kernel 發 signal 通知 pid task_struct->comm

由 kernel space 找到 oom_test process name 之後透過 send_sig 通知 oom_test 這支process

user space

#include <stdio.h>
#include <stdlib.h>
#include <signal.h>

#define MEGABYTE 1024*1024


void signal_handler(int signum)
{
    printf("signal %d \n", signum);
    if (signum == SIGUSR2) {
        printf("oom_test SIGUSR2\n");
    } else if (signum == SIGUSR1) {
        printf("SIGUSR1\n");
    }
}

int main(int argc, char* argv[])
{
    void* myblock = NULL;
    int count = 0;
    signal(SIGUSR2, signal_handler);

    while (1) {
        myblock = (void*) malloc(MEGABYTE);

        if (!myblock) {
            break;
        }

        //sleep(1);

        memset(myblock, 1, MEGABYTE);
        printf("11 Currently allocating %d MB\n", ++count);
    }

    exit(0);
}

kernel space

• lowmemorykiller.c

/* drivers/misc/lowmemorykiller.c
 *
 * The lowmemorykiller driver lets user-space specify a set of memory thresholds
 * where processes with a range of oom_score_adj values will get killed. Specify
 * the minimum oom_score_adj values in
 * /sys/module/lowmemorykiller/parameters/adj and the number of free pages in
 * /sys/module/lowmemorykiller/parameters/minfree. Both files take a comma
 * separated list of numbers in ascending order.
 *
 * For example, write "0,8" to /sys/module/lowmemorykiller/parameters/adj and
 * "1024,4096" to /sys/module/lowmemorykiller/parameters/minfree to kill
 * processes with a oom_score_adj value of 8 or higher when the free memory
 * drops below 4096 pages and kill processes with a oom_score_adj value of 0 or
 * higher when the free memory drops below 1024 pages.
 *
 * The driver considers memory used for caches to be free, but if a large
 * percentage of the cached memory is locked this can be very inaccurate
 * and processes may not get killed until the normal oom killer is triggered.
 *
 * Copyright (C) 2007-2008 Google, Inc.
 *
 * This software is licensed under the terms of the GNU General Public
 * License version 2, as published by the Free Software Foundation, and
 * may be copied, distributed, and modified under those terms.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/oom.h>
#include <linux/sched.h>
#include <linux/swap.h>
#include <linux/rcupdate.h>
#include <linux/notifier.h>

int test_lowmemorykiller = 0;

static uint32_t lowmem_debug_level = 1;
static int lowmem_adj[6] = {
    0,
    1,
    6,
    12,
};
static int lowmem_adj_size = 4;
static int lowmem_minfree[6] = {
    3 * 512,	/* 6MB */
    2 * 1024,	/* 8MB */
    4 * 1024,	/* 16MB */
    16 * 1024,	/* 64MB */
};
static int lowmem_minfree_size = 4;

static unsigned long lowmem_deathpending_timeout;

#define lowmem_print(level, x...)			\
	do {						\
		if (lowmem_debug_level >= (level))	\
			pr_info(x);			\
	} while (0)

static int lowmem_shrink(struct shrinker *s, struct shrink_control *sc)
{
    struct task_struct *tsk;
    struct task_struct *selected = NULL;
    int rem = 0;
    int tasksize;
    int i;
    int min_score_adj = OOM_SCORE_ADJ_MAX + 1;
    int minfree = 0;
    int selected_tasksize = 0;
    int selected_oom_score_adj;
    int array_size = ARRAY_SIZE(lowmem_adj);
    int other_free = global_page_state(NR_FREE_PAGES) - totalreserve_pages;
    int other_file = global_page_state(NR_FILE_PAGES) -
                     global_page_state(NR_SHMEM);

    printk(KERN_CRIT "lowmem_shrink test_lowmemorykiller addr=%p\n", &test_lowmemorykiller);

    if (!strcmp(current->comm, "oom_test")) {
        printk(KERN_CRIT "lowmem_shrink oom_test+++++++++++++++++++++++++++++++++++++++++++++++");
        printk(KERN_CRIT "YAO lowmem_shrink PID=%d, PID name=%s\n", current->pid, current->comm);
        // dump_stack();
        for_each_process(tsk) {
            struct task_struct *p;

            p = find_lock_task_mm(tsk);

            if (!p)
                continue;

            if (strcmp("oom_test", p->comm) == 0) {
                send_sig(SIGUSR2, p, 0);
            }

            printk(KERN_CRIT "lowmem_shrink oom_test-----------------------------------------------");
        }
    }


    if (lowmem_adj_size < array_size)
        array_size = lowmem_adj_size;
    if (lowmem_minfree_size < array_size)
        array_size = lowmem_minfree_size;
    for (i = 0; i < array_size; i++) {
        minfree = lowmem_minfree[i];
        if (other_free < minfree && other_file < minfree) {
            min_score_adj = lowmem_adj[i];
            break;
        }
    }
    if (sc->nr_to_scan > 0)
        lowmem_print(3, "lowmem_shrink %lu, %x, ofree %d %d, ma %d\n",
                     sc->nr_to_scan, sc->gfp_mask, other_free,
                     other_file, min_score_adj);
    rem = global_page_state(NR_ACTIVE_ANON) +
          global_page_state(NR_ACTIVE_FILE) +
          global_page_state(NR_INACTIVE_ANON) +
          global_page_state(NR_INACTIVE_FILE);
    if (sc->nr_to_scan <= 0 || min_score_adj == OOM_SCORE_ADJ_MAX + 1) {
        lowmem_print(5, "lowmem_shrink %lu, %x, return %d\n",
                     sc->nr_to_scan, sc->gfp_mask, rem);
        return rem;
    }
    selected_oom_score_adj = min_score_adj;

    rcu_read_lock();
    for_each_process(tsk) {
        struct task_struct *p;
        int oom_score_adj;

        if (tsk->flags & PF_KTHREAD)
            continue;

        p = find_lock_task_mm(tsk);
        if (!p)
            continue;

        if (test_tsk_thread_flag(p, TIF_MEMDIE) &&
                time_before_eq(jiffies, lowmem_deathpending_timeout)) {
            task_unlock(p);
            rcu_read_unlock();
            return 0;
        }
        oom_score_adj = p->signal->oom_score_adj;
        if (oom_score_adj < min_score_adj) {
            task_unlock(p);
            continue;
        }
        tasksize = get_mm_rss(p->mm);
        task_unlock(p);
        if (tasksize <= 0)
            continue;
        if (selected) {
            if (oom_score_adj < selected_oom_score_adj)
                continue;
            if (oom_score_adj == selected_oom_score_adj &&
                    tasksize <= selected_tasksize)
                continue;
        }
        selected = p;
        selected_tasksize = tasksize;
        selected_oom_score_adj = oom_score_adj;
        lowmem_print(2, "select '%s' (%d), adj %d, size %d, to kill\n",
                     p->comm, p->pid, oom_score_adj, tasksize);
    }
    if (selected) {
        lowmem_print(1, "Killing '%s' (%d), adj %d,\n" \
                     "   to free %ldkB on behalf of '%s' (%d) because\n" \
                     "   cache %ldkB is below limit %ldkB for oom_score_adj %d\n" \
                     "   Free memory is %ldkB above reserved\n",
                     selected->comm, selected->pid,
                     selected_oom_score_adj,
                     selected_tasksize * (long)(PAGE_SIZE / 1024),
                     current->comm, current->pid,
                     other_file * (long)(PAGE_SIZE / 1024),
                     minfree * (long)(PAGE_SIZE / 1024),
                     min_score_adj,
                     other_free * (long)(PAGE_SIZE / 1024));
        lowmem_deathpending_timeout = jiffies + HZ;
        send_sig(SIGKILL, selected, 0);
        set_tsk_thread_flag(selected, TIF_MEMDIE);
        rem -= selected_tasksize;
    }
    lowmem_print(4, "lowmem_shrink %lu, %x, return %d\n",
                 sc->nr_to_scan, sc->gfp_mask, rem);
    rcu_read_unlock();
    return rem;
}

static struct shrinker lowmem_shrinker = {
    .shrink = lowmem_shrink,
    .seeks = DEFAULT_SEEKS * 16
};

static int __init lowmem_init(void)
{
    register_shrinker(&lowmem_shrinker);
    return 0;
}

static void __exit lowmem_exit(void)
{
    unregister_shrinker(&lowmem_shrinker);
}

#ifdef CONFIG_ANDROID_LOW_MEMORY_KILLER_AUTODETECT_OOM_ADJ_VALUES
static int lowmem_oom_adj_to_oom_score_adj(int oom_adj)
{
    if (oom_adj == OOM_ADJUST_MAX)
        return OOM_SCORE_ADJ_MAX;
    else
        return (oom_adj * OOM_SCORE_ADJ_MAX) / -OOM_DISABLE;
}

static void lowmem_autodetect_oom_adj_values(void)
{
    int i;
    int oom_adj;
    int oom_score_adj;
    int array_size = ARRAY_SIZE(lowmem_adj);

    if (lowmem_adj_size < array_size)
        array_size = lowmem_adj_size;

    if (array_size <= 0)
        return;

    oom_adj = lowmem_adj[array_size - 1];
    if (oom_adj > OOM_ADJUST_MAX)
        return;

    oom_score_adj = lowmem_oom_adj_to_oom_score_adj(oom_adj);
    if (oom_score_adj <= OOM_ADJUST_MAX)
        return;

    lowmem_print(1, "lowmem_shrink: convert oom_adj to oom_score_adj:\n");
    for (i = 0; i < array_size; i++) {
        oom_adj = lowmem_adj[i];
        oom_score_adj = lowmem_oom_adj_to_oom_score_adj(oom_adj);
        lowmem_adj[i] = oom_score_adj;
        lowmem_print(1, "oom_adj %d => oom_score_adj %d\n",
                     oom_adj, oom_score_adj);
    }
}

static int lowmem_adj_array_set(const char *val, const struct kernel_param *kp)
{
    int ret;

    ret = param_array_ops.set(val, kp);

    /* HACK: Autodetect oom_adj values in lowmem_adj array */
    lowmem_autodetect_oom_adj_values();

    return ret;
}

static int lowmem_adj_array_get(char *buffer, const struct kernel_param *kp)
{
    return param_array_ops.get(buffer, kp);
}

static void lowmem_adj_array_free(void *arg)
{
    param_array_ops.free(arg);
}

static struct kernel_param_ops lowmem_adj_array_ops = {
    .set = lowmem_adj_array_set,
    .get = lowmem_adj_array_get,
    .free = lowmem_adj_array_free,
};

static const struct kparam_array __param_arr_adj = {
    .max = ARRAY_SIZE(lowmem_adj),
    .num = &lowmem_adj_size,
    .ops = &param_ops_int,
    .elemsize = sizeof(lowmem_adj[0]),
    .elem = lowmem_adj,
};
#endif

module_param_named(cost, lowmem_shrinker.seeks, int, S_IRUGO | S_IWUSR);
#ifdef CONFIG_ANDROID_LOW_MEMORY_KILLER_AUTODETECT_OOM_ADJ_VALUES
__module_param_call(MODULE_PARAM_PREFIX, adj,
                    &lowmem_adj_array_ops,
                    .arr = &__param_arr_adj,
                    S_IRUGO | S_IWUSR, -1);
__MODULE_PARM_TYPE(adj, "array of int");
#else
module_param_array_named(adj, lowmem_adj, int, &lowmem_adj_size,
                         S_IRUGO | S_IWUSR);
#endif
module_param_array_named(minfree, lowmem_minfree, uint, &lowmem_minfree_size,
                         S_IRUGO | S_IWUSR);
module_param_named(debug_level, lowmem_debug_level, uint, S_IRUGO | S_IWUSR);

module_init(lowmem_init);
module_exit(lowmem_exit);

MODULE_LICENSE("GPL");

if (!strcmp(current->comm, "oom_test")) {
    printk(KERN_CRIT "lowmem_shrink oom_test+++++++++++++++++++++++++++++++++++++++++++++++");
    printk(KERN_CRIT "YAO lowmem_shrink PID=%d, PID name=%s\n", current->pid, current->comm);
    // dump_stack();
    for_each_process(tsk) {
        struct task_struct *p;

        p = find_lock_task_mm(tsk);

        if (!p)
            continue;

        if (strcmp("oom_test", p->comm) == 0) {
            send_sig(SIGUSR2, p, 0);
        }

        printk(KERN_CRIT "lowmem_shrink oom_test-----------------------------------------------");
    }
}
    ```