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/*
* 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/swapctl.h>
#include <linux/timex.h>
/* #define DEBUG */
/**
* int_sqrt - oom_kill.c internal function, rough approximation to sqrt
* @x: integer of which to calculate the sqrt
*
* A very rough approximation to the sqrt() function.
*/
static unsigned int int_sqrt(unsigned int x)
{
unsigned int out = x;
while (x & ~(unsigned int)1) x >>=2, out >>=1;
if (x) out -= out >> 2;
return (out ? out : 1);
}
/**
* oom_badness - calculate a numeric value for how bad this task has been
* @p: task struct of which task we should calculate
*
* 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 priniciple
* of least surprise ... (be careful when you change it)
*/
static int badness(struct task_struct *p)
{
int points, cpu_time, run_time;
if (!p->mm)
return 0;
/*
* The memory size of the process is the basis for the badness.
*/
points = p->mm->total_vm;
/*
* CPU time is in seconds and run time is in minutes. There is no
* particular reason for this other than that it turned out to work
* very well in practice. This is not safe against jiffie wraps
* but we don't care _that_ much...
*/
cpu_time = (p->times.tms_utime + p->times.tms_stime) >> (SHIFT_HZ + 3);
run_time = (jiffies - p->start_time) >> (SHIFT_HZ + 10);
points /= int_sqrt(cpu_time);
points /= int_sqrt(int_sqrt(run_time));
/*
* Niced processes are most likely less important, so double
* their badness points.
*/
if (p->nice > 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;
#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 need the locks to make sure that the
* list of task structs doesn't change while we look the other way.
*
* (not docbooked, we don't want this one cluttering up the manual)
*/
static struct task_struct * select_bad_process(void)
{
int maxpoints = 0;
struct task_struct *p = NULL;
struct task_struct *chosen = NULL;
read_lock(&tasklist_lock);
for_each_task(p) {
if (p->pid) {
int points = badness(p);
if (points > maxpoints) {
chosen = p;
maxpoints = points;
}
}
}
read_unlock(&tasklist_lock);
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).
*/
void oom_kill_task(struct task_struct *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->counter = 5 * HZ;
p->flags |= PF_MEMALLOC | PF_MEMDIE;
/* This process has hardware access, be more careful. */
if (cap_t(p->cap_effective) & CAP_TO_MASK(CAP_SYS_RAWIO)) {
force_sig(SIGTERM, p);
} else {
force_sig(SIGKILL, 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.
*/
static void oom_kill(void)
{
struct task_struct *p = select_bad_process(), *q;
/* Found nothing?!?! Either we hang forever, or we panic. */
if (p == NULL)
panic("Out of memory and no killable processes...\n");
/* kill all processes that share the ->mm (i.e. all threads) */
read_lock(&tasklist_lock);
for_each_task(q) {
if(q->mm == p->mm) oom_kill_task(q);
}
read_unlock(&tasklist_lock);
/*
* Make kswapd go out of the way, so "p" has a good chance of
* killing itself before someone else gets the chance to ask
* for more memory.
*/
current->policy |= SCHED_YIELD;
schedule();
return;
}
/**
* out_of_memory - is the system out of memory?
*/
void out_of_memory(void)
{
static unsigned long first, last, count;
unsigned long now, since;
/*
* Enough swap space left? Not OOM.
*/
if (nr_swap_pages > 0)
return;
now = jiffies;
since = now - last;
last = now;
/*
* If it's been a long time since last failure,
* we're not oom.
*/
last = now;
if (since > 5*HZ)
goto reset;
/*
* If we haven't tried for at least one second,
* we're not really oom.
*/
since = now - first;
if (since < HZ)
return;
/*
* If we have gotten only a few failures,
* we're not really oom.
*/
if (++count < 10)
return;
/*
* Ok, really out of memory. Kill something.
*/
oom_kill();
reset:
first = now;
count = 0;
}
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