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DEFINITIONS
This source file includes following definitions.
- badness
- constrained_alloc
- select_bad_process
- dump_tasks
- __oom_kill_task
- oom_kill_task
- oom_kill_process
- mem_cgroup_out_of_memory
- register_oom_notifier
- unregister_oom_notifier
- try_set_zone_oom
- clear_zonelist_oom
- out_of_memory
/*
* 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/oom.h>
#include <linux/mm.h>
#include <linux/err.h>
#include <linux/sched.h>
#include <linux/swap.h>
#include <linux/timex.h>
#include <linux/jiffies.h>
#include <linux/cpuset.h>
#include <linux/module.h>
#include <linux/notifier.h>
#include <linux/memcontrol.h>
#include <linux/security.h>
int sysctl_panic_on_oom;
int sysctl_oom_kill_allocating_task;
int sysctl_oom_dump_tasks;
static DEFINE_SPINLOCK(zone_scan_mutex);
/* #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
* @mem: target memory controller
*
* 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);
/*
* swapoff can easily use up all memory, so kill those first.
*/
if (p->flags & PF_SWAPOFF)
return ULONG_MAX;
/*
* 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 (has_capability(p, CAP_SYS_ADMIN) ||
has_capability(p, CAP_SYS_RESOURCE))
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 (has_capability(p, CAP_SYS_RAWIO))
points /= 4;
/*
* If p's nodes don't overlap ours, it may still help to kill p
* because p may have allocated or otherwise mapped memory on
* this node before. However it will be less likely.
*/
if (!cpuset_mems_allowed_intersects(current, p))
points /= 8;
/*
* Adjust the score by oomkilladj.
*/
if (p->oomkilladj) {
if (p->oomkilladj > 0) {
if (!points)
points = 1;
points <<= p->oomkilladj;
} else
points >>= -(p->oomkilladj);
}
#ifdef DEBUG
printk(KERN_DEBUG "OOMkill: task %d (%s) got %lu points\n",
p->pid, p->comm, points);
#endif
return points;
}
/*
* Determine the type of allocation constraint.
*/
static inline enum oom_constraint constrained_alloc(struct zonelist *zonelist,
gfp_t gfp_mask)
{
#ifdef CONFIG_NUMA
struct zone *zone;
struct zoneref *z;
enum zone_type high_zoneidx = gfp_zone(gfp_mask);
nodemask_t nodes = node_states[N_HIGH_MEMORY];
for_each_zone_zonelist(zone, z, zonelist, high_zoneidx)
if (cpuset_zone_allowed_softwall(zone, gfp_mask))
node_clear(zone_to_nid(zone), 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 mem_cgroup *mem)
{
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;
/*
* skip kernel threads and tasks which have already released
* their mm.
*/
if (!p->mm)
continue;
/* skip the init task */
if (is_global_init(p))
continue;
if (mem && !task_in_mem_cgroup(p, mem))
continue;
/*
* This task already has access to memory reserves and is
* being killed. Don't allow any other task access to the
* memory reserve.
*
* Note: this may have a chance of deadlock if it gets
* blocked waiting for another task which itself is waiting
* for memory. Is there a better alternative?
*/
if (test_tsk_thread_flag(p, TIF_MEMDIE))
return ERR_PTR(-1UL);
/*
* This is in the process of releasing memory so wait for it
* to finish before killing some other task by mistake.
*
* However, if p is the current task, we allow the 'kill' to
* go ahead if it is exiting: this will simply set TIF_MEMDIE,
* which will allow it to gain access to memory reserves in
* the process of exiting and releasing its resources.
* Otherwise we could get an easy OOM deadlock.
*/
if (p->flags & PF_EXITING) {
if (p != current)
return ERR_PTR(-1UL);
chosen = p;
*ppoints = ULONG_MAX;
}
if (p->oomkilladj == OOM_DISABLE)
continue;
points = badness(p, uptime.tv_sec);
if (points > *ppoints || !chosen) {
chosen = p;
*ppoints = points;
}
} while_each_thread(g, p);
return chosen;
}
/**
* dump_tasks - dump current memory state of all system tasks
* @mem: target memory controller
*
* Dumps the current memory state of all system tasks, excluding kernel threads.
* State information includes task's pid, uid, tgid, vm size, rss, cpu, oom_adj
* score, and name.
*
* If the actual is non-NULL, only tasks that are a member of the mem_cgroup are
* shown.
*
* Call with tasklist_lock read-locked.
*/
static void dump_tasks(const struct mem_cgroup *mem)
{
struct task_struct *g, *p;
printk(KERN_INFO "[ pid ] uid tgid total_vm rss cpu oom_adj "
"name\n");
do_each_thread(g, p) {
/*
* total_vm and rss sizes do not exist for tasks with a
* detached mm so there's no need to report them.
*/
if (!p->mm)
continue;
if (mem && !task_in_mem_cgroup(p, mem))
continue;
task_lock(p);
printk(KERN_INFO "[%5d] %5d %5d %8lu %8lu %3d %3d %s\n",
p->pid, p->uid, p->tgid, p->mm->total_vm,
get_mm_rss(p->mm), (int)task_cpu(p), p->oomkilladj,
p->comm);
task_unlock(p);
} while_each_thread(g, p);
}
/*
* Send SIGKILL to the selected process irrespective of CAP_SYS_RAW_IO
* flag though it's unlikely that we select a process with CAP_SYS_RAW_IO
* set.
*/
static void __oom_kill_task(struct task_struct *p, int verbose)
{
if (is_global_init(p)) {
WARN_ON(1);
printk(KERN_WARNING "tried to kill init!\n");
return;
}
if (!p->mm) {
WARN_ON(1);
printk(KERN_WARNING "tried to kill an mm-less task!\n");
return;
}
if (verbose)
printk(KERN_ERR "Killed process %d (%s)\n",
task_pid_nr(p), 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->rt.time_slice = HZ;
set_tsk_thread_flag(p, TIF_MEMDIE);
force_sig(SIGKILL, p);
}
static int oom_kill_task(struct task_struct *p)
{
struct mm_struct *mm;
struct task_struct *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)
return 1;
/*
* Don't kill the process if any threads are set to OOM_DISABLE
*/
do_each_thread(g, q) {
if (q->mm == mm && q->oomkilladj == OOM_DISABLE)
return 1;
} while_each_thread(g, q);
__oom_kill_task(p, 1);
/*
* kill all processes that share the ->mm (i.e. all threads),
* but are in a different thread group. Don't let them have access
* to memory reserves though, otherwise we might deplete all memory.
*/
do_each_thread(g, q) {
if (q->mm == mm && !same_thread_group(q, p))
force_sig(SIGKILL, q);
} while_each_thread(g, q);
return 0;
}
static int oom_kill_process(struct task_struct *p, gfp_t gfp_mask, int order,
unsigned long points, struct mem_cgroup *mem,
const char *message)
{
struct task_struct *c;
if (printk_ratelimit()) {
printk(KERN_WARNING "%s invoked oom-killer: "
"gfp_mask=0x%x, order=%d, oomkilladj=%d\n",
current->comm, gfp_mask, order, current->oomkilladj);
dump_stack();
show_mem();
if (sysctl_oom_dump_tasks)
dump_tasks(mem);
}
/*
* If the task is already exiting, don't alarm the sysadmin or kill
* its children or threads, just set TIF_MEMDIE so it can die quickly
*/
if (p->flags & PF_EXITING) {
__oom_kill_task(p, 0);
return 0;
}
printk(KERN_ERR "%s: kill process %d (%s) score %li or a child\n",
message, task_pid_nr(p), p->comm, points);
/* Try to kill a child first */
list_for_each_entry(c, &p->children, sibling) {
if (c->mm == p->mm)
continue;
if (!oom_kill_task(c))
return 0;
}
return oom_kill_task(p);
}
#ifdef CONFIG_CGROUP_MEM_RES_CTLR
void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask)
{
unsigned long points = 0;
struct task_struct *p;
cgroup_lock();
read_lock(&tasklist_lock);
retry:
p = select_bad_process(&points, mem);
if (PTR_ERR(p) == -1UL)
goto out;
if (!p)
p = current;
if (oom_kill_process(p, gfp_mask, 0, points, mem,
"Memory cgroup out of memory"))
goto retry;
out:
read_unlock(&tasklist_lock);
cgroup_unlock();
}
#endif
static BLOCKING_NOTIFIER_HEAD(oom_notify_list);
int register_oom_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_register(&oom_notify_list, nb);
}
EXPORT_SYMBOL_GPL(register_oom_notifier);
int unregister_oom_notifier(struct notifier_block *nb)
{
return blocking_notifier_chain_unregister(&oom_notify_list, nb);
}
EXPORT_SYMBOL_GPL(unregister_oom_notifier);
/*
* Try to acquire the OOM killer lock for the zones in zonelist. Returns zero
* if a parallel OOM killing is already taking place that includes a zone in
* the zonelist. Otherwise, locks all zones in the zonelist and returns 1.
*/
int try_set_zone_oom(struct zonelist *zonelist, gfp_t gfp_mask)
{
struct zoneref *z;
struct zone *zone;
int ret = 1;
spin_lock(&zone_scan_mutex);
for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
if (zone_is_oom_locked(zone)) {
ret = 0;
goto out;
}
}
for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
/*
* Lock each zone in the zonelist under zone_scan_mutex so a
* parallel invocation of try_set_zone_oom() doesn't succeed
* when it shouldn't.
*/
zone_set_flag(zone, ZONE_OOM_LOCKED);
}
out:
spin_unlock(&zone_scan_mutex);
return ret;
}
/*
* Clears the ZONE_OOM_LOCKED flag for all zones in the zonelist so that failed
* allocation attempts with zonelists containing them may now recall the OOM
* killer, if necessary.
*/
void clear_zonelist_oom(struct zonelist *zonelist, gfp_t gfp_mask)
{
struct zoneref *z;
struct zone *zone;
spin_lock(&zone_scan_mutex);
for_each_zone_zonelist(zone, z, zonelist, gfp_zone(gfp_mask)) {
zone_clear_flag(zone, ZONE_OOM_LOCKED);
}
spin_unlock(&zone_scan_mutex);
}
/**
* out_of_memory - kill the "best" process when we run out of memory
* @zonelist: zonelist pointer
* @gfp_mask: memory allocation flags
* @order: amount of memory being requested as a power of 2
*
* 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)
{
struct task_struct *p;
unsigned long points = 0;
unsigned long freed = 0;
enum oom_constraint constraint;
blocking_notifier_call_chain(&oom_notify_list, 0, &freed);
if (freed > 0)
/* Got some memory back in the last second. */
return;
if (sysctl_panic_on_oom == 2)
panic("out of memory. Compulsory panic_on_oom is selected.\n");
/*
* Check if there were limitations on the allocation (only relevant for
* NUMA) that may require different handling.
*/
constraint = constrained_alloc(zonelist, gfp_mask);
read_lock(&tasklist_lock);
switch (constraint) {
case CONSTRAINT_MEMORY_POLICY:
oom_kill_process(current, gfp_mask, order, points, NULL,
"No available memory (MPOL_BIND)");
break;
case CONSTRAINT_NONE:
if (sysctl_panic_on_oom)
panic("out of memory. panic_on_oom is selected\n");
/* Fall-through */
case CONSTRAINT_CPUSET:
if (sysctl_oom_kill_allocating_task) {
oom_kill_process(current, gfp_mask, order, points, NULL,
"Out of memory (oom_kill_allocating_task)");
break;
}
retry:
/*
* Rambo mode: Shoot down a process and hope it solves whatever
* issues we may have.
*/
p = select_bad_process(&points, NULL);
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");
}
if (oom_kill_process(p, gfp_mask, order, points, NULL,
"Out of memory"))
goto retry;
break;
}
out:
read_unlock(&tasklist_lock);
/*
* 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);
}