oom_kill.c revision 4e950f6f0189f65f8bf069cf2272649ef418f5e4
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; 30/* #define DEBUG */ 31 32/** 33 * badness - calculate a numeric value for how bad this task has been 34 * @p: task struct of which task we should calculate 35 * @uptime: current uptime in seconds 36 * 37 * The formula used is relatively simple and documented inline in the 38 * function. The main rationale is that we want to select a good task 39 * to kill when we run out of memory. 40 * 41 * Good in this context means that: 42 * 1) we lose the minimum amount of work done 43 * 2) we recover a large amount of memory 44 * 3) we don't kill anything innocent of eating tons of memory 45 * 4) we want to kill the minimum amount of processes (one) 46 * 5) we try to kill the process the user expects us to kill, this 47 * algorithm has been meticulously tuned to meet the principle 48 * of least surprise ... (be careful when you change it) 49 */ 50 51unsigned long badness(struct task_struct *p, unsigned long uptime) 52{ 53 unsigned long points, cpu_time, run_time, s; 54 struct mm_struct *mm; 55 struct task_struct *child; 56 57 task_lock(p); 58 mm = p->mm; 59 if (!mm) { 60 task_unlock(p); 61 return 0; 62 } 63 64 /* 65 * The memory size of the process is the basis for the badness. 66 */ 67 points = mm->total_vm; 68 69 /* 70 * After this unlock we can no longer dereference local variable `mm' 71 */ 72 task_unlock(p); 73 74 /* 75 * swapoff can easily use up all memory, so kill those first. 76 */ 77 if (p->flags & PF_SWAPOFF) 78 return ULONG_MAX; 79 80 /* 81 * Processes which fork a lot of child processes are likely 82 * a good choice. We add half the vmsize of the children if they 83 * have an own mm. This prevents forking servers to flood the 84 * machine with an endless amount of children. In case a single 85 * child is eating the vast majority of memory, adding only half 86 * to the parents will make the child our kill candidate of choice. 87 */ 88 list_for_each_entry(child, &p->children, sibling) { 89 task_lock(child); 90 if (child->mm != mm && child->mm) 91 points += child->mm->total_vm/2 + 1; 92 task_unlock(child); 93 } 94 95 /* 96 * CPU time is in tens of seconds and run time is in thousands 97 * of seconds. There is no particular reason for this other than 98 * that it turned out to work very well in practice. 99 */ 100 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 101 >> (SHIFT_HZ + 3); 102 103 if (uptime >= p->start_time.tv_sec) 104 run_time = (uptime - p->start_time.tv_sec) >> 10; 105 else 106 run_time = 0; 107 108 s = int_sqrt(cpu_time); 109 if (s) 110 points /= s; 111 s = int_sqrt(int_sqrt(run_time)); 112 if (s) 113 points /= s; 114 115 /* 116 * Niced processes are most likely less important, so double 117 * their badness points. 118 */ 119 if (task_nice(p) > 0) 120 points *= 2; 121 122 /* 123 * Superuser processes are usually more important, so we make it 124 * less likely that we kill those. 125 */ 126 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 127 p->uid == 0 || p->euid == 0) 128 points /= 4; 129 130 /* 131 * We don't want to kill a process with direct hardware access. 132 * Not only could that mess up the hardware, but usually users 133 * tend to only have this flag set on applications they think 134 * of as important. 135 */ 136 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 137 points /= 4; 138 139 /* 140 * If p's nodes don't overlap ours, it may still help to kill p 141 * because p may have allocated or otherwise mapped memory on 142 * this node before. However it will be less likely. 143 */ 144 if (!cpuset_excl_nodes_overlap(p)) 145 points /= 8; 146 147 /* 148 * Adjust the score by oomkilladj. 149 */ 150 if (p->oomkilladj) { 151 if (p->oomkilladj > 0) { 152 if (!points) 153 points = 1; 154 points <<= p->oomkilladj; 155 } else 156 points >>= -(p->oomkilladj); 157 } 158 159#ifdef DEBUG 160 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 161 p->pid, p->comm, points); 162#endif 163 return points; 164} 165 166/* 167 * Types of limitations to the nodes from which allocations may occur 168 */ 169#define CONSTRAINT_NONE 1 170#define CONSTRAINT_MEMORY_POLICY 2 171#define CONSTRAINT_CPUSET 3 172 173/* 174 * Determine the type of allocation constraint. 175 */ 176static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 177{ 178#ifdef CONFIG_NUMA 179 struct zone **z; 180 nodemask_t nodes; 181 int node; 182 183 nodes_clear(nodes); 184 /* node has memory ? */ 185 for_each_online_node(node) 186 if (NODE_DATA(node)->node_present_pages) 187 node_set(node, nodes); 188 189 for (z = zonelist->zones; *z; z++) 190 if (cpuset_zone_allowed_softwall(*z, gfp_mask)) 191 node_clear(zone_to_nid(*z), nodes); 192 else 193 return CONSTRAINT_CPUSET; 194 195 if (!nodes_empty(nodes)) 196 return CONSTRAINT_MEMORY_POLICY; 197#endif 198 199 return CONSTRAINT_NONE; 200} 201 202/* 203 * Simple selection loop. We chose the process with the highest 204 * number of 'points'. We expect the caller will lock the tasklist. 205 * 206 * (not docbooked, we don't want this one cluttering up the manual) 207 */ 208static struct task_struct *select_bad_process(unsigned long *ppoints) 209{ 210 struct task_struct *g, *p; 211 struct task_struct *chosen = NULL; 212 struct timespec uptime; 213 *ppoints = 0; 214 215 do_posix_clock_monotonic_gettime(&uptime); 216 do_each_thread(g, p) { 217 unsigned long points; 218 219 /* 220 * skip kernel threads and tasks which have already released 221 * their mm. 222 */ 223 if (!p->mm) 224 continue; 225 /* skip the init task */ 226 if (is_init(p)) 227 continue; 228 229 /* 230 * This task already has access to memory reserves and is 231 * being killed. Don't allow any other task access to the 232 * memory reserve. 233 * 234 * Note: this may have a chance of deadlock if it gets 235 * blocked waiting for another task which itself is waiting 236 * for memory. Is there a better alternative? 237 */ 238 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 239 return ERR_PTR(-1UL); 240 241 /* 242 * This is in the process of releasing memory so wait for it 243 * to finish before killing some other task by mistake. 244 * 245 * However, if p is the current task, we allow the 'kill' to 246 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 247 * which will allow it to gain access to memory reserves in 248 * the process of exiting and releasing its resources. 249 * Otherwise we could get an easy OOM deadlock. 250 */ 251 if (p->flags & PF_EXITING) { 252 if (p != current) 253 return ERR_PTR(-1UL); 254 255 chosen = p; 256 *ppoints = ULONG_MAX; 257 } 258 259 if (p->oomkilladj == OOM_DISABLE) 260 continue; 261 262 points = badness(p, uptime.tv_sec); 263 if (points > *ppoints || !chosen) { 264 chosen = p; 265 *ppoints = points; 266 } 267 } while_each_thread(g, p); 268 269 return chosen; 270} 271 272/** 273 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 274 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 275 * set. 276 */ 277static void __oom_kill_task(struct task_struct *p, int verbose) 278{ 279 if (is_init(p)) { 280 WARN_ON(1); 281 printk(KERN_WARNING "tried to kill init!\n"); 282 return; 283 } 284 285 if (!p->mm) { 286 WARN_ON(1); 287 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 288 return; 289 } 290 291 if (verbose) 292 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm); 293 294 /* 295 * We give our sacrificial lamb high priority and access to 296 * all the memory it needs. That way it should be able to 297 * exit() and clear out its resources quickly... 298 */ 299 p->time_slice = HZ; 300 set_tsk_thread_flag(p, TIF_MEMDIE); 301 302 force_sig(SIGKILL, p); 303} 304 305static int oom_kill_task(struct task_struct *p) 306{ 307 struct mm_struct *mm; 308 struct task_struct *g, *q; 309 310 mm = p->mm; 311 312 /* WARNING: mm may not be dereferenced since we did not obtain its 313 * value from get_task_mm(p). This is OK since all we need to do is 314 * compare mm to q->mm below. 315 * 316 * Furthermore, even if mm contains a non-NULL value, p->mm may 317 * change to NULL at any time since we do not hold task_lock(p). 318 * However, this is of no concern to us. 319 */ 320 321 if (mm == NULL) 322 return 1; 323 324 /* 325 * Don't kill the process if any threads are set to OOM_DISABLE 326 */ 327 do_each_thread(g, q) { 328 if (q->mm == mm && q->oomkilladj == OOM_DISABLE) 329 return 1; 330 } while_each_thread(g, q); 331 332 __oom_kill_task(p, 1); 333 334 /* 335 * kill all processes that share the ->mm (i.e. all threads), 336 * but are in a different thread group. Don't let them have access 337 * to memory reserves though, otherwise we might deplete all memory. 338 */ 339 do_each_thread(g, q) { 340 if (q->mm == mm && q->tgid != p->tgid) 341 force_sig(SIGKILL, q); 342 } while_each_thread(g, q); 343 344 return 0; 345} 346 347static int oom_kill_process(struct task_struct *p, unsigned long points, 348 const char *message) 349{ 350 struct task_struct *c; 351 struct list_head *tsk; 352 353 /* 354 * If the task is already exiting, don't alarm the sysadmin or kill 355 * its children or threads, just set TIF_MEMDIE so it can die quickly 356 */ 357 if (p->flags & PF_EXITING) { 358 __oom_kill_task(p, 0); 359 return 0; 360 } 361 362 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n", 363 message, p->pid, p->comm, points); 364 365 /* Try to kill a child first */ 366 list_for_each(tsk, &p->children) { 367 c = list_entry(tsk, struct task_struct, sibling); 368 if (c->mm == p->mm) 369 continue; 370 if (!oom_kill_task(c)) 371 return 0; 372 } 373 return oom_kill_task(p); 374} 375 376static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 377 378int register_oom_notifier(struct notifier_block *nb) 379{ 380 return blocking_notifier_chain_register(&oom_notify_list, nb); 381} 382EXPORT_SYMBOL_GPL(register_oom_notifier); 383 384int unregister_oom_notifier(struct notifier_block *nb) 385{ 386 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 387} 388EXPORT_SYMBOL_GPL(unregister_oom_notifier); 389 390/** 391 * out_of_memory - kill the "best" process when we run out of memory 392 * 393 * If we run out of memory, we have the choice between either 394 * killing a random task (bad), letting the system crash (worse) 395 * OR try to be smart about which process to kill. Note that we 396 * don't have to be perfect here, we just have to be good. 397 */ 398void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 399{ 400 struct task_struct *p; 401 unsigned long points = 0; 402 unsigned long freed = 0; 403 int constraint; 404 405 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 406 if (freed > 0) 407 /* Got some memory back in the last second. */ 408 return; 409 410 if (printk_ratelimit()) { 411 printk(KERN_WARNING "%s invoked oom-killer: " 412 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 413 current->comm, gfp_mask, order, current->oomkilladj); 414 dump_stack(); 415 show_mem(); 416 } 417 418 if (sysctl_panic_on_oom == 2) 419 panic("out of memory. Compulsory panic_on_oom is selected.\n"); 420 421 /* 422 * Check if there were limitations on the allocation (only relevant for 423 * NUMA) that may require different handling. 424 */ 425 constraint = constrained_alloc(zonelist, gfp_mask); 426 cpuset_lock(); 427 read_lock(&tasklist_lock); 428 429 switch (constraint) { 430 case CONSTRAINT_MEMORY_POLICY: 431 oom_kill_process(current, points, 432 "No available memory (MPOL_BIND)"); 433 break; 434 435 case CONSTRAINT_CPUSET: 436 oom_kill_process(current, points, 437 "No available memory in cpuset"); 438 break; 439 440 case CONSTRAINT_NONE: 441 if (sysctl_panic_on_oom) 442 panic("out of memory. panic_on_oom is selected\n"); 443retry: 444 /* 445 * Rambo mode: Shoot down a process and hope it solves whatever 446 * issues we may have. 447 */ 448 p = select_bad_process(&points); 449 450 if (PTR_ERR(p) == -1UL) 451 goto out; 452 453 /* Found nothing?!?! Either we hang forever, or we panic. */ 454 if (!p) { 455 read_unlock(&tasklist_lock); 456 cpuset_unlock(); 457 panic("Out of memory and no killable processes...\n"); 458 } 459 460 if (oom_kill_process(p, points, "Out of memory")) 461 goto retry; 462 463 break; 464 } 465 466out: 467 read_unlock(&tasklist_lock); 468 cpuset_unlock(); 469 470 /* 471 * Give "p" a good chance of killing itself before we 472 * retry to allocate memory unless "p" is current 473 */ 474 if (!test_thread_flag(TIF_MEMDIE)) 475 schedule_timeout_uninterruptible(1); 476} 477