/*
 *  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>

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,
                        struct mem_cgroup *mem)
{
        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 (__capable(p, CAP_SYS_ADMIN) || __capable(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 (__capable(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 **z;
        nodemask_t nodes = node_states[N_HIGH_MEMORY];

        for (z = zonelist->zones; *z; z++)
                if (cpuset_zone_allowed_softwall(*z, gfp_mask))
                        node_clear(zone_to_nid(*z), 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, mem);
                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)
{
        struct zone **z;
        int ret = 1;

        z = zonelist->zones;

        spin_lock(&zone_scan_mutex);
        do {
                if (zone_is_oom_locked(*z)) {
                        ret = 0;
                        goto out;
                }
        } while (*(++z) != NULL);

        /*
         * 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.
         */
        z = zonelist->zones;
        do {
                zone_set_flag(*z, ZONE_OOM_LOCKED);
        } while (*(++z) != NULL);
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)
{
        struct zone **z;

        z = zonelist->zones;

        spin_lock(&zone_scan_mutex);
        do {
                zone_clear_flag(*z, ZONE_OOM_LOCKED);
        } while (*(++z) != NULL);
        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);
}