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/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
  25 /* #define DEBUG */
  26
  27 /**
  28  * oom_badness - calculate a numeric value for how bad this task has been
  29  * @p: task struct of which task we should calculate
  30  * @uptime: current uptime in seconds
  31  *
  32  * The formula used is relatively simple and documented inline in the
  33  * function. The main rationale is that we want to select a good task
  34  * to kill when we run out of memory.
  35  *
  36  * Good in this context means that:
  37  * 1) we lose the minimum amount of work done
  38  * 2) we recover a large amount of memory
  39  * 3) we don't kill anything innocent of eating tons of memory
  40  * 4) we want to kill the minimum amount of processes (one)
  41  * 5) we try to kill the process the user expects us to kill, this
  42  *    algorithm has been meticulously tuned to meet the principle
  43  *    of least surprise ... (be careful when you change it)
  44  */
  45
  46 unsigned long badness(struct task_struct *p, unsigned long uptime)
  47 {
  48         unsigned long points, cpu_time, run_time, s;
  49         struct list_head *tsk;
  50
  51         if (!p->mm)
  52                 return 0;
  53
  54         /*
  55          * The memory size of the process is the basis for the badness.
  56          */
  57         points = p->mm->total_vm;
  58
  59         /*
  60          * Processes which fork a lot of child processes are likely
  61          * a good choice. We add the vmsize of the children if they
  62          * have an own mm. This prevents forking servers to flood the
  63          * machine with an endless amount of children
  64          */
  65         list_for_each(tsk, &p->children) {
  66                 struct task_struct *chld;
  67                 chld = list_entry(tsk, struct task_struct, sibling);
  68                 if (chld->mm != p->mm && chld->mm)
  69                         points += chld->mm->total_vm;
  70         }
  71
  72         /*
  73          * CPU time is in tens of seconds and run time is in thousands
  74          * of seconds. There is no particular reason for this other than
  75          * that it turned out to work very well in practice.
  76          */
  77         cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime))
  78                 >> (SHIFT_HZ + 3);
  79
  80         if (uptime >= p->start_time.tv_sec)
  81                 run_time = (uptime - p->start_time.tv_sec) >> 10;
  82         else
  83                 run_time = 0;
  84
  85         s = int_sqrt(cpu_time);
  86         if (s)
  87                 points /= s;
  88         s = int_sqrt(int_sqrt(run_time));
  89         if (s)
  90                 points /= s;
  91
  92         /*
  93          * Niced processes are most likely less important, so double
  94          * their badness points.
  95          */
  96         if (task_nice(p) > 0)
  97                 points *= 2;
  98
  99         /*
 100          * Superuser processes are usually more important, so we make it
 101          * less likely that we kill those.
 102          */
 103         if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) ||
 104                                 p->uid == 0 || p->euid == 0)
 105                 points /= 4;
 106
 107         /*
 108          * We don't want to kill a process with direct hardware access.
 109          * Not only could that mess up the hardware, but usually users
 110          * tend to only have this flag set on applications they think
 111          * of as important.
 112          */
 113         if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO))
 114                 points /= 4;
 115
 116         /*
 117          * Adjust the score by oomkilladj.
 118          */
 119         if (p->oomkilladj) {
 120                 if (p->oomkilladj > 0)
 121                         points <<= p->oomkilladj;
 122                 else
 123                         points >>= -(p->oomkilladj);
 124         }
 125
 126 #ifdef DEBUG
 127         printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
 128         p->pid, p->comm, points);
 129 #endif
 130         return points;
 131 }
 132
 133 /*
 134  * Simple selection loop. We chose the process with the highest
 135  * number of 'points'. We expect the caller will lock the tasklist.
 136  *
 137  * (not docbooked, we don't want this one cluttering up the manual)
 138  */
 139 static struct task_struct * select_bad_process(void)
 140 {
 141         unsigned long maxpoints = 0;
 142         struct task_struct *g, *p;
 143         struct task_struct *chosen = NULL;
 144         struct timespec uptime;
 145
 146         do_posix_clock_monotonic_gettime(&uptime);
 147         do_each_thread(g, p) {
 148                 unsigned long points;
 149                 int releasing;
 150
 151                 /* skip the init task with pid == 1 */
 152                 if (p->pid == 1)
 153                         continue;
 154                 if (p->oomkilladj == OOM_DISABLE)
 155                         continue;
 156                 /* If p's nodes don't overlap ours, it won't help to kill p. */
 157                 if (!cpuset_excl_nodes_overlap(p))
 158                         continue;
 159
 160                 /*
 161                  * This is in the process of releasing memory so for wait it
 162                  * to finish before killing some other task by mistake.
 163                  */
 164                 releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
 165                                                 p->flags & PF_EXITING;
 166                 if (releasing && !(p->flags & PF_DEAD))
 167                         return ERR_PTR(-1UL);
 168                 if (p->flags & PF_SWAPOFF)
 169                         return p;
 170
 171                 points = badness(p, uptime.tv_sec);
 172                 if (points > maxpoints || !chosen) {
 173                         chosen = p;
 174                         maxpoints = points;
 175                 }
 176         } while_each_thread(g, p);
 177         return chosen;
 178 }
 179
 180 /**
 181  * We must be careful though to never send SIGKILL a process with
 182  * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that
 183  * we select a process with CAP_SYS_RAW_IO set).
 184  */
 185 static void __oom_kill_task(task_t *p)
 186 {
 187         if (p->pid == 1) {
 188                 WARN_ON(1);
 189                 printk(KERN_WARNING "tried to kill init!\n");
 190                 return;
 191         }
 192
 193         task_lock(p);
 194         if (!p->mm || p->mm == &init_mm) {
 195                 WARN_ON(1);
 196                 printk(KERN_WARNING "tried to kill an mm-less task!\n");
 197                 task_unlock(p);
 198                 return;
 199         }
 200         task_unlock(p);
 201         printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n",
 202                                                         p->pid, p->comm);
 203
 204         /*
 205          * We give our sacrificial lamb high priority and access to
 206          * all the memory it needs. That way it should be able to
 207          * exit() and clear out its resources quickly...
 208          */
 209         p->time_slice = HZ;
 210         set_tsk_thread_flag(p, TIF_MEMDIE);
 211
 212         force_sig(SIGKILL, p);
 213 }
 214
 215 static struct mm_struct *oom_kill_task(task_t *p)
 216 {
 217         struct mm_struct *mm = get_task_mm(p);
 218         task_t * g, * q;
 219
 220         if (!mm)
 221                 return NULL;
 222         if (mm == &init_mm) {
 223                 mmput(mm);
 224                 return NULL;
 225         }
 226
 227         __oom_kill_task(p);
 228         /*
 229          * kill all processes that share the ->mm (i.e. all threads),
 230          * but are in a different thread group
 231          */
 232         do_each_thread(g, q)
 233                 if (q->mm == mm && q->tgid != p->tgid)
 234                         __oom_kill_task(q);
 235         while_each_thread(g, q);
 236
 237         return mm;
 238 }
 239
 240 static struct mm_struct *oom_kill_process(struct task_struct *p)
 241 {
 242         struct mm_struct *mm;
 243         struct task_struct *c;
 244         struct list_head *tsk;
 245
 246         /* Try to kill a child first */
 247         list_for_each(tsk, &p->children) {
 248                 c = list_entry(tsk, struct task_struct, sibling);
 249                 if (c->mm == p->mm)
 250                         continue;
 251                 mm = oom_kill_task(c);
 252                 if (mm)
 253                         return mm;
 254         }
 255         return oom_kill_task(p);
 256 }
 257
 258 /**
 259  * oom_kill - kill the "best" process when we run out of memory
 260  *
 261  * If we run out of memory, we have the choice between either
 262  * killing a random task (bad), letting the system crash (worse)
 263  * OR try to be smart about which process to kill. Note that we
 264  * don't have to be perfect here, we just have to be good.
 265  */
 266 void out_of_memory(gfp_t gfp_mask, int order)
 267 {
 268         struct mm_struct *mm = NULL;
 269         task_t * p;
 270
 271         if (printk_ratelimit()) {
 272                 printk("oom-killer: gfp_mask=0x%x, order=%d\n",
 273                         gfp_mask, order);
 274                 show_mem();
 275         }
 276
 277         cpuset_lock();
 278         read_lock(&tasklist_lock);
 279 retry:
 280         p = select_bad_process();
 281
 282         if (PTR_ERR(p) == -1UL)
 283                 goto out;
 284
 285         /* Found nothing?!?! Either we hang forever, or we panic. */
 286         if (!p) {
 287                 read_unlock(&tasklist_lock);
 288                 cpuset_unlock();
 289                 panic("Out of memory and no killable processes...\n");
 290         }
 291
 292         mm = oom_kill_process(p);
 293         if (!mm)
 294                 goto retry;
 295
 296  out:
 297         read_unlock(&tasklist_lock);
 298         cpuset_unlock();
 299         if (mm)
 300                 mmput(mm);
 301
 302         /*
 303          * Give "p" a good chance of killing itself before we
 304          * retry to allocate memory unless "p" is current
 305          */
 306         if (!test_thread_flag(TIF_MEMDIE))
 307                 schedule_timeout_interruptible(1);
 308 }