/* drivers/misc/lowmemorykiller.c
 *
 * The lowmemorykiller driver lets user-space specify a set of memory thresholds
 * where processes with a range of oom_adj values will get killed. Specify the
 * minimum oom_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_adj value of 8 or higher when the free memory drops below 4096 pages
 * and kill processes with a oom_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.
 *
 */

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

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

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

static int lowmem_shrink(int nr_to_scan, gfp_t gfp_mask)
{
	struct task_struct *p;
	struct task_struct *selected = NULL;
	int rem = 0;
	int tasksize;
	int i;
	int min_adj = OOM_ADJUST_MAX + 1;
	int selected_tasksize = 0;
	int selected_oom_adj;
	int array_size = ARRAY_SIZE(lowmem_adj);
	int other_free = global_page_state(NR_FREE_PAGES);
	int other_file = global_page_state(NR_FILE_PAGES);

	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++) {
		if (other_free < lowmem_minfree[i] &&
		    other_file < lowmem_minfree[i]) {
			min_adj = lowmem_adj[i];
			break;
		}
	}
	if (nr_to_scan > 0)
		lowmem_print(3, "lowmem_shrink %d, %x, ofree %d %d, ma %d\n",
			     nr_to_scan, gfp_mask, other_free, other_file,
			     min_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 (nr_to_scan <= 0 || min_adj == OOM_ADJUST_MAX + 1) {
		lowmem_print(5, "lowmem_shrink %d, %x, return %d\n",
			     nr_to_scan, gfp_mask, rem);
		return rem;
	}
	selected_oom_adj = min_adj;

	read_lock(&tasklist_lock);
	for_each_process(p) {
		struct mm_struct *mm;
		int oom_adj;

		task_lock(p);
		mm = p->mm;
		if (!mm) {
			task_unlock(p);
			continue;
		}
		oom_adj = mm->oom_adj;
		if (oom_adj < min_adj) {
			task_unlock(p);
			continue;
		}
		tasksize = get_mm_rss(mm);
		task_unlock(p);
		if (tasksize <= 0)
			continue;
		if (selected) {
			if (oom_adj < selected_oom_adj)
				continue;
			if (oom_adj == selected_oom_adj &&
			    tasksize <= selected_tasksize)
				continue;
		}
		selected = p;
		selected_tasksize = tasksize;
		selected_oom_adj = oom_adj;
		lowmem_print(2, "select %d (%s), adj %d, size %d, to kill\n",
			     p->pid, p->comm, oom_adj, tasksize);
	}
	if (selected) {
		lowmem_print(1, "send sigkill to %d (%s), adj %d, size %d\n",
			     selected->pid, selected->comm,
			     selected_oom_adj, selected_tasksize);
		force_sig(SIGKILL, selected);
		rem -= selected_tasksize;
	}
	lowmem_print(4, "lowmem_shrink %d, %x, return %d\n",
		     nr_to_scan, gfp_mask, rem);
	read_unlock(&tasklist_lock);
	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);
}

module_param_named(cost, lowmem_shrinker.seeks, int, S_IRUGO | S_IWUSR);
module_param_array_named(adj, lowmem_adj, int, &lowmem_adj_size,
			 S_IRUGO | S_IWUSR);
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");