/*
* 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 __alloc_pages()
* in mm/page_alloc.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
* @uptime: 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 children if they
* have an own mm. This prevents forking servers to flood the
* machine with an endless amount of children
*/
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) {
unsigned long points;
int releasing;
/* skip the init task with pid == 1 */
if (p->pid == 1)
continue;
if (p->oomkilladj == OOM_DISABLE)
continue;
/*
* This is in the process of releasing memory so for wait it
* to finish before killing some other task by mistake.
*/
releasing = test_tsk_thread_flag(p, TIF_MEMDIE) ||
p->flags & PF_EXITING;
if (releasing && !(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, int order)
{
struct mm_struct *mm = NULL;
task_t * p;
if (printk_ratelimit()) {
printk("oom-killer: gfp_mask=0x%x, order=%d\n",
gfp_mask, order);
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);
}
