oom_kill.c revision 28324d1df646521256e83389244adcce98e89ff2
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/mm.h> 19#include <linux/sched.h> 20#include <linux/swap.h> 21#include <linux/timex.h> 22#include <linux/jiffies.h> 23#include <linux/cpuset.h> 24#include <linux/module.h> 25#include <linux/notifier.h> 26 27int sysctl_panic_on_oom; 28/* #define DEBUG */ 29 30/** 31 * badness - calculate a numeric value for how bad this task has been 32 * @p: task struct of which task we should calculate 33 * @uptime: current uptime in seconds 34 * 35 * The formula used is relatively simple and documented inline in the 36 * function. The main rationale is that we want to select a good task 37 * to kill when we run out of memory. 38 * 39 * Good in this context means that: 40 * 1) we lose the minimum amount of work done 41 * 2) we recover a large amount of memory 42 * 3) we don't kill anything innocent of eating tons of memory 43 * 4) we want to kill the minimum amount of processes (one) 44 * 5) we try to kill the process the user expects us to kill, this 45 * algorithm has been meticulously tuned to meet the principle 46 * of least surprise ... (be careful when you change it) 47 */ 48 49unsigned long badness(struct task_struct *p, unsigned long uptime) 50{ 51 unsigned long points, cpu_time, run_time, s; 52 struct mm_struct *mm; 53 struct task_struct *child; 54 55 task_lock(p); 56 mm = p->mm; 57 if (!mm) { 58 task_unlock(p); 59 return 0; 60 } 61 62 /* 63 * swapoff can easily use up all memory, so kill those first. 64 */ 65 if (p->flags & PF_SWAPOFF) 66 return ULONG_MAX; 67 68 /* 69 * The memory size of the process is the basis for the badness. 70 */ 71 points = mm->total_vm; 72 73 /* 74 * After this unlock we can no longer dereference local variable `mm' 75 */ 76 task_unlock(p); 77 78 /* 79 * Processes which fork a lot of child processes are likely 80 * a good choice. We add half the vmsize of the children if they 81 * have an own mm. This prevents forking servers to flood the 82 * machine with an endless amount of children. In case a single 83 * child is eating the vast majority of memory, adding only half 84 * to the parents will make the child our kill candidate of choice. 85 */ 86 list_for_each_entry(child, &p->children, sibling) { 87 task_lock(child); 88 if (child->mm != mm && child->mm) 89 points += child->mm->total_vm/2 + 1; 90 task_unlock(child); 91 } 92 93 /* 94 * CPU time is in tens of seconds and run time is in thousands 95 * of seconds. There is no particular reason for this other than 96 * that it turned out to work very well in practice. 97 */ 98 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 99 >> (SHIFT_HZ + 3); 100 101 if (uptime >= p->start_time.tv_sec) 102 run_time = (uptime - p->start_time.tv_sec) >> 10; 103 else 104 run_time = 0; 105 106 s = int_sqrt(cpu_time); 107 if (s) 108 points /= s; 109 s = int_sqrt(int_sqrt(run_time)); 110 if (s) 111 points /= s; 112 113 /* 114 * Niced processes are most likely less important, so double 115 * their badness points. 116 */ 117 if (task_nice(p) > 0) 118 points *= 2; 119 120 /* 121 * Superuser processes are usually more important, so we make it 122 * less likely that we kill those. 123 */ 124 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 125 p->uid == 0 || p->euid == 0) 126 points /= 4; 127 128 /* 129 * We don't want to kill a process with direct hardware access. 130 * Not only could that mess up the hardware, but usually users 131 * tend to only have this flag set on applications they think 132 * of as important. 133 */ 134 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 135 points /= 4; 136 137 /* 138 * If p's nodes don't overlap ours, it may still help to kill p 139 * because p may have allocated or otherwise mapped memory on 140 * this node before. However it will be less likely. 141 */ 142 if (!cpuset_excl_nodes_overlap(p)) 143 points /= 8; 144 145 /* 146 * Adjust the score by oomkilladj. 147 */ 148 if (p->oomkilladj) { 149 if (p->oomkilladj > 0) 150 points <<= p->oomkilladj; 151 else 152 points >>= -(p->oomkilladj); 153 } 154 155#ifdef DEBUG 156 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 157 p->pid, p->comm, points); 158#endif 159 return points; 160} 161 162/* 163 * Types of limitations to the nodes from which allocations may occur 164 */ 165#define CONSTRAINT_NONE 1 166#define CONSTRAINT_MEMORY_POLICY 2 167#define CONSTRAINT_CPUSET 3 168 169/* 170 * Determine the type of allocation constraint. 171 */ 172static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 173{ 174#ifdef CONFIG_NUMA 175 struct zone **z; 176 nodemask_t nodes = node_online_map; 177 178 for (z = zonelist->zones; *z; z++) 179 if (cpuset_zone_allowed(*z, gfp_mask)) 180 node_clear(zone_to_nid(*z), nodes); 181 else 182 return CONSTRAINT_CPUSET; 183 184 if (!nodes_empty(nodes)) 185 return CONSTRAINT_MEMORY_POLICY; 186#endif 187 188 return CONSTRAINT_NONE; 189} 190 191/* 192 * Simple selection loop. We chose the process with the highest 193 * number of 'points'. We expect the caller will lock the tasklist. 194 * 195 * (not docbooked, we don't want this one cluttering up the manual) 196 */ 197static struct task_struct *select_bad_process(unsigned long *ppoints) 198{ 199 struct task_struct *g, *p; 200 struct task_struct *chosen = NULL; 201 struct timespec uptime; 202 *ppoints = 0; 203 204 do_posix_clock_monotonic_gettime(&uptime); 205 do_each_thread(g, p) { 206 unsigned long points; 207 int releasing; 208 209 /* 210 * skip kernel threads and tasks which have already released 211 * their mm. 212 */ 213 if (!p->mm) 214 continue; 215 /* skip the init task */ 216 if (is_init(p)) 217 continue; 218 219 /* 220 * This is in the process of releasing memory so wait for it 221 * to finish before killing some other task by mistake. 222 * 223 * However, if p is the current task, we allow the 'kill' to 224 * go ahead if it is exiting: this will simply set TIF_MEMDIE, 225 * which will allow it to gain access to memory reserves in 226 * the process of exiting and releasing its resources. 227 * Otherwise we could get an OOM deadlock. 228 */ 229 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) || 230 p->flags & PF_EXITING; 231 if (releasing) { 232 if (p->flags & PF_EXITING && p == current) { 233 chosen = p; 234 *ppoints = ULONG_MAX; 235 break; 236 } 237 return ERR_PTR(-1UL); 238 } 239 if (p->oomkilladj == OOM_DISABLE) 240 continue; 241 242 points = badness(p, uptime.tv_sec); 243 if (points > *ppoints || !chosen) { 244 chosen = p; 245 *ppoints = points; 246 } 247 } while_each_thread(g, p); 248 return chosen; 249} 250 251/** 252 * Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO 253 * flag though it's unlikely that we select a process with CAP_SYS_RAW_IO 254 * set. 255 */ 256static void __oom_kill_task(struct task_struct *p, const char *message) 257{ 258 if (is_init(p)) { 259 WARN_ON(1); 260 printk(KERN_WARNING "tried to kill init!\n"); 261 return; 262 } 263 264 task_lock(p); 265 if (!p->mm || p->mm == &init_mm) { 266 WARN_ON(1); 267 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 268 task_unlock(p); 269 return; 270 } 271 task_unlock(p); 272 273 if (message) { 274 printk(KERN_ERR "%s: Killed process %d (%s).\n", 275 message, p->pid, p->comm); 276 } 277 278 /* 279 * We give our sacrificial lamb high priority and access to 280 * all the memory it needs. That way it should be able to 281 * exit() and clear out its resources quickly... 282 */ 283 p->time_slice = HZ; 284 set_tsk_thread_flag(p, TIF_MEMDIE); 285 286 force_sig(SIGKILL, p); 287} 288 289static int oom_kill_task(struct task_struct *p, const char *message) 290{ 291 struct mm_struct *mm; 292 struct task_struct *g, *q; 293 294 mm = p->mm; 295 296 /* WARNING: mm may not be dereferenced since we did not obtain its 297 * value from get_task_mm(p). This is OK since all we need to do is 298 * compare mm to q->mm below. 299 * 300 * Furthermore, even if mm contains a non-NULL value, p->mm may 301 * change to NULL at any time since we do not hold task_lock(p). 302 * However, this is of no concern to us. 303 */ 304 305 if (mm == NULL || mm == &init_mm) 306 return 1; 307 308 __oom_kill_task(p, message); 309 /* 310 * kill all processes that share the ->mm (i.e. all threads), 311 * but are in a different thread group 312 */ 313 do_each_thread(g, q) 314 if (q->mm == mm && q->tgid != p->tgid) 315 __oom_kill_task(q, message); 316 while_each_thread(g, q); 317 318 return 0; 319} 320 321static int oom_kill_process(struct task_struct *p, unsigned long points, 322 const char *message) 323{ 324 struct task_struct *c; 325 struct list_head *tsk; 326 327 /* 328 * If the task is already exiting, don't alarm the sysadmin or kill 329 * its children or threads, just set TIF_MEMDIE so it can die quickly 330 */ 331 if (p->flags & PF_EXITING) { 332 __oom_kill_task(p, NULL); 333 return 0; 334 } 335 336 printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li" 337 " and children.\n", p->pid, p->comm, points); 338 /* Try to kill a child first */ 339 list_for_each(tsk, &p->children) { 340 c = list_entry(tsk, struct task_struct, sibling); 341 if (c->mm == p->mm) 342 continue; 343 if (!oom_kill_task(c, message)) 344 return 0; 345 } 346 return oom_kill_task(p, message); 347} 348 349static BLOCKING_NOTIFIER_HEAD(oom_notify_list); 350 351int register_oom_notifier(struct notifier_block *nb) 352{ 353 return blocking_notifier_chain_register(&oom_notify_list, nb); 354} 355EXPORT_SYMBOL_GPL(register_oom_notifier); 356 357int unregister_oom_notifier(struct notifier_block *nb) 358{ 359 return blocking_notifier_chain_unregister(&oom_notify_list, nb); 360} 361EXPORT_SYMBOL_GPL(unregister_oom_notifier); 362 363/** 364 * out_of_memory - kill the "best" process when we run out of memory 365 * 366 * If we run out of memory, we have the choice between either 367 * killing a random task (bad), letting the system crash (worse) 368 * OR try to be smart about which process to kill. Note that we 369 * don't have to be perfect here, we just have to be good. 370 */ 371void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 372{ 373 struct task_struct *p; 374 unsigned long points = 0; 375 unsigned long freed = 0; 376 377 blocking_notifier_call_chain(&oom_notify_list, 0, &freed); 378 if (freed > 0) 379 /* Got some memory back in the last second. */ 380 return; 381 382 if (printk_ratelimit()) { 383 printk(KERN_WARNING "%s invoked oom-killer: " 384 "gfp_mask=0x%x, order=%d, oomkilladj=%d\n", 385 current->comm, gfp_mask, order, current->oomkilladj); 386 dump_stack(); 387 show_mem(); 388 } 389 390 cpuset_lock(); 391 read_lock(&tasklist_lock); 392 393 /* 394 * Check if there were limitations on the allocation (only relevant for 395 * NUMA) that may require different handling. 396 */ 397 switch (constrained_alloc(zonelist, gfp_mask)) { 398 case CONSTRAINT_MEMORY_POLICY: 399 oom_kill_process(current, points, 400 "No available memory (MPOL_BIND)"); 401 break; 402 403 case CONSTRAINT_CPUSET: 404 oom_kill_process(current, points, 405 "No available memory in cpuset"); 406 break; 407 408 case CONSTRAINT_NONE: 409 if (sysctl_panic_on_oom) 410 panic("out of memory. panic_on_oom is selected\n"); 411retry: 412 /* 413 * Rambo mode: Shoot down a process and hope it solves whatever 414 * issues we may have. 415 */ 416 p = select_bad_process(&points); 417 418 if (PTR_ERR(p) == -1UL) 419 goto out; 420 421 /* Found nothing?!?! Either we hang forever, or we panic. */ 422 if (!p) { 423 read_unlock(&tasklist_lock); 424 cpuset_unlock(); 425 panic("Out of memory and no killable processes...\n"); 426 } 427 428 if (oom_kill_process(p, points, "Out of memory")) 429 goto retry; 430 431 break; 432 } 433 434out: 435 read_unlock(&tasklist_lock); 436 cpuset_unlock(); 437 438 /* 439 * Give "p" a good chance of killing itself before we 440 * retry to allocate memory unless "p" is current 441 */ 442 if (!test_thread_flag(TIF_MEMDIE)) 443 schedule_timeout_uninterruptible(1); 444} 445