linux/mm/oom_kill.c
Dave Peterson 6937a25cff [PATCH] mm: fix typos in comments in mm/oom_kill.c
This fixes a few typos in the comments in mm/oom_kill.c.

Signed-off-by: David S. Peterson <dsp@llnl.gov>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-06-23 07:42:47 -07:00

383 lines
9.8 KiB
C

/*
* 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>
#include <linux/cpuset.h>
int sysctl_panic_on_oom;
/* #define DEBUG */
/**
* 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 mm_struct *mm;
struct task_struct *child;
task_lock(p);
mm = p->mm;
if (!mm) {
task_unlock(p);
return 0;
}
/*
* The memory size of the process is the basis for the badness.
*/
points = mm->total_vm;
/*
* After this unlock we can no longer dereference local variable `mm'
*/
task_unlock(p);
/*
* Processes which fork a lot of child processes are likely
* a good choice. We add half 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. In case a single
* child is eating the vast majority of memory, adding only half
* to the parents will make the child our kill candidate of choice.
*/
list_for_each_entry(child, &p->children, sibling) {
task_lock(child);
if (child->mm != mm && child->mm)
points += child->mm->total_vm/2 + 1;
task_unlock(child);
}
/*
* 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;
}
/*
* Types of limitations to the nodes from which allocations may occur
*/
#define CONSTRAINT_NONE 1
#define CONSTRAINT_MEMORY_POLICY 2
#define CONSTRAINT_CPUSET 3
/*
* Determine the type of allocation constraint.
*/
static inline int constrained_alloc(struct zonelist *zonelist, gfp_t gfp_mask)
{
#ifdef CONFIG_NUMA
struct zone **z;
nodemask_t nodes = node_online_map;
for (z = zonelist->zones; *z; z++)
if (cpuset_zone_allowed(*z, gfp_mask))
node_clear((*z)->zone_pgdat->node_id,
nodes);
else
return CONSTRAINT_CPUSET;
if (!nodes_empty(nodes))
return CONSTRAINT_MEMORY_POLICY;
#endif
return CONSTRAINT_NONE;
}
/*
* 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(unsigned long *ppoints)
{
struct task_struct *g, *p;
struct task_struct *chosen = NULL;
struct timespec uptime;
*ppoints = 0;
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;
/* If p's nodes don't overlap ours, it won't help to kill p. */
if (!cpuset_excl_nodes_overlap(p))
continue;
/*
* This is in the process of releasing memory so wait for 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 > *ppoints || !chosen) {
chosen = p;
*ppoints = 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, const char *message)
{
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 "%s: Killed process %d (%s).\n",
message, 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 int oom_kill_task(task_t *p, const char *message)
{
struct mm_struct *mm;
task_t * g, * q;
mm = p->mm;
/* WARNING: mm may not be dereferenced since we did not obtain its
* value from get_task_mm(p). This is OK since all we need to do is
* compare mm to q->mm below.
*
* Furthermore, even if mm contains a non-NULL value, p->mm may
* change to NULL at any time since we do not hold task_lock(p).
* However, this is of no concern to us.
*/
if (mm == NULL || mm == &init_mm)
return 1;
__oom_kill_task(p, message);
/*
* 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, message);
while_each_thread(g, q);
return 0;
}
static int oom_kill_process(struct task_struct *p, unsigned long points,
const char *message)
{
struct task_struct *c;
struct list_head *tsk;
printk(KERN_ERR "Out of Memory: Kill process %d (%s) score %li and "
"children.\n", p->pid, p->comm, points);
/* 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;
if (!oom_kill_task(c, message))
return 0;
}
return oom_kill_task(p, message);
}
/**
* out_of_memory - 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(struct zonelist *zonelist, gfp_t gfp_mask, int order)
{
task_t *p;
unsigned long points = 0;
if (printk_ratelimit()) {
printk("oom-killer: gfp_mask=0x%x, order=%d\n",
gfp_mask, order);
dump_stack();
show_mem();
}
cpuset_lock();
read_lock(&tasklist_lock);
/*
* Check if there were limitations on the allocation (only relevant for
* NUMA) that may require different handling.
*/
switch (constrained_alloc(zonelist, gfp_mask)) {
case CONSTRAINT_MEMORY_POLICY:
oom_kill_process(current, points,
"No available memory (MPOL_BIND)");
break;
case CONSTRAINT_CPUSET:
oom_kill_process(current, points,
"No available memory in cpuset");
break;
case CONSTRAINT_NONE:
if (sysctl_panic_on_oom)
panic("out of memory. panic_on_oom is selected\n");
retry:
/*
* Rambo mode: Shoot down a process and hope it solves whatever
* issues we may have.
*/
p = select_bad_process(&points);
if (PTR_ERR(p) == -1UL)
goto out;
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!p) {
read_unlock(&tasklist_lock);
cpuset_unlock();
panic("Out of memory and no killable processes...\n");
}
if (oom_kill_process(p, points, "Out of memory"))
goto retry;
break;
}
out:
read_unlock(&tasklist_lock);
cpuset_unlock();
/*
* Give "p" a good chance of killing itself before we
* retry to allocate memory unless "p" is current
*/
if (!test_thread_flag(TIF_MEMDIE))
schedule_timeout_uninterruptible(1);
}