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 kswapd()
  10  *  in linux/mm/vmscan.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
  24 /* #define DEBUG */
  25
  26 /**
  27  * oom_badness - calculate a numeric value for how bad this task has been
  28  * @p: task struct of which task we should calculate
  29  * @p: current uptime in seconds
  30  *
  31  * The formula used is relatively simple and documented inline in the
  32  * function. The main rationale is that we want to select a good task
  33  * to kill when we run out of memory.
  34  *
  35  * Good in this context means that:
  36  * 1) we lose the minimum amount of work done
  37  * 2) we recover a large amount of memory
  38  * 3) we don't kill anything innocent of eating tons of memory
  39  * 4) we want to kill the minimum amount of processes (one)
  40  * 5) we try to kill the process the user expects us to kill, this
  41  *    algorithm has been meticulously tuned to meet the principle
  42  *    of least surprise ... (be careful when you change it)
  43  */
  44
  45 unsigned long badness(struct task_struct *p, unsigned long uptime)
  46 {
  47         unsigned long points, cpu_time, run_time, s;
  48         struct list_head *tsk;
  49
  50         if (!p->mm)
  51                 return 0;
  52
  53         /*
  54          * The memory size of the process is the basis for the badness.
  55          */
  56         points = p->mm->total_vm;
  57
  58         /*
  59          * Processes which fork a lot of child processes are likely
  60          * a good choice. We add the vmsize of the childs if they
  61          * have an own mm. This prevents forking servers to flood the
  62          * machine with an endless amount of childs
  63          */
  64         list_for_each(tsk, &p->children) {
  65                 struct task_struct *chld;
  66                 chld = list_entry(tsk, struct task_struct, sibling);
  67                 if (chld->mm != p->mm && chld->mm)
  68                         points += chld->mm->total_vm;
  69         }
  70
  71         /*
  72          * CPU time is in tens of seconds and run time is in thousands
  73          * of seconds. There is no particular reason for this other than
  74          * that it turned out to work very well in practice.
  75          */
  76         cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
  77                 >> (SHIFT_HZ + 3);
  78
  79         if (uptime >= p->start_time.tv_sec)
  80                 run_time = (uptime - p->start_time.tv_sec) >> 10;
  81         else
  82                 run_time = 0;
  83
  84         s = int_sqrt(cpu_time);
  85         if (s)
  86                 points /= s;
  87         s = int_sqrt(int_sqrt(run_time));
  88         if (s)
  89                 points /= s;
  90
  91         /*
  92          * Niced processes are most likely less important, so double
  93          * their badness points.
  94          */
  95         if (task_nice(p) > 0)
  96                 points *= 2;
  97
  98         /*
  99          * Superuser processes are usually more important, so we make it
 100          * less likely that we kill those.
 101          */
 102         if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
 103                                 p->uid == 0 || p->euid == 0)
 104                 points /= 4;
 105
 106         /*
 107          * We don't want to kill a process with direct hardware access.
 108          * Not only could that mess up the hardware, but usually users
 109          * tend to only have this flag set on applications they think
 110          * of as important.
 111          */
 112         if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
 113                 points /= 4;
 114
 115         /*
 116          * Adjust the score by oomkilladj.
 117          */
 118         if (p->oomkilladj) {
 119                 if (p->oomkilladj > 0)
 120                         points <<= p->oomkilladj;
 121                 else
 122                         points >>= -(p->oomkilladj);
 123         }
 124
 125 #ifdef DEBUG
 126         printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
 127         p->pid, p->comm, points);
 128 #endif
 129         return points;
 130 }
 131
 132 /*
 133  * Simple selection loop. We chose the process with the highest
 134  * number of 'points'. We expect the caller will lock the tasklist.
 135  *
 136  * (not docbooked, we don't want this one cluttering up the manual)
 137  */
 138 static struct task_struct * select_bad_process(void)
 139 {
 140         unsigned long maxpoints = 0;
 141         struct task_struct *g, *p;
 142         struct task_struct *chosen = NULL;
 143         struct timespec uptime;
 144
 145         do_posix_clock_monotonic_gettime(&uptime);
 146         do_each_thread(g, p)
 147                 /* skip the init task with pid == 1 */
 148                 if (p->pid > 1 && p->oomkilladj != OOM_DISABLE) {
 149                         unsigned long points;
 150
 151                         /*
 152                          * This is in the process of releasing memory so wait it
 153                          * to finish before killing some other task by mistake.
 154                          */
 155                         if ((unlikely(test_tsk_thread_flag(p, TIF_MEMDIE)) || (p->flags & PF_EXITING)) &&
 156                             !(p->flags & PF_DEAD))
 157                                 return ERR_PTR(-1UL);
 158                         if (p->flags & PF_SWAPOFF)
 159                                 return p;
 160
 161                         points = badness(p, uptime.tv_sec);
 162                         if (points > maxpoints || !chosen) {
 163                                 chosen = p;
 164                                 maxpoints = points;
 165                         }
 166                 }
 167         while_each_thread(g, p);
 168         return chosen;
 169 }
 170
 171 /**
 172  * We must be careful though to never send SIGKILL a process with
 173  * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
 174  * we select a process with CAP_SYS_RAW_IO set).
 175  */
 176 static void __oom_kill_task(task_t *p)
 177 {
 178         if (p->pid == 1) {
 179                 WARN_ON(1);
 180                 printk(KERN_WARNING "tried to kill init!\n");
 181                 return;
 182         }
 183
 184         task_lock(p);
 185         if (!p->mm || p->mm == &init_mm) {
 186                 WARN_ON(1);
 187                 printk(KERN_WARNING "tried to kill an mm-less task!\n");
 188                 task_unlock(p);
 189                 return;
 190         }
 191         task_unlock(p);
 192         printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", p->pid, p->comm);
 193
 194         /*
 195          * We give our sacrificial lamb high priority and access to
 196          * all the memory it needs. That way it should be able to
 197          * exit() and clear out its resources quickly...
 198          */
 199         p->time_slice = HZ;
 200         set_tsk_thread_flag(p, TIF_MEMDIE);
 201
 202         force_sig(SIGKILL, p);
 203 }
 204
 205 static struct mm_struct *oom_kill_task(task_t *p)
 206 {
 207         struct mm_struct *mm = get_task_mm(p);
 208         task_t * g, * q;
 209
 210         if (!mm)
 211                 return NULL;
 212         if (mm == &init_mm) {
 213                 mmput(mm);
 214                 return NULL;
 215         }
 216
 217         __oom_kill_task(p);
 218         /*
 219          * kill all processes that share the ->mm (i.e. all threads),
 220          * but are in a different thread group
 221          */
 222         do_each_thread(g, q)
 223                 if (q->mm == mm && q->tgid != p->tgid)
 224                         __oom_kill_task(q);
 225         while_each_thread(g, q);
 226
 227         return mm;
 228 }
 229
 230 static struct mm_struct *oom_kill_process(struct task_struct *p)
 231 {
 232         struct mm_struct *mm;
 233         struct task_struct *c;
 234         struct list_head *tsk;
 235
 236         /* Try to kill a child first */
 237         list_for_each(tsk, &p->children) {
 238                 c = list_entry(tsk, struct task_struct, sibling);
 239                 if (c->mm == p->mm)
 240                         continue;
 241                 mm = oom_kill_task(c);
 242                 if (mm)
 243                         return mm;
 244         }
 245         return oom_kill_task(p);
 246 }
 247
 248 /**
 249  * oom_kill - kill the "best" process when we run out of memory
 250  *
 251  * If we run out of memory, we have the choice between either
 252  * killing a random task (bad), letting the system crash (worse)
 253  * OR try to be smart about which process to kill. Note that we
 254  * don't have to be perfect here, we just have to be good.
 255  */
 256 void out_of_memory(unsigned int __nocast gfp_mask)
 257 {
 258         struct mm_struct *mm = NULL;
 259         task_t * p;
 260
 261         printk("oom-killer: gfp_mask=0x%x\n", gfp_mask);
 262         /* print memory stats */
 263         show_mem();
 264
 265         read_lock(&tasklist_lock);
 266 retry:
 267         p = select_bad_process();
 268
 269         if (PTR_ERR(p) == -1UL)
 270                 goto out;
 271
 272         /* Found nothing?!?! Either we hang forever, or we panic. */
 273         if (!p) {
 274                 read_unlock(&tasklist_lock);
 275                 panic("Out of memory and no killable processes...\n");
 276         }
 277
 278         mm = oom_kill_process(p);
 279         if (!mm)
 280                 goto retry;
 281
 282  out:
 283         read_unlock(&tasklist_lock);
 284         if (mm)
 285                 mmput(mm);
 286
 287         /*
 288          * Give "p" a good chance of killing itself before we
 289          * retry to allocate memory.
 290          */
 291         __set_current_state(TASK_INTERRUPTIBLE);
 292         schedule_timeout(1);
 293 }