oom_kill.c revision 35ae834fa02ba89cfbd4a80892c0e458fd6d5c0b
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 28int 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 50unsigned 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 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 */ 173static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 174{ 175#ifdef CONFIG_NUMA 176 struct zone **z; 177 nodemask_t nodes; 178 int node; 179 /* node has memory ? */ 180 for_each_online_node(node) 181 if (NODE_DATA(node)->node_present_pages) 182 node_set(node, nodes); 183 184 for (z = zonelist->zones; *z; z++) 185 if (cpuset_zone_allowed_softwall(*z, gfp_mask)) 186 node_clear(zone_to_nid(*z), nodes); 187 else 188 return CONSTRAINT_CPUSET; 189 190 if (!nodes_empty(nodes)) 191 return CONSTRAINT_MEMORY_POLICY; 192#endif 193 194 return CONSTRAINT_NONE; 195} 196 197/* 198 * Simple selection loop. We chose the process with the highest 199 * number of 'points'. We expect the caller will lock the tasklist. 200 * 201 * (not docbooked, we don't want this one cluttering up the manual) 202 */ 203static struct task_struct *select_bad_process(unsigned long *ppoints) 204{ 205 struct task_struct *g, *p; 206 struct task_struct *chosen = NULL; 207 struct timespec uptime; 208 *ppoints = 0; 209 210 do_posix_clock_monotonic_gettime(&uptime); 211 do_each_thread(g, p) { 212 unsigned long points; 213 214 /* 215 * skip kernel threads and tasks which have already released 216 * their mm. 217 */ 218 if (!p->mm) 219 continue; 220 /* skip the init task */ 221 if (is_init(p)) 222 continue; 223 224 /* 225 * This task already has access to memory reserves and is 226 * being killed. Don't allow any other task access to the 227 * memory reserve. 228 * 229 * Note: this may have a chance of deadlock if it gets 230 * blocked waiting for another task which itself is waiting 231 * for memory. Is there a better alternative? 232 */ 233 if (test_tsk_thread_flag(p, TIF_MEMDIE)) 234 return ERR_PTR(-1UL); 235 236 /* 237 * This is in the process of releasing memory so wait for it 238 * to finish before killing some other task by mistake. 239 * 240 * However, if p is the current task, we allow the 'kill' to 241 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 242 * which will allow it to gain access to memory reserves in 243 * the process of exiting and releasing its resources. 244 * Otherwise we could get an easy OOM deadlock. 245 */ 246 if (p->flags & PF_EXITING) { 247 if (p != current) 248 return ERR_PTR(-1UL); 249 250 chosen = p; 251 *ppoints = ULONG_MAX; 252 } 253 254 if (p->oomkilladj == OOM_DISABLE) 255 continue; 256 257 points = badness(p, uptime.tv_sec); 258 if (points > *ppoints || !chosen) { 259 chosen = p; 260 *ppoints = points; 261 } 262 } while_each_thread(g, p); 263 264 return chosen; 265} 266 267/** 268 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 269 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 270 * set. 271 */ 272static void __oom_kill_task(struct task_struct *p, int verbose) 273{ 274 if (is_init(p)) { 275 WARN_ON(1); 276 printk(KERN_WARNING "tried to kill init!\n"); 277 return; 278 } 279 280 if (!p->mm) { 281 WARN_ON(1); 282 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 283 return; 284 } 285 286 if (verbose) 287 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm); 288 289 /* 290 * We give our sacrificial lamb high priority and access to 291 * all the memory it needs. That way it should be able to 292 * exit() and clear out its resources quickly... 293 */ 294 p->time_slice = HZ; 295 set_tsk_thread_flag(p, TIF_MEMDIE); 296 297 force_sig(SIGKILL, p); 298} 299 300static int oom_kill_task(struct task_struct *p) 301{ 302 struct mm_struct *mm; 303 struct task_struct *g, *q; 304 305 mm = p->mm; 306 307 /* WARNING: mm may not be dereferenced since we did not obtain its 308 * value from get_task_mm(p). This is OK since all we need to do is 309 * compare mm to q->mm below. 310 * 311 * Furthermore, even if mm contains a non-NULL value, p->mm may 312 * change to NULL at any time since we do not hold task_lock(p). 313 * However, this is of no concern to us. 314 */ 315 316 if (mm == NULL) 317 return 1; 318 319 /* 320 * Don't kill the process if any threads are set to OOM_DISABLE 321 */ 322 do_each_thread(g, q) { 323 if (q->mm == mm && q->oomkilladj == OOM_DISABLE) 324 return 1; 325 } while_each_thread(g, q); 326 327 __oom_kill_task(p, 1); 328 329 /* 330 * kill all processes that share the ->mm (i.e. all threads), 331 * but are in a different thread group. Don't let them have access 332 * to memory reserves though, otherwise we might deplete all memory. 333 */ 334 do_each_thread(g, q) { 335 if (q->mm == mm && q->tgid != p->tgid) 336 force_sig(SIGKILL, p); 337 } while_each_thread(g, q); 338 339 return 0; 340} 341 342static int oom_kill_process(struct task_struct *p, unsigned long points, 343 const char *message) 344{ 345 struct task_struct *c; 346 struct list_head *tsk; 347 348 /* 349 * If the task is already exiting, don't alarm the sysadmin or kill 350 * its children or threads, just set TIF_MEMDIE so it can die quickly 351 */ 352 if (p->flags & PF_EXITING) { 353 __oom_kill_task(p, 0); 354 return 0; 355 } 356 357 printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n", 358 message, p->pid, p->comm, points); 359 360 /* Try to kill a child first */ 361 list_for_each(tsk, &p->children) { 362 c = list_entry(tsk, struct task_struct, sibling); 363 if (c->mm == p->mm) 364 continue; 365 if (!oom_kill_task(c)) 366 return 0; 367 } 368 return oom_kill_task(p); 369} 370 371static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 372 373int register_oom_notifier(struct notifier_block *nb) 374{ 375 return blocking_notifier_chain_register(&oom_notify_list, nb); 376} 377EXPORT_SYMBOL_GPL(register_oom_notifier); 378 379int unregister_oom_notifier(struct notifier_block *nb) 380{ 381 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 382} 383EXPORT_SYMBOL_GPL(unregister_oom_notifier); 384 385/** 386 * out_of_memory - kill the "best" process when we run out of memory 387 * 388 * If we run out of memory, we have the choice between either 389 * killing a random task (bad), letting the system crash (worse) 390 * OR try to be smart about which process to kill. Note that we 391 * don't have to be perfect here, we just have to be good. 392 */ 393void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 394{ 395 struct task_struct *p; 396 unsigned long points = 0; 397 unsigned long freed = 0; 398 399 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 400 if (freed > 0) 401 /* Got some memory back in the last second. */ 402 return; 403 404 if (printk_ratelimit()) { 405 printk(KERN_WARNING "%s invoked oom-killer: " 406 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 407 current->comm, gfp_mask, order, current->oomkilladj); 408 dump_stack(); 409 show_mem(); 410 } 411 412 cpuset_lock(); 413 read_lock(&tasklist_lock); 414 415 /* 416 * Check if there were limitations on the allocation (only relevant for 417 * NUMA) that may require different handling. 418 */ 419 switch (constrained_alloc(zonelist, gfp_mask)) { 420 case CONSTRAINT_MEMORY_POLICY: 421 oom_kill_process(current, points, 422 "No available memory (MPOL_BIND)"); 423 break; 424 425 case CONSTRAINT_CPUSET: 426 oom_kill_process(current, points, 427 "No available memory in cpuset"); 428 break; 429 430 case CONSTRAINT_NONE: 431 if (sysctl_panic_on_oom) 432 panic("out of memory. panic_on_oom is selected\n"); 433retry: 434 /* 435 * Rambo mode: Shoot down a process and hope it solves whatever 436 * issues we may have. 437 */ 438 p = select_bad_process(&points); 439 440 if (PTR_ERR(p) == -1UL) 441 goto out; 442 443 /* Found nothing?!?! Either we hang forever, or we panic. */ 444 if (!p) { 445 read_unlock(&tasklist_lock); 446 cpuset_unlock(); 447 panic("Out of memory and no killable processes...\n"); 448 } 449 450 if (oom_kill_process(p, points, "Out of memory")) 451 goto retry; 452 453 break; 454 } 455 456out: 457 read_unlock(&tasklist_lock); 458 cpuset_unlock(); 459 460 /* 461 * Give "p" a good chance of killing itself before we 462 * retry to allocate memory unless "p" is current 463 */ 464 if (!test_thread_flag(TIF_MEMDIE)) 465 schedule_timeout_uninterruptible(1); 466} 467