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          * 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  */
 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;
 178         int node;
 179
 180         nodes_clear(nodes);
 181         /* node has memory ? */
 182         for_each_online_node(node)
 183                 if (NODE_DATA(node)->node_present_pages)
 184                         node_set(node, nodes);
 185
 186         for (z = zonelist->zones; *z; z++)
 187                 if (cpuset_zone_allowed_softwall(*z, gfp_mask))
 188                         node_clear(zone_to_nid(*z), nodes);
 189                 else
 190                         return CONSTRAINT_CPUSET;
 191
 192         if (!nodes_empty(nodes))
 193                 return CONSTRAINT_MEMORY_POLICY;
 194 #endif
 195
 196         return CONSTRAINT_NONE;
 197 }
 198
 199 /*
 200  * Simple selection loop. We chose the process with the highest
 201  * number of 'points'. We expect the caller will lock the tasklist.
 202  *
 203  * (not docbooked, we don't want this one cluttering up the manual)
 204  */
 205 static struct task_struct *select_bad_process(unsigned long *ppoints)
 206 {
 207         struct task_struct *g, *p;
 208         struct task_struct *chosen = NULL;
 209         struct timespec uptime;
 210         *ppoints = 0;
 211
 212         do_posix_clock_monotonic_gettime(&uptime);
 213         do_each_thread(g, p) {
 214                 unsigned long points;
 215
 216                 /*
 217                  * skip kernel threads and tasks which have already released
 218                  * their mm.
 219                  */
 220                 if (!p->mm)
 221                         continue;
 222                 /* skip the init task */
 223                 if (is_init(p))
 224                         continue;
 225
 226                 /*
 227                  * This task already has access to memory reserves and is
 228                  * being killed. Don't allow any other task access to the
 229                  * memory reserve.
 230                  *
 231                  * Note: this may have a chance of deadlock if it gets
 232                  * blocked waiting for another task which itself is waiting
 233                  * for memory. Is there a better alternative?
 234                  */
 235                 if (test_tsk_thread_flag(p, TIF_MEMDIE))
 236                         return ERR_PTR(-1UL);
 237
 238                 /*
 239                  * This is in the process of releasing memory so wait for it
 240                  * to finish before killing some other task by mistake.
 241                  *
 242                  * However, if p is the current task, we allow the 'kill' to
 243                  * go ahead if it is exiting: this will simply set TIF_MEMDIE,
 244                  * which will allow it to gain access to memory reserves in
 245                  * the process of exiting and releasing its resources.
 246                  * Otherwise we could get an easy OOM deadlock.
 247                  */
 248                 if (p->flags & PF_EXITING) {
 249                         if (p != current)
 250                                 return ERR_PTR(-1UL);
 251
 252                         chosen = p;
 253                         *ppoints = ULONG_MAX;
 254                 }
 255
 256                 if (p->oomkilladj == OOM_DISABLE)
 257                         continue;
 258
 259                 points = badness(p, uptime.tv_sec);
 260                 if (points > *ppoints || !chosen) {
 261                         chosen = p;
 262                         *ppoints = points;
 263                 }
 264         } while_each_thread(g, p);
 265
 266         return chosen;
 267 }
 268
 269 /**
 270  * Send SIGKILL to the selected  process irrespective of  CAP_SYS_RAW_IO
 271  * flag though it's unlikely that  we select a process with CAP_SYS_RAW_IO
 272  * set.
 273  */
 274 static void __oom_kill_task(struct task_struct *p, int verbose)
 275 {
 276         if (is_init(p)) {
 277                 WARN_ON(1);
 278                 printk(KERN_WARNING "tried to kill init!\n");
 279                 return;
 280         }
 281
 282         if (!p->mm) {
 283                 WARN_ON(1);
 284                 printk(KERN_WARNING "tried to kill an mm-less task!\n");
 285                 return;
 286         }
 287
 288         if (verbose)
 289                 printk(KERN_ERR "Killed process %d (%s)\n", p->pid, p->comm);
 290
 291         /*
 292          * We give our sacrificial lamb high priority and access to
 293          * all the memory it needs. That way it should be able to
 294          * exit() and clear out its resources quickly...
 295          */
 296         p->time_slice = HZ;
 297         set_tsk_thread_flag(p, TIF_MEMDIE);
 298
 299         force_sig(SIGKILL, p);
 300 }
 301
 302 static int oom_kill_task(struct task_struct *p)
 303 {
 304         struct mm_struct *mm;
 305         struct task_struct *g, *q;
 306
 307         mm = p->mm;
 308
 309         /* WARNING: mm may not be dereferenced since we did not obtain its
 310          * value from get_task_mm(p).  This is OK since all we need to do is
 311          * compare mm to q->mm below.
 312          *
 313          * Furthermore, even if mm contains a non-NULL value, p->mm may
 314          * change to NULL at any time since we do not hold task_lock(p).
 315          * However, this is of no concern to us.
 316          */
 317
 318         if (mm == NULL)
 319                 return 1;
 320
 321         /*
 322          * Don't kill the process if any threads are set to OOM_DISABLE
 323          */
 324         do_each_thread(g, q) {
 325                 if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
 326                         return 1;
 327         } while_each_thread(g, q);
 328
 329         __oom_kill_task(p, 1);
 330
 331         /*
 332          * kill all processes that share the ->mm (i.e. all threads),
 333          * but are in a different thread group. Don't let them have access
 334          * to memory reserves though, otherwise we might deplete all memory.
 335          */
 336         do_each_thread(g, q) {
 337                 if (q->mm == mm && q->tgid != p->tgid)
 338                         force_sig(SIGKILL, q);
 339         } while_each_thread(g, q);
 340
 341         return 0;
 342 }
 343
 344 static int oom_kill_process(struct task_struct *p, unsigned long points,
 345                 const char *message)
 346 {
 347         struct task_struct *c;
 348         struct list_head *tsk;
 349
 350         /*
 351          * If the task is already exiting, don't alarm the sysadmin or kill
 352          * its children or threads, just set TIF_MEMDIE so it can die quickly
 353          */
 354         if (p->flags & PF_EXITING) {
 355                 __oom_kill_task(p, 0);
 356                 return 0;
 357         }
 358
 359         printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
 360                                         message, p->pid, p->comm, points);
 361
 362         /* Try to kill a child first */
 363         list_for_each(tsk, &p->children) {
 364                 c = list_entry(tsk, struct task_struct, sibling);
 365                 if (c->mm == p->mm)
 366                         continue;
 367                 if (!oom_kill_task(c))
 368                         return 0;
 369         }
 370         return oom_kill_task(p);
 371 }
 372
 373 static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
 374
 375 int register_oom_notifier(struct notifier_block *nb)
 376 {
 377         return blocking_notifier_chain_register(&oom_notify_list, nb);
 378 }
 379 EXPORT_SYMBOL_GPL(register_oom_notifier);
 380
 381 int unregister_oom_notifier(struct notifier_block *nb)
 382 {
 383         return blocking_notifier_chain_unregister(&oom_notify_list, nb);
 384 }
 385 EXPORT_SYMBOL_GPL(unregister_oom_notifier);
 386
 387 /**
 388  * out_of_memory - kill the "best" process when we run out of memory
 389  *
 390  * If we run out of memory, we have the choice between either
 391  * killing a random task (bad), letting the system crash (worse)
 392  * OR try to be smart about which process to kill. Note that we
 393  * don't have to be perfect here, we just have to be good.
 394  */
 395 void out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, int order)
 396 {
 397         struct task_struct *p;
 398         unsigned long points = 0;
 399         unsigned long freed = 0;
 400
 401         blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
 402         if (freed > 0)
 403                 /* Got some memory back in the last second. */
 404                 return;
 405
 406         if (printk_ratelimit()) {
 407                 printk(KERN_WARNING "%s invoked oom-killer: "
 408                         "gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
 409                         current->comm, gfp_mask, order, current->oomkilladj);
 410                 dump_stack();
 411                 show_mem();
 412         }
 413
 414         cpuset_lock();
 415         read_lock(&tasklist_lock);
 416
 417         /*
 418          * Check if there were limitations on the allocation (only relevant for
 419          * NUMA) that may require different handling.
 420          */
 421         switch (constrained_alloc(zonelist, gfp_mask)) {
 422         case CONSTRAINT_MEMORY_POLICY:
 423                 oom_kill_process(current, points,
 424                                 "No available memory (MPOL_BIND)");
 425                 break;
 426
 427         case CONSTRAINT_CPUSET:
 428                 oom_kill_process(current, points,
 429                                 "No available memory in cpuset");
 430                 break;
 431
 432         case CONSTRAINT_NONE:
 433                 if (sysctl_panic_on_oom)
 434                         panic("out of memory. panic_on_oom is selected\n");
 435 retry:
 436                 /*
 437                  * Rambo mode: Shoot down a process and hope it solves whatever
 438                  * issues we may have.
 439                  */
 440                 p = select_bad_process(&points);
 441
 442                 if (PTR_ERR(p) == -1UL)
 443                         goto out;
 444
 445                 /* Found nothing?!?! Either we hang forever, or we panic. */
 446                 if (!p) {
 447                         read_unlock(&tasklist_lock);
 448                         cpuset_unlock();
 449                         panic("Out of memory and no killable processes...\n");
 450                 }
 451
 452                 if (oom_kill_process(p, points, "Out of memory"))
 453                         goto retry;
 454
 455                 break;
 456         }
 457
 458 out:
 459         read_unlock(&tasklist_lock);
 460         cpuset_unlock();
 461
 462         /*
 463          * Give "p" a good chance of killing itself before we
 464          * retry to allocate memory unless "p" is current
 465          */
 466         if (!test_thread_flag(TIF_MEMDIE))
 467                 schedule_timeout_uninterruptible(1);
 468 }