/* * linux/mm/oom_kill.c * * Copyright (C) 1998,2000 Rik van Riel * Thanks go out to Claus Fischer for some serious inspiration and * for goading me into coding this file... * * The routines in this file are used to kill a process when * we're seriously out of memory. This gets called from kswapd() * in linux/mm/vmscan.c when we really run out of memory. * * Since we won't call these routines often (on a well-configured * machine) this file will double as a 'coding guide' and a signpost * for newbie kernel hackers. It features several pointers to major * kernel subsystems and hints as to where to find out what things do. */ #include <linux/mm.h> #include <linux/sched.h> #include <linux/swap.h> #include <linux/timex.h> #include <linux/jiffies.h> /* #define DEBUG */ /** * oom_badness - calculate a numeric value for how bad this task has been * @p: task struct of which task we should calculate * @p: current uptime in seconds * * The formula used is relatively simple and documented inline in the * function. The main rationale is that we want to select a good task * to kill when we run out of memory. * * Good in this context means that: * 1) we lose the minimum amount of work done * 2) we recover a large amount of memory * 3) we don't kill anything innocent of eating tons of memory * 4) we want to kill the minimum amount of processes (one) * 5) we try to kill the process the user expects us to kill, this * algorithm has been meticulously tuned to meet the principle * of least surprise ... (be careful when you change it) */ unsigned long badness(struct task_struct *p, unsigned long uptime) { unsigned long points, cpu_time, run_time, s; struct list_head *tsk; if (!p->mm) return 0; /* * The memory size of the process is the basis for the badness. */ points = p->mm->total_vm; /* * Processes which fork a lot of child processes are likely * a good choice. We add the vmsize of the childs if they * have an own mm. This prevents forking servers to flood the * machine with an endless amount of childs */ list_for_each(tsk, &p->children) { struct task_struct *chld; chld = list_entry(tsk, struct task_struct, sibling); if (chld->mm != p->mm && chld->mm) points += chld->mm->total_vm; } /* * CPU time is in tens of seconds and run time is in thousands * of seconds. There is no particular reason for this other than * that it turned out to work very well in practice. */ cpu_time = (cputime_to_jiffies(p->utime) + cputime_to_jiffies(p->stime)) >> (SHIFT_HZ + 3); if (uptime >= p->start_time.tv_sec) run_time = (uptime - p->start_time.tv_sec) >> 10; else run_time = 0; s = int_sqrt(cpu_time); if (s) points /= s; s = int_sqrt(int_sqrt(run_time)); if (s) points /= s; /* * Niced processes are most likely less important, so double * their badness points. */ if (task_nice(p) > 0) points *= 2; /* * Superuser processes are usually more important, so we make it * less likely that we kill those. */ if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_ADMIN) || p->uid == 0 || p->euid == 0) points /= 4; /* * We don't want to kill a process with direct hardware access. * Not only could that mess up the hardware, but usually users * tend to only have this flag set on applications they think * of as important. */ if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) points /= 4; /* * Adjust the score by oomkilladj. */ if (p->oomkilladj) { if (p->oomkilladj > 0) points <<= p->oomkilladj; else points >>= -(p->oomkilladj); } #ifdef DEBUG printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n", p->pid, p->comm, points); #endif return points; } /* * Simple selection loop. We chose the process with the highest * number of 'points'. We expect the caller will lock the tasklist. * * (not docbooked, we don't want this one cluttering up the manual) */ static struct task_struct * select_bad_process(void) { unsigned long maxpoints = 0; struct task_struct *g, *p; struct task_struct *chosen = NULL; struct timespec uptime; do_posix_clock_monotonic_gettime(&uptime); do_each_thread(g, p) /* skip the init task with pid == 1 */ if (p->pid > 1 && p->oomkilladj != OOM_DISABLE) { unsigned long points; /* * This is in the process of releasing memory so wait it * to finish before killing some other task by mistake. */ if ((unlikely(test_tsk_thread_flag(p, TIF_MEMDIE)) || (p->flags & PF_EXITING)) && !(p->flags & PF_DEAD)) return ERR_PTR(-1UL); if (p->flags & PF_SWAPOFF) return p; points = badness(p, uptime.tv_sec); if (points > maxpoints || !chosen) { chosen = p; maxpoints = points; } } while_each_thread(g, p); return chosen; } /** * We must be careful though to never send SIGKILL a process with * CAP_SYS_RAW_IO set, send SIGTERM instead (but it's unlikely that * we select a process with CAP_SYS_RAW_IO set). */ static void __oom_kill_task(task_t *p) { if (p->pid == 1) { WARN_ON(1); printk(KERN_WARNING "tried to kill init!\n"); return; } task_lock(p); if (!p->mm || p->mm == &init_mm) { WARN_ON(1); printk(KERN_WARNING "tried to kill an mm-less task!\n"); task_unlock(p); return; } task_unlock(p); printk(KERN_ERR "Out of Memory: Killed process %d (%s).\n", p->pid, p->comm); /* * We give our sacrificial lamb high priority and access to * all the memory it needs. That way it should be able to * exit() and clear out its resources quickly... */ p->time_slice = HZ; set_tsk_thread_flag(p, TIF_MEMDIE); force_sig(SIGKILL, p); } static struct mm_struct *oom_kill_task(task_t *p) { struct mm_struct *mm = get_task_mm(p); task_t * g, * q; if (!mm) return NULL; if (mm == &init_mm) { mmput(mm); return NULL; } __oom_kill_task(p); /* * kill all processes that share the ->mm (i.e. all threads), * but are in a different thread group */ do_each_thread(g, q) if (q->mm == mm && q->tgid != p->tgid) __oom_kill_task(q); while_each_thread(g, q); return mm; } static struct mm_struct *oom_kill_process(struct task_struct *p) { struct mm_struct *mm; struct task_struct *c; struct list_head *tsk; /* Try to kill a child first */ list_for_each(tsk, &p->children) { c = list_entry(tsk, struct task_struct, sibling); if (c->mm == p->mm) continue; mm = oom_kill_task(c); if (mm) return mm; } return oom_kill_task(p); } /** * oom_kill - kill the "best" process when we run out of memory * * If we run out of memory, we have the choice between either * killing a random task (bad), letting the system crash (worse) * OR try to be smart about which process to kill. Note that we * don't have to be perfect here, we just have to be good. */ void out_of_memory(unsigned int __nocast gfp_mask) { struct mm_struct *mm = NULL; task_t * p; printk("oom-killer: gfp_mask=0x%x\n", gfp_mask); /* print memory stats */ show_mem(); read_lock(&tasklist_lock); retry: p = select_bad_process(); if (PTR_ERR(p) == -1UL) goto out; /* Found nothing?!?! Either we hang forever, or we panic. */ if (!p) { read_unlock(&tasklist_lock); panic("Out of memory and no killable processes...\n"); } mm = oom_kill_process(p); if (!mm) goto retry; out: read_unlock(&tasklist_lock); if (mm) mmput(mm); /* * Give "p" a good chance of killing itself before we * retry to allocate memory. */ __set_current_state(TASK_INTERRUPTIBLE); schedule_timeout(1); }