mm/oom_kill.c

   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
  28 int 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
  50 unsigned 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          * swapoff can easily use up all memory, so kill those first.
  65          */
  66         if (p->flags & PF_SWAPOFF)
  67                 return ULONG_MAX;
  68
  69         /*
  70          * The memory size of the process is the basis for the badness.
  71          */
  72         points = mm->total_vm;
  73
  74         /*
  75          * After this unlock we can no longer dereference local variable `mm'
  76          */
  77         task_unlock(p);
  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  */
 173 static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
 174 {
 175 #ifdef CONFIG_NUMA
 176         struct zone **z;
 177         nodemask_t nodes = node_online_map;
 178
 179         for (z = zonelist->zones; *z; z++)
 180                 if (cpuset_zone_allowed(*z, gfp_mask))
 181                         node_clear(zone_to_nid(*z), nodes);
 182                 else
 183                         return CONSTRAINT_CPUSET;
 184
 185         if (!nodes_empty(nodes))
 186                 return CONSTRAINT_MEMORY_POLICY;
 187 #endif
 188
 189         return CONSTRAINT_NONE;
 190 }
 191
 192 /*
 193  * Simple selection loop. We chose the process with the highest
 194  * number of 'points'. We expect the caller will lock the tasklist.
 195  *
 196  * (not docbooked, we don't want this one cluttering up the manual)
 197  */
 198 static struct task_struct *select_bad_process(unsigned long *ppoints)
 199 {
 200         struct task_struct *g, *p;
 201         struct task_struct *chosen = NULL;
 202         struct timespec uptime;
 203         *ppoints = 0;
 204
 205         do_posix_clock_monotonic_gettime(&uptime);
 206         do_each_thread(g, p) {
 207                 unsigned long points;
 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 task already has access to memory reserves and is
 221                  * being killed. Don't allow any other task access to the
 222                  * memory reserve.
 223                  *
 224                  * Note: this may have a chance of deadlock if it gets
 225                  * blocked waiting for another task which itself is waiting
 226                  * for memory. Is there a better alternative?
 227                  */
 228                 if (test_tsk_thread_flag(p, TIF_MEMDIE))
 229                         return ERR_PTR(-1UL);
 230
 231                 /*
 232                  * This is in the process of releasing memory so wait for it
 233                  * to finish before killing some other task by mistake.
 234                  *
 235                  * However, if p is the current task, we allow the 'kill' to
 236                  * go ahead if it is exiting: this will simply set TIF_MEMDIE,
 237                  * which will allow it to gain access to memory reserves in
 238                  * the process of exiting and releasing its resources.
 239                  * Otherwise we could get an easy OOM deadlock.
 240                  */
 241                 if (p->flags & PF_EXITING) {
 242                         if (p != current)
 243                                 return ERR_PTR(-1UL);
 244
 245                         chosen = p;
 246                         *ppoints = ULONG_MAX;
 247                 }
 248
 249                 if (p->oomkilladj == OOM_DISABLE)
 250                         continue;
 251
 252                 points = badness(p, uptime.tv_sec);
 253                 if (points > *ppoints || !chosen) {
 254                         chosen = p;
 255                         *ppoints = points;
 256                 }
 257         } while_each_thread(g, p);
 258
 259         return chosen;
 260 }
 261
 262 /**
 263  * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
 264  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
 265  * set.
 266  */
 267 static void __oom_kill_task(struct task_struct *p, int verbose)
 268 {
 269         if (is_init(p)) {
 270                 WARN_ON(1);
 271                 printk(KERN_WARNING "tried to kill init!\n");
 272                 return;
 273         }
 274
 275         if (!p->mm) {
 276                 WARN_ON(1);
 277                 printk(KERN_WARNING "tried to kill an mm-less task!\n");
 278                 return;
 279         }
 280
 281         if (verbose)
 282                 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm);
 283
 284         /*
 285          * We give our sacrificial lamb high priority and access to
 286          * all the memory it needs. That way it should be able to
 287          * exit() and clear out its resources quickly...
 288          */
 289         p->time_slice = HZ;
 290         set_tsk_thread_flag(p, TIF_MEMDIE);
 291
 292         force_sig(SIGKILL, p);
 293 }
 294
 295 static int oom_kill_task(struct task_struct *p)
 296 {
 297         struct mm_struct *mm;
 298         struct task_struct *g, *q;
 299
 300         mm = p->mm;
 301
 302         /* WARNING: mm may not be dereferenced since we did not obtain its
 303          * value from get_task_mm(p).  This is OK since all we need to do is
 304          * compare mm to q->mm below.
 305          *
 306          * Furthermore, even if mm contains a non-NULL value, p->mm may
 307          * change to NULL at any time since we do not hold task_lock(p).
 308          * However, this is of no concern to us.
 309          */
 310
 311         if (mm == NULL)
 312                 return 1;
 313
 314         /*
 315          * Don't kill the process if any threads are set to OOM_DISABLE
 316          */
 317         do_each_thread(g, q) {
 318                 if (q->mm == mm && p->oomkilladj == OOM_DISABLE)
 319                         return 1;
 320         } while_each_thread(g, q);
 321
 322         __oom_kill_task(p, 1);
 323
 324         /*
 325          * kill all processes that share the ->mm (i.e. all threads),
 326          * but are in a different thread group. Don't let them have access
 327          * to memory reserves though, otherwise we might deplete all memory.
 328          */
 329         do_each_thread(g, q) {
 330                 if (q->mm == mm && q->tgid != p->tgid)
 331                         force_sig(SIGKILL, p);
 332         } while_each_thread(g, q);
 333
 334         return 0;
 335 }
 336
 337 static int oom_kill_process(struct task_struct *p, unsigned long points,
 338                 const char *message)
 339 {
 340         struct task_struct *c;
 341         struct list_head *tsk;
 342
 343         /*
 344          * If the task is already exiting, don't alarm the sysadmin or kill
 345          * its children or threads, just set TIF_MEMDIE so it can die quickly
 346          */
 347         if (p->flags & PF_EXITING) {
 348                 __oom_kill_task(p, 0);
 349                 return 0;
 350         }
 351
 352         printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
 353                                         message, p->pid, p->comm, points);
 354
 355         /* Try to kill a child first */
 356         list_for_each(tsk, &p->children) {
 357                 c = list_entry(tsk, struct task_struct, sibling);
 358                 if (c->mm == p->mm)
 359                         continue;
 360                 if (!oom_kill_task(c))
 361                         return 0;
 362         }
 363         return oom_kill_task(p);
 364 }
 365
 366 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
 367
 368 int register_oom_notifier(struct notifier_block *nb)
 369 {
 370         return blocking_notifier_chain_register(&oom_notify_list, nb);
 371 }
 372 EXPORT_SYMBOL_GPL(register_oom_notifier);
 373
 374 int unregister_oom_notifier(struct notifier_block *nb)
 375 {
 376         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
 377 }
 378 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
 379
 380 /**
 381  * out_of_memory - kill the "best" process when we run out of memory
 382  *
 383  * If we run out of memory, we have the choice between either
 384  * killing a random task (bad), letting the system crash (worse)
 385  * OR try to be smart about which process to kill. Note that we
 386  * don't have to be perfect here, we just have to be good.
 387  */
 388 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
 389 {
 390         struct task_struct *p;
 391         unsigned long points = 0;
 392         unsigned long freed = 0;
 393
 394         blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 395         if (freed > 0)
 396                 /* Got some memory back in the last second. */
 397                 return;
 398
 399         if (printk_ratelimit()) {
 400                 printk(KERN_WARNING "%s invoked oom-killer: "
 401                         "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
 402                         current->comm, gfp_mask, order, current->oomkilladj);
 403                 dump_stack();
 404                 show_mem();
 405         }
 406
 407         cpuset_lock();
 408         read_lock(&tasklist_lock);
 409
 410         /*
 411          * Check if there were limitations on the allocation (only relevant for
 412          * NUMA) that may require different handling.
 413          */
 414         switch (constrained_alloc(zonelist, gfp_mask)) {
 415         case CONSTRAINT_MEMORY_POLICY:
 416                 oom_kill_process(current, points,
 417                                 "No available memory (MPOL_BIND)");
 418                 break;
 419
 420         case CONSTRAINT_CPUSET:
 421                 oom_kill_process(current, points,
 422                                 "No available memory in cpuset");
 423                 break;
 424
 425         case CONSTRAINT_NONE:
 426                 if (sysctl_panic_on_oom)
 427                         panic("out of memory. panic_on_oom is selected\n");
 428 retry:
 429                 /*
 430                  * Rambo mode: Shoot down a process and hope it solves whatever
 431                  * issues we may have.
 432                  */
 433                 p = select_bad_process(&points);
 434
 435                 if (PTR_ERR(p) == -1UL)
 436                         goto out;
 437
 438                 /* Found nothing?!?! Either we hang forever, or we panic. */
 439                 if (!p) {
 440                         read_unlock(&tasklist_lock);
 441                         cpuset_unlock();
 442                         panic("Out of memory and no killable processes...\n");
 443                 }
 444
 445                 if (oom_kill_process(p, points, "Out of memory"))
 446                         goto retry;
 447
 448                 break;
 449         }
 450
 451 out:
 452         read_unlock(&tasklist_lock);
 453         cpuset_unlock();
 454
 455         /*
 456          * Give "p" a good chance of killing itself before we
 457          * retry to allocate memory unless "p" is current
 458          */
 459         if (!test_thread_flag(TIF_MEMDIE))
 460                 schedule_timeout_uninterruptible(1);
 461 }