oom_kill.c revision 36c8b586896f60cb91a4fd526233190b34316baf
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 25int sysctl_panic_on_oom; 26/* #define DEBUG */ 27 28/** 29 * badness - calculate a numeric value for how bad this task has been 30 * @p: task struct of which task we should calculate 31 * @uptime: current uptime in seconds 32 * 33 * The formula used is relatively simple and documented inline in the 34 * function. The main rationale is that we want to select a good task 35 * to kill when we run out of memory. 36 * 37 * Good in this context means that: 38 * 1) we lose the minimum amount of work done 39 * 2) we recover a large amount of memory 40 * 3) we don't kill anything innocent of eating tons of memory 41 * 4) we want to kill the minimum amount of processes (one) 42 * 5) we try to kill the process the user expects us to kill, this 43 * algorithm has been meticulously tuned to meet the principle 44 * of least surprise ... (be careful when you change it) 45 */ 46 47unsigned long badness(struct task_struct *p, unsigned long uptime) 48{ 49 unsigned long points, cpu_time, run_time, s; 50 struct mm_struct *mm; 51 struct task_struct *child; 52 53 task_lock(p); 54 mm = p->mm; 55 if (!mm) { 56 task_unlock(p); 57 return 0; 58 } 59 60 /* 61 * The memory size of the process is the basis for the badness. 62 */ 63 points = mm->total_vm; 64 65 /* 66 * After this unlock we can no longer dereference local variable `mm' 67 */ 68 task_unlock(p); 69 70 /* 71 * Processes which fork a lot of child processes are likely 72 * a good choice. We add half the vmsize of the children if they 73 * have an own mm. This prevents forking servers to flood the 74 * machine with an endless amount of children. In case a single 75 * child is eating the vast majority of memory, adding only half 76 * to the parents will make the child our kill candidate of choice. 77 */ 78 list_for_each_entry(child, &p->children, sibling) { 79 task_lock(child); 80 if (child->mm != mm && child->mm) 81 points += child->mm->total_vm/2 + 1; 82 task_unlock(child); 83 } 84 85 /* 86 * CPU time is in tens of seconds and run time is in thousands 87 * of seconds. There is no particular reason for this other than 88 * that it turned out to work very well in practice. 89 */ 90 cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) 91 >> (SHIFT_HZ + 3); 92 93 if (uptime >= p->start_time.tv_sec) 94 run_time = (uptime - p->start_time.tv_sec) >> 10; 95 else 96 run_time = 0; 97 98 s = int_sqrt(cpu_time); 99 if (s) 100 points /= s; 101 s = int_sqrt(int_sqrt(run_time)); 102 if (s) 103 points /= s; 104 105 /* 106 * Niced processes are most likely less important, so double 107 * their badness points. 108 */ 109 if (task_nice(p) > 0) 110 points *= 2; 111 112 /* 113 * Superuser processes are usually more important, so we make it 114 * less likely that we kill those. 115 */ 116 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || 117 p->uid == 0 || p->euid == 0) 118 points /= 4; 119 120 /* 121 * We don't want to kill a process with direct hardware access. 122 * Not only could that mess up the hardware, but usually users 123 * tend to only have this flag set on applications they think 124 * of as important. 125 */ 126 if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) 127 points /= 4; 128 129 /* 130 * Adjust the score by oomkilladj. 131 */ 132 if (p->oomkilladj) { 133 if (p->oomkilladj > 0) 134 points <<= p->oomkilladj; 135 else 136 points >>= -(p->oomkilladj); 137 } 138 139#ifdef DEBUG 140 printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", 141 p->pid, p->comm, points); 142#endif 143 return points; 144} 145 146/* 147 * Types of limitations to the nodes from which allocations may occur 148 */ 149#define CONSTRAINT_NONE 1 150#define CONSTRAINT_MEMORY_POLICY 2 151#define CONSTRAINT_CPUSET 3 152 153/* 154 * Determine the type of allocation constraint. 155 */ 156static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask) 157{ 158#ifdef CONFIG_NUMA 159 struct zone **z; 160 nodemask_t nodes = node_online_map; 161 162 for (z = zonelist->zones; *z; z++) 163 if (cpuset_zone_allowed(*z, gfp_mask)) 164 node_clear((*z)->zone_pgdat->node_id, 165 nodes); 166 else 167 return CONSTRAINT_CPUSET; 168 169 if (!nodes_empty(nodes)) 170 return CONSTRAINT_MEMORY_POLICY; 171#endif 172 173 return CONSTRAINT_NONE; 174} 175 176/* 177 * Simple selection loop. We chose the process with the highest 178 * number of 'points'. We expect the caller will lock the tasklist. 179 * 180 * (not docbooked, we don't want this one cluttering up the manual) 181 */ 182static struct task_struct *select_bad_process(unsigned long *ppoints) 183{ 184 struct task_struct *g, *p; 185 struct task_struct *chosen = NULL; 186 struct timespec uptime; 187 *ppoints = 0; 188 189 do_posix_clock_monotonic_gettime(&uptime); 190 do_each_thread(g, p) { 191 unsigned long points; 192 int releasing; 193 194 /* skip the init task with pid == 1 */ 195 if (p->pid == 1) 196 continue; 197 if (p->oomkilladj == OOM_DISABLE) 198 continue; 199 /* If p's nodes don't overlap ours, it won't help to kill p. */ 200 if (!cpuset_excl_nodes_overlap(p)) 201 continue; 202 203 /* 204 * This is in the process of releasing memory so wait for it 205 * to finish before killing some other task by mistake. 206 */ 207 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) || 208 p->flags & PF_EXITING; 209 if (releasing && !(p->flags & PF_DEAD)) 210 return ERR_PTR(-1UL); 211 if (p->flags & PF_SWAPOFF) 212 return p; 213 214 points = badness(p, uptime.tv_sec); 215 if (points > *ppoints || !chosen) { 216 chosen = p; 217 *ppoints = points; 218 } 219 } while_each_thread(g, p); 220 return chosen; 221} 222 223/** 224 * We must be careful though to never send SIGKILL a process with 225 * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that 226 * we select a process with CAP_SYS_RAW_IO set). 227 */ 228static void __oom_kill_task(struct task_struct *p, const char *message) 229{ 230 if (p->pid == 1) { 231 WARN_ON(1); 232 printk(KERN_WARNING "tried to kill init!\n"); 233 return; 234 } 235 236 task_lock(p); 237 if (!p->mm || p->mm == &init_mm) { 238 WARN_ON(1); 239 printk(KERN_WARNING "tried to kill an mm-less task!\n"); 240 task_unlock(p); 241 return; 242 } 243 task_unlock(p); 244 printk(KERN_ERR "%s: Killed process %d (%s).\n", 245 message, p->pid, p->comm); 246 247 /* 248 * We give our sacrificial lamb high priority and access to 249 * all the memory it needs. That way it should be able to 250 * exit() and clear out its resources quickly... 251 */ 252 p->time_slice = HZ; 253 set_tsk_thread_flag(p, TIF_MEMDIE); 254 255 force_sig(SIGKILL, p); 256} 257 258static int oom_kill_task(struct task_struct *p, const char *message) 259{ 260 struct mm_struct *mm; 261 struct task_struct *g, *q; 262 263 mm = p->mm; 264 265 /* WARNING: mm may not be dereferenced since we did not obtain its 266 * value from get_task_mm(p). This is OK since all we need to do is 267 * compare mm to q->mm below. 268 * 269 * Furthermore, even if mm contains a non-NULL value, p->mm may 270 * change to NULL at any time since we do not hold task_lock(p). 271 * However, this is of no concern to us. 272 */ 273 274 if (mm == NULL || mm == &init_mm) 275 return 1; 276 277 __oom_kill_task(p, message); 278 /* 279 * kill all processes that share the ->mm (i.e. all threads), 280 * but are in a different thread group 281 */ 282 do_each_thread(g, q) 283 if (q->mm == mm && q->tgid != p->tgid) 284 __oom_kill_task(q, message); 285 while_each_thread(g, q); 286 287 return 0; 288} 289 290static int oom_kill_process(struct task_struct *p, unsigned long points, 291 const char *message) 292{ 293 struct task_struct *c; 294 struct list_head *tsk; 295 296 printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li and " 297 "children.\n", p->pid, p->comm, points); 298 /* Try to kill a child first */ 299 list_for_each(tsk, &p->children) { 300 c = list_entry(tsk, struct task_struct, sibling); 301 if (c->mm == p->mm) 302 continue; 303 if (!oom_kill_task(c, message)) 304 return 0; 305 } 306 return oom_kill_task(p, message); 307} 308 309/** 310 * out_of_memory - kill the "best" process when we run out of memory 311 * 312 * If we run out of memory, we have the choice between either 313 * killing a random task (bad), letting the system crash (worse) 314 * OR try to be smart about which process to kill. Note that we 315 * don't have to be perfect here, we just have to be good. 316 */ 317void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order) 318{ 319 struct task_struct *p; 320 unsigned long points = 0; 321 322 if (printk_ratelimit()) { 323 printk("oom-killer: gfp_mask=0x%x, order=%d\n", 324 gfp_mask, order); 325 dump_stack(); 326 show_mem(); 327 } 328 329 cpuset_lock(); 330 read_lock(&tasklist_lock); 331 332 /* 333 * Check if there were limitations on the allocation (only relevant for 334 * NUMA) that may require different handling. 335 */ 336 switch (constrained_alloc(zonelist, gfp_mask)) { 337 case CONSTRAINT_MEMORY_POLICY: 338 oom_kill_process(current, points, 339 "No available memory (MPOL_BIND)"); 340 break; 341 342 case CONSTRAINT_CPUSET: 343 oom_kill_process(current, points, 344 "No available memory in cpuset"); 345 break; 346 347 case CONSTRAINT_NONE: 348 if (sysctl_panic_on_oom) 349 panic("out of memory. panic_on_oom is selected\n"); 350retry: 351 /* 352 * Rambo mode: Shoot down a process and hope it solves whatever 353 * issues we may have. 354 */ 355 p = select_bad_process(&points); 356 357 if (PTR_ERR(p) == -1UL) 358 goto out; 359 360 /* Found nothing?!?! Either we hang forever, or we panic. */ 361 if (!p) { 362 read_unlock(&tasklist_lock); 363 cpuset_unlock(); 364 panic("Out of memory and no killable processes...\n"); 365 } 366 367 if (oom_kill_process(p, points, "Out of memory")) 368 goto retry; 369 370 break; 371 } 372 373out: 374 read_unlock(&tasklist_lock); 375 cpuset_unlock(); 376 377 /* 378 * Give "p" a good chance of killing itself before we 379 * retry to allocate memory unless "p" is current 380 */ 381 if (!test_thread_flag(TIF_MEMDIE)) 382 schedule_timeout_uninterruptible(1); 383} 384