesn't use this nodemask for its hardwall/softwall/hierarchy 278 * feature. mempolicy is an only user of nodemask here. 279 * check mempolicy's nodemask contains all N_HIGH_MEMORY 280 */ 281 if (nodemask && !nodes_subset(node_states[N_HIGH_MEMORY], *nodemask)) 282 return CONSTRAINT_MEMORY_POLICY; 283 284 /* Check this allocation failure is caused by cpuset's wall function */ 285 for_each_zone_zonelist_nodemask(zone, z, zonelist, 286 high_zoneidx, nodemask) 287 if (!cpuset_zone_allowed_softwall(zone, gfp_mask)) 288 return CONSTRAINT_CPUSET; 289 290 return CONSTRAINT_NONE; 291} 292#else 293static enum oom_constraint constrained_alloc(struct zonelist *zonelist, 294 gfp_t gfp_mask, nodemask_t *nodemask) 295{ 296 return CONSTRAINT_NONE; 297} 298#endif 299 300/* 301 * Simple selection loop. We chose the process with the highest 302 * number of 'points'. We expect the caller will lock the tasklist. 303 * 304 * (not docbooked, we don't want this one cluttering up the manual) 305 */ 306static struct task_struct *select_bad_process(unsigned long *ppoints, 307 struct mem_cgroup *mem, const nodemask_t *nodemask) 308{ 309 struct task_struct *p; 310 struct task_struct *chosen = NULL; 311 struct timespec uptime; 312 *ppoints = 0; 313 314 do_posix_clock_monotonic_gettime(&uptime); 315 for_each_process(p) { 316 unsigned long points; 317 318 if (oom_unkillable_task(p, mem, nodemask)) 319 continue; 320 321 /* 322 * This task already has access to memory reserves and is 323 * being killed. Don't allow any other task access to the 324 * memory reserve. 325 * 326 * Note: this may have a chance of deadlock if it gets 327 * blocked waiting for another task which itself is waiting 328 * for memory. Is there a better alternative? 329 */ 330 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 331 return ERR_PTR(-1UL); 332 333 /* 334 * This is in the process of releasing memory so wait for it 335 * to finish before killing some other task by mistake. 336 * 337 * However, if p is the current task, we allow the 'kill' to 338 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 339 * which will allow it to gain access to memory reserves in 340 * the process of exiting and releasing its resources. 341 * Otherwise we could get an easy OOM deadlock. 342 */ 343 if ((p->flags & PF_EXITING) && p->mm) { 344 if (p != current) 345 return ERR_PTR(-1UL); 346 347 chosen = p; 348 *ppoints = ULONG_MAX; 349 } 350 351 if (p->signal->oom_adj == OOM_DISABLE) 352 continue; 353 354 points = badness(p, uptime.tv_sec); 355 if (points > *ppoints || !chosen) { 356 chosen = p; 357 *ppoints = points; 358 } 359 } 360 361 return chosen; 362} 363 364/** 365 * dump_tasks - dump current memory state of all system tasks 366 * @mem: current's memory controller, if constrained 367 * 368 * Dumps the current memory state of all system tasks, excluding kernel threads. 369 * State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj 370 * score, and name. 371 * 372 * If the actual is non-NULL, only tasks that are a member of the mem_cgroup are 373 * shown. 374 * 375 * Call with tasklist_lock read-locked. 376 */ 377static void dump_tasks(const struct mem_cgroup *mem) 378{ 379 struct task_struct *p; 380 struct task_struct *task; 381 382 printk(KERN_INFO "[ pid ] uid tgid total_vm rss cpu oom_adj " 383 "name\n"); 384 for_each_process(p) { 385 if (p->flags & PF_KTHREAD) 386 continue; 387 if (mem && !task_in_mem_cgroup(p, mem)) 388 continue; 389 390 task = find_lock_task_mm(p); 391 if (!task) { 392 /* 393 * This is a kthread or all of p's threads have already 394 * detached their mm's. There's no need to report 395 * them; they can't be oom killed anyway. 396 */ 397 continue; 398 } 399 400 printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3u %3d %s\n", 401 task->pid, __task_cred(task)->uid, task->tgid, 402 task->mm->total_vm, get_mm_rss(task->mm), 403 task_cpu(task), task->signal->oom_adj, task->comm); 404 task_unlock(task); 405 } 406} 407 408static void dump_header(struct task_struct *p, gfp_t gfp_mask, int order, 409 struct mem_cgroup *mem) 410{ 411 task_lock(current); 412 pr_warning("%s invoked oom-killer: gfp_mask=0x%x, order=%d, " 413 "oom_adj=%d\n", 414 current->comm, gfp_mask, order, current->signal->oom_adj); 415 cpuset_print_task_mems_allowed(current); 416 task_unlock(current); 417 dump_stack(); 418 mem_cgroup_print_oom_info(mem, p); 419 show_mem(); 420 if (sysctl_oom_dump_tasks) 421 dump_tasks(mem); 422} 423 424#define K(x) ((x) << (PAGE_SHIFT-10)) 425static int oom_kill_task(struct task_struct *p) 426{ 427 p = find_lock_task_mm(p); 428 if (!p || p->signal->oom_adj == OOM_DISABLE) { 429 task_unlock(p); 430 return 1; 431 } 432 pr_err("Killed process %d (%s) total-vm:%lukB, anon-rss:%lukB, file-rss:%lukB\n", 433 task_pid_nr(p), p->comm, K(p->mm->total_vm), 434 K(get_mm_counter(p->mm, MM_ANONPAGES)), 435 K(get_mm_counter(p->mm, MM_FILEPAGES))); 436 task_unlock(p); 437 438 p->rt.time_slice = HZ; 439 set_tsk_thread_flag(p, TIF_MEMDIE); 440 force_sig(SIGKILL, p); 441 return 0; 442} 443#undef K 444 445static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order, 446 unsigned long points, struct mem_cgroup *mem, 447 nodemask_t *nodemask, const char *message) 448{ 449 struct task_struct *victim = p; 450 struct task_struct *child; 451 struct task_struct *t = p; 452 unsigned long victim_points = 0; 453 struct timespec uptime; 454 455 if (printk_ratelimit()) 456 dump_header(p, gfp_mask, order, mem); 457 458 /* 459 * If the task is already exiting, don't alarm the sysadmin or kill 460 * its children or threads, just set TIF_MEMDIE so it can die quickly 461 */ 462 if (p->flags & PF_EXITING) { 463 set_tsk_thread_flag(p, TIF_MEMDIE); 464 return 0; 465 } 466 467 task_lock(p); 468 pr_err("%s: Kill process %d (%s) score %lu or sacrifice child\n", 469 message, task_pid_nr(p), p->comm, points); 470 task_unlock(p); 471 472 /* 473 * If any of p's children has a different mm and is eligible for kill, 474 * the one with the highest badness() score is sacrificed for its 475 * parent. This attempts to lose the minimal amount of work done while 476 * still freeing memory. 477 */ 478 do_posix_clock_monotonic_gettime(&uptime); 479 do { 480 list_for_each_entry(child, &t->children, sibling) { 481 unsigned long child_points; 482 483 if (child->mm == p->mm) 484 continue; 485 if (oom_unkillable_task(p, mem, nodemask)) 486 continue; 487 488 /* badness() returns 0 if the thread is unkillable */ 489 child_points = badness(child, uptime.tv_sec); 490 if (child_points > victim_points) { 491 victim = child; 492 victim_points = child_points; 493 } 494 } 495 } while_each_thread(p, t); 496 497 return oom_kill_task(victim); 498} 499 500/* 501 * Determines whether the kernel must panic because of the panic_on_oom sysctl. 502 */ 503static void check_panic_on_oom(enum oom_constraint constraint, gfp_t gfp_mask, 504 int order) 505{ 506 if (likely(!sysctl_panic_on_oom)) 507 return; 508 if (sysctl_panic_on_oom != 2) { 509 /* 510 * panic_on_oom == 1 only affects CONSTRAINT_NONE, the kernel 511 * does not panic for cpuset, mempolicy, or memcg allocation 512 * failures. 513 */ 514 if (constraint != CONSTRAINT_NONE) 515 return; 516 } 517 read_lock(&tasklist_lock); 518 dump_header(NULL, gfp_mask, order, NULL); 519 read_unlock(&tasklist_lock); 520 panic("Out of memory: %s panic_on_oom is enabled\n", 521 sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide"); 522} 523 524#ifdef CONFIG_CGROUP_MEM_RES_CTLR 525void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask) 526{ 527 unsigned long points = 0; 528 struct task_struct *p; 529 530 check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, 0); 531 read_lock(&tasklist_lock); 532retry: 533 p = select_bad_process(&points, mem, NULL); 534 if (!p || PTR_ERR(p) == -1UL) 535 goto out; 536 537 if (oom_kill_process(p, gfp_mask, 0, points, mem, NULL, 538 "Memory cgroup out of memory")) 539 goto retry; 540out: 541 read_unlock(&tasklist_lock); 542} 543#endif 544 545static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 546 547int register_oom_notifier(struct notifier_block *nb) 548{ 549 return blocking_notifier_chain_register(&oom_notify_list, nb); 550} 551EXPORT_SYMBOL_GPL(register_oom_notifier); 552 553int unregister_oom_notifier(struct notifier_block *nb) 554{ 555 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 556} 557EXPORT_SYMBOL_GPL(unregister_oom_notifier); 558 559/* 560 * Try to acquire the OOM killer lock for the zones in zonelist. Returns zero 561 * if a parallel OOM killing is already taking place that includes a zone in 562 * the zonelist. Otherwise, locks all zones in the zonelist and returns 1. 563 */ 564int try_set_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask) 565{ 566 struct zoneref *z; 567 struct zone *zone; 568 int ret = 1; 569 570 spin_lock(&zone_scan_lock); 571 for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) { 572 if (zone_is_oom_locked(zone)) { 573 ret = 0; 574 goto out; 575 } 576 } 577 578 for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) { 579 /* 580 * Lock each zone in the zonelist under zone_scan_lock so a 581 * parallel invocation of try_set_zonelist_oom() doesn't succeed 582 * when it shouldn't. 583 */ 584 zone_set_flag(zone, ZONE_OOM_LOCKED); 585 } 586 587out: 588 spin_unlock(&zone_scan_lock); 589 return ret; 590} 591 592/* 593 * Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed 594 * allocation attempts with zonelists containing them may now recall the OOM 595 * killer, if necessary. 596 */ 597void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask) 598{ 599 struct zoneref *z; 600 struct zone *zone; 601 602 spin_lock(&zone_scan_lock); 603 for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) { 604 zone_clear_flag(zone, ZONE_OOM_LOCKED); 605 } 606 spin_unlock(&zone_scan_lock); 607} 608 609/* 610 * Try to acquire the oom killer lock for all system zones. Returns zero if a 611 * parallel oom killing is taking place, otherwise locks all zones and returns 612 * non-zero. 613 */ 614static int try_set_system_oom(void) 615{ 616 struct zone *zone; 617 int ret = 1; 618 619 spin_lock(&zone_scan_lock); 620 for_each_populated_zone(zone) 621 if (zone_is_oom_locked(zone)) { 622 ret = 0; 623 goto out; 624 } 625 for_each_populated_zone(zone) 626 zone_set_flag(zone, ZONE_OOM_LOCKED); 627out: 628 spin_unlock(&zone_scan_lock); 629 return ret; 630} 631 632/* 633 * Clears ZONE_OOM_LOCKED for all system zones so that failed allocation 634 * attempts or page faults may now recall the oom killer, if necessary. 635 */ 636static void clear_system_oom(void) 637{ 638 struct zone *zone; 639 640 spin_lock(&zone_scan_lock); 641 for_each_populated_zone(zone) 642 zone_clear_flag(zone, ZONE_OOM_LOCKED); 643 spin_unlock(&zone_scan_lock); 644} 645 646/** 647 * out_of_memory - kill the "best" process when we run out of memory 648 * @zonelist: zonelist pointer 649 * @gfp_mask: memory allocation flags 650 * @order: amount of memory being requested as a power of 2 651 * @nodemask: nodemask passed to page allocator 652 * 653 * If we run out of memory, we have the choice between either 654 * killing a random task (bad), letting the system crash (worse) 655 * OR try to be smart about which process to kill. Note that we 656 * don't have to be perfect here, we just have to be good. 657 */ 658void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, 659 int order, nodemask_t *nodemask) 660{ 661 struct task_struct *p; 662 unsigned long freed = 0; 663 unsigned long points; 664 enum oom_constraint constraint = CONSTRAINT_NONE; 665 666 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 667 if (freed > 0) 668 /* Got some memory back in the last second. */ 669 return; 670 671 /* 672 * If current has a pending SIGKILL, then automatically select it. The 673 * goal is to allow it to allocate so that it may quickly exit and free 674 * its memory. 675 */ 676 if (fatal_signal_pending(current)) { 677 set_thread_flag(TIF_MEMDIE); 678 return; 679 } 680 681 /* 682 * Check if there were limitations on the allocation (only relevant for 683 * NUMA) that may require different handling. 684 */ 685 if (zonelist) 686 constraint = constrained_alloc(zonelist, gfp_mask, nodemask); 687 check_panic_on_oom(constraint, gfp_mask, order); 688 689 read_lock(&tasklist_lock); 690 if (sysctl_oom_kill_allocating_task && 691 !oom_unkillable_task(current, NULL, nodemask)) { 692 /* 693 * oom_kill_process() needs tasklist_lock held. If it returns 694 * non-zero, current could not be killed so we must fallback to 695 * the tasklist scan. 696 */ 697 if (!oom_kill_process(current, gfp_mask, order, 0, NULL, 698 nodemask, 699 "Out of memory (oom_kill_allocating_task)")) 700 return; 701 } 702 703retry: 704 p = select_bad_process(&points, NULL, 705 constraint == CONSTRAINT_MEMORY_POLICY ? nodemask : 706 NULL); 707 if (PTR_ERR(p) == -1UL) 708 return; 709 710 /* Found nothing?!?! Either we hang forever, or we panic. */ 711 if (!p) { 712 dump_header(NULL, gfp_mask, order, NULL); 713 read_unlock(&tasklist_lock); 714 panic("Out of memory and no killable processes...\n"); 715 } 716 717 if (oom_kill_process(p, gfp_mask, order, points, NULL, nodemask, 718 "Out of memory")) 719 goto retry; 720 read_unlock(&tasklist_lock); 721 722 /* 723 * Give "p" a good chance of killing itself before we 724 * retry to allocate memory unless "p" is current 725 */ 726 if (!test_thread_flag(TIF_MEMDIE)) 727 schedule_timeout_uninterruptible(1); 728} 729 730/* 731 * The pagefault handler calls here because it is out of memory, so kill a 732 * memory-hogging task. If a populated zone has ZONE_OOM_LOCKED set, a parallel 733 * oom killing is already in progress so do nothing. If a task is found with 734 * TIF_MEMDIE set, it has been killed so do nothing and allow it to exit. 735 */ 736void pagefault_out_of_memory(void) 737{ 738 if (try_set_system_oom()) { 739 out_of_memory(NULL, 0, 0, NULL); 740 clear_system_oom(); 741 } 742 if (!test_thread_flag(TIF_MEMDIE)) 743 schedule_timeout_uninterruptible(1); 744} 745