I've made a draft version of the out-of-memory
killer (linux/mm/oom_kill.c) but it isn't complete
yet and could probably be better.
Especially the IOPL/IOPERM stuff is very important
but I haven't figured it out yet :(
Also, there's no code yet to trigger this routine,
so everybody should be safe for now :)
(I post this mainly because we've had several flamewars
over this issue and I want to prevent that this time)
Rik.
+-------------------------------------------+--------------------------+
| Linux: - LinuxHQ MM-patches page | Scouting webmaster |
| - kswapd ask-him & complain-to guy | Vries cubscout leader |
| http://www.phys.uu.nl/~riel/ | <H.H.vanRiel@phys.uu.nl> |
+-------------------------------------------+--------------------------+
/*
* linux/mm/oom_kill.c
*
* Copyright (C) 1998 Rik van Riel
*
* 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 the pageout daemon gets stuck.
*
* We hope to call this function as little as often, there are
* no critical code paths in here. Don't try to be smart, just
* leave it ultra-readable so we'll never mess up...
*/
#include <linux/sched.h>
#define DEBUG
/* Ugly helper function, we don't want to do without it because
* the points variable might overflow if we just squared the
* size instead. */
inline int int_sqrt(int x)
{
int i,out;
for (i = 10; i-- > 0;)
out = x + out >> 1;
if (out)
return out;
return 1;
}
inline int badness(task_struct *p)
{
int points = p->mm->total_vm;
points /= int_sqrt((p->tms->tms_utime + p->tms->tms_stime) >> (SHIFT_HZ + 6))
if (p->priority < DEF_PRIORITY)
points <<= 1;
if (p->uid == 0 || p->euid == 0)
points >>= 1;
/* FIXME: - strange assumption being made :)
* - not jiffie-overflow safe! */
if (p->start_time < jiffies >> 6)
points >>= 1;
/* FIXME: How can I test for IOPL or IOPERM permissions??? */
if (/* p->tss-> || */ p->cap_effective & CAP_SYS_RAWIO)
points = 0;
#ifdef DEBUG
printk(KERN_DEBUG "OOMkill: task %d (%s) got %d points\n",
p->pid, p->comm, points);
#endif
}
inline struct task_struct * select_bad_process(void)
{
int points = 0;
struct task_struct *p = NULL;
struct task_struct *chosen = NULL;
read_lock(&tasklist_lock); /* We might need this on SMP */
for_each_task(p)
if (p->pid && badness(p) > points)
chosen = p;
read_unlock(&tasklist_lock);
return chosen;
}
/*
* The SCHED_FIFO magic is because we want the process to
* be able to kill itself even when kswapd is running.
*/
void oom_kill(void)
{
struct task_struct *p = select_bad_process();
if (p == NULL)
return;
force_sig(SIGKILL, p);
p->policy = SCHED_FIFO;
p->rt_priority = 1000;
current->policy |= SCHED_YIELD;
schedule();
}
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