lmkd/lmkd.c

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "lowmemorykiller"

#include <errno.h>
#include <inttypes.h>
#include <pwd.h>
#include <sched.h>
#include <signal.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>
#include <sys/cdefs.h>
#include <sys/epoll.h>
#include <sys/eventfd.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/sysinfo.h>
#include <sys/types.h>
#include <unistd.h>

#include <cutils/properties.h>
#include <cutils/sockets.h>
#include <lmkd.h>
#include <log/log.h>

#ifdef LMKD_LOG_STATS
#include <statslog.h>
#endif

/*
 * Define LMKD_TRACE_KILLS to record lmkd kills in kernel traces
 * to profile and correlate with OOM kills
 */
#ifdef LMKD_TRACE_KILLS

#define ATRACE_TAG ATRACE_TAG_ALWAYS
#include <cutils/trace.h>

#define TRACE_KILL_START(pid) ATRACE_INT(__FUNCTION__, pid);
#define TRACE_KILL_END()      ATRACE_INT(__FUNCTION__, 0);

#else /* LMKD_TRACE_KILLS */

#define TRACE_KILL_START(pid) ((void)(pid))
#define TRACE_KILL_END() ((void)0)

#endif /* LMKD_TRACE_KILLS */

#ifndef __unused
#define __unused __attribute__((__unused__))
#endif

#define MEMCG_SYSFS_PATH "/dev/memcg/"
#define MEMCG_MEMORY_USAGE "/dev/memcg/memory.usage_in_bytes"
#define MEMCG_MEMORYSW_USAGE "/dev/memcg/memory.memsw.usage_in_bytes"

#define LINE_MAX 128

#define INKERNEL_MINFREE_PATH "/sys/module/lowmemorykiller/parameters/minfree"
#define INKERNEL_ADJ_PATH "/sys/module/lowmemorykiller/parameters/adj"

#define ARRAY_SIZE(x)   (sizeof(x) / sizeof(*(x)))
#define EIGHT_MEGA (1 << 23)

/* Defined as ProcessList.SYSTEM_ADJ in ProcessList.java */
#define SYSTEM_ADJ (-900)

#define STRINGIFY(x) STRINGIFY_INTERNAL(x)
#define STRINGIFY_INTERNAL(x) #x

/* default to old in-kernel interface if no memory pressure events */
static bool use_inkernel_interface = true;
static bool has_inkernel_module;

/* memory pressure levels */
enum vmpressure_level {
    VMPRESS_LEVEL_LOW = 0,
    VMPRESS_LEVEL_MEDIUM,
    VMPRESS_LEVEL_CRITICAL,
    VMPRESS_LEVEL_COUNT
};

static const char *level_name[] = {
    "low",
    "medium",
    "critical"
};

struct mem_size {
    int free_mem;
    int free_swap;
};

struct {
    int min_free; /* recorded but not used yet */
    int max_free;
} low_pressure_mem = { -1, -1 };

static int level_oomadj[VMPRESS_LEVEL_COUNT];
static int mpevfd[VMPRESS_LEVEL_COUNT] = { -1, -1, -1 };
static bool debug_process_killing;
static bool enable_pressure_upgrade;
static int64_t upgrade_pressure;
static int64_t downgrade_pressure;
static bool low_ram_device;
static bool kill_heaviest_task;
static unsigned long kill_timeout_ms;

/* data required to handle events */
struct event_handler_info {
    int data;
    void (*handler)(int data, uint32_t events);
};

/* data required to handle socket events */
struct sock_event_handler_info {
    int sock;
    struct event_handler_info handler_info;
};

/* max supported number of data connections */
#define MAX_DATA_CONN 2

/* socket event handler data */
static struct sock_event_handler_info ctrl_sock;
static struct sock_event_handler_info data_sock[MAX_DATA_CONN];

/* vmpressure event handler data */
static struct event_handler_info vmpressure_hinfo[VMPRESS_LEVEL_COUNT];

/* 3 memory pressure levels, 1 ctrl listen socket, 2 ctrl data socket */
#define MAX_EPOLL_EVENTS (1 + MAX_DATA_CONN + VMPRESS_LEVEL_COUNT)
static int epollfd;
static int maxevents;

/* OOM score values used by both kernel and framework */
#define OOM_SCORE_ADJ_MIN       (-1000)
#define OOM_SCORE_ADJ_MAX       1000

static int lowmem_adj[MAX_TARGETS];
static int lowmem_minfree[MAX_TARGETS];
static int lowmem_targets_size;

struct sysmeminfo {
    int nr_free_pages;
    int nr_file_pages;
    int nr_shmem;
    int totalreserve_pages;
};

struct adjslot_list {
    struct adjslot_list *next;
    struct adjslot_list *prev;
};

struct proc {
    struct adjslot_list asl;
    int pid;
    uid_t uid;
    int oomadj;
    struct proc *pidhash_next;
};

struct reread_data {
    const char* const filename;
    int fd;
};

#ifdef LMKD_LOG_STATS
static bool enable_stats_log;
static android_log_context log_ctx;
#endif

#define PIDHASH_SZ 1024
static struct proc *pidhash[PIDHASH_SZ];
#define pid_hashfn(x) ((((x) >> 8) ^ (x)) & (PIDHASH_SZ - 1))

#define ADJTOSLOT(adj) ((adj) + -OOM_SCORE_ADJ_MIN)
static struct adjslot_list procadjslot_list[ADJTOSLOT(OOM_SCORE_ADJ_MAX) + 1];

/* PAGE_SIZE / 1024 */
static long page_k;

static bool parse_int64(const char* str, int64_t* ret) {
    char* endptr;
    long long val = strtoll(str, &endptr, 10);
    if (str == endptr || val > INT64_MAX) {
        return false;
    }
    *ret = (int64_t)val;
    return true;
}

/*
 * Read file content from the beginning up to max_len bytes or EOF
 * whichever happens first.
 */
static ssize_t read_all(int fd, char *buf, size_t max_len)
{
    ssize_t ret = 0;
    off_t offset = 0;

    while (max_len > 0) {
        ssize_t r = TEMP_FAILURE_RETRY(pread(fd, buf, max_len, offset));
        if (r == 0) {
            break;
        }
        if (r == -1) {
            return -1;
        }
        ret += r;
        buf += r;
        offset += r;
        max_len -= r;
    }

    return ret;
}

/*
 * Read a new or already opened file from the beginning.
 * If the file has not been opened yet data->fd should be set to -1.
 * To be used with files which are read often and possibly during high
 * memory pressure to minimize file opening which by itself requires kernel
 * memory allocation and might result in a stall on memory stressed system.
 */
static int reread_file(struct reread_data *data, char *buf, size_t buf_size) {
    ssize_t size;

    if (data->fd == -1) {
        data->fd = open(data->filename, O_RDONLY | O_CLOEXEC);
        if (data->fd == -1) {
            ALOGE("%s open: %s", data->filename, strerror(errno));
            return -1;
        }
    }

    size = read_all(data->fd, buf, buf_size - 1);
    if (size < 0) {
        ALOGE("%s read: %s", data->filename, strerror(errno));
        close(data->fd);
        data->fd = -1;
        return -1;
    }
    ALOG_ASSERT((size_t)size < buf_size - 1, data->filename " too large");
    buf[size] = 0;

    return 0;
}

static struct proc *pid_lookup(int pid) {
    struct proc *procp;

    for (procp = pidhash[pid_hashfn(pid)]; procp && procp->pid != pid;
         procp = procp->pidhash_next)
            ;

    return procp;
}

static void adjslot_insert(struct adjslot_list *head, struct adjslot_list *new)
{
    struct adjslot_list *next = head->next;
    new->prev = head;
    new->next = next;
    next->prev = new;
    head->next = new;
}

static void adjslot_remove(struct adjslot_list *old)
{
    struct adjslot_list *prev = old->prev;
    struct adjslot_list *next = old->next;
    next->prev = prev;
    prev->next = next;
}

static struct adjslot_list *adjslot_tail(struct adjslot_list *head) {
    struct adjslot_list *asl = head->prev;

    return asl == head ? NULL : asl;
}

static void proc_slot(struct proc *procp) {
    int adjslot = ADJTOSLOT(procp->oomadj);

    adjslot_insert(&procadjslot_list[adjslot], &procp->asl);
}

static void proc_unslot(struct proc *procp) {
    adjslot_remove(&procp->asl);
}

static void proc_insert(struct proc *procp) {
    int hval = pid_hashfn(procp->pid);

    procp->pidhash_next = pidhash[hval];
    pidhash[hval] = procp;
    proc_slot(procp);
}

static int pid_remove(int pid) {
    int hval = pid_hashfn(pid);
    struct proc *procp;
    struct proc *prevp;

    for (procp = pidhash[hval], prevp = NULL; procp && procp->pid != pid;
         procp = procp->pidhash_next)
            prevp = procp;

    if (!procp)
        return -1;

    if (!prevp)
        pidhash[hval] = procp->pidhash_next;
    else
        prevp->pidhash_next = procp->pidhash_next;

    proc_unslot(procp);
    free(procp);
    return 0;
}

/*
 * Write a string to a file.
 * Returns false if the file does not exist.
 */
static bool writefilestring(const char *path, const char *s,
                            bool err_if_missing) {
    int fd = open(path, O_WRONLY | O_CLOEXEC);
    ssize_t len = strlen(s);
    ssize_t ret;

    if (fd < 0) {
        if (err_if_missing) {
            ALOGE("Error opening %s; errno=%d", path, errno);
        }
        return false;
    }

    ret = TEMP_FAILURE_RETRY(write(fd, s, len));
    if (ret < 0) {
        ALOGE("Error writing %s; errno=%d", path, errno);
    } else if (ret < len) {
        ALOGE("Short write on %s; length=%zd", path, ret);
    }

    close(fd);
    return true;
}

static void cmd_procprio(LMKD_CTRL_PACKET packet) {
    struct proc *procp;
    char path[80];
    char val[20];
    int soft_limit_mult;
    struct lmk_procprio params;
    bool is_system_server;
    struct passwd *pwdrec;

    lmkd_pack_get_procprio(packet, &params);

    if (params.oomadj < OOM_SCORE_ADJ_MIN ||
        params.oomadj > OOM_SCORE_ADJ_MAX) {
        ALOGE("Invalid PROCPRIO oomadj argument %d", params.oomadj);
        return;
    }

    snprintf(path, sizeof(path), "/proc/%d/oom_score_adj", params.pid);
    snprintf(val, sizeof(val), "%d", params.oomadj);
    if (!writefilestring(path, val, false)) {
        ALOGW("Failed to open %s; errno=%d: process %d might have been killed",
              path, errno, params.pid);
        /* If this file does not exist the process is dead. */
        return;
    }

    if (use_inkernel_interface) {
        return;
    }

    if (params.oomadj >= 900) {
        soft_limit_mult = 0;
    } else if (params.oomadj >= 800) {
        soft_limit_mult = 0;
    } else if (params.oomadj >= 700) {
        soft_limit_mult = 0;
    } else if (params.oomadj >= 600) {
        // Launcher should be perceptible, don't kill it.
        params.oomadj = 200;
        soft_limit_mult = 1;
    } else if (params.oomadj >= 500) {
        soft_limit_mult = 0;
    } else if (params.oomadj >= 400) {
        soft_limit_mult = 0;
    } else if (params.oomadj >= 300) {
        soft_limit_mult = 1;
    } else if (params.oomadj >= 200) {
        soft_limit_mult = 2;
    } else if (params.oomadj >= 100) {
        soft_limit_mult = 10;
    } else if (params.oomadj >=   0) {
        soft_limit_mult = 20;
    } else {
        // Persistent processes will have a large
        // soft limit 512MB.
        soft_limit_mult = 64;
    }

    snprintf(path, sizeof(path),
             "/dev/memcg/apps/uid_%d/pid_%d/memory.soft_limit_in_bytes",
             params.uid, params.pid);
    snprintf(val, sizeof(val), "%d", soft_limit_mult * EIGHT_MEGA);

    /*
     * system_server process has no memcg under /dev/memcg/apps but should be
     * registered with lmkd. This is the best way so far to identify it.
     */
    is_system_server = (params.oomadj == SYSTEM_ADJ &&
                        (pwdrec = getpwnam("system")) != NULL &&
                        params.uid == pwdrec->pw_uid);
    writefilestring(path, val, !is_system_server);

    procp = pid_lookup(params.pid);
    if (!procp) {
            procp = malloc(sizeof(struct proc));
            if (!procp) {
                // Oh, the irony.  May need to rebuild our state.
                return;
            }

            procp->pid = params.pid;
            procp->uid = params.uid;
            procp->oomadj = params.oomadj;
            proc_insert(procp);
    } else {
        proc_unslot(procp);
        procp->oomadj = params.oomadj;
        proc_slot(procp);
    }
}

static void cmd_procremove(LMKD_CTRL_PACKET packet) {
    struct lmk_procremove params;

    if (use_inkernel_interface) {
        return;
    }

    lmkd_pack_get_procremove(packet, &params);
    pid_remove(params.pid);
}

static void cmd_target(int ntargets, LMKD_CTRL_PACKET packet) {
    int i;
    struct lmk_target target;

    if (ntargets > (int)ARRAY_SIZE(lowmem_adj))
        return;

    for (i = 0; i < ntargets; i++) {
        lmkd_pack_get_target(packet, i, &target);
        lowmem_minfree[i] = target.minfree;
        lowmem_adj[i] = target.oom_adj_score;
    }

    lowmem_targets_size = ntargets;

    if (has_inkernel_module) {
        char minfreestr[128];
        char killpriostr[128];

        minfreestr[0] = '\0';
        killpriostr[0] = '\0';

        for (i = 0; i < lowmem_targets_size; i++) {
            char val[40];

            if (i) {
                strlcat(minfreestr, ",", sizeof(minfreestr));
                strlcat(killpriostr, ",", sizeof(killpriostr));
            }

            snprintf(val, sizeof(val), "%d", use_inkernel_interface ? lowmem_minfree[i] : 0);
            strlcat(minfreestr, val, sizeof(minfreestr));
            snprintf(val, sizeof(val), "%d", use_inkernel_interface ? lowmem_adj[i] : 0);
            strlcat(killpriostr, val, sizeof(killpriostr));
        }

        writefilestring(INKERNEL_MINFREE_PATH, minfreestr, true);
        writefilestring(INKERNEL_ADJ_PATH, killpriostr, true);
    }
}

static void ctrl_data_close(int dsock_idx) {
    struct epoll_event epev;

    ALOGI("closing lmkd data connection");
    if (epoll_ctl(epollfd, EPOLL_CTL_DEL, data_sock[dsock_idx].sock, &epev) == -1) {
        // Log a warning and keep going
        ALOGW("epoll_ctl for data connection socket failed; errno=%d", errno);
    }
    maxevents--;

    close(data_sock[dsock_idx].sock);
    data_sock[dsock_idx].sock = -1;
}

static int ctrl_data_read(int dsock_idx, char *buf, size_t bufsz) {
    int ret = 0;

    ret = TEMP_FAILURE_RETRY(read(data_sock[dsock_idx].sock, buf, bufsz));

    if (ret == -1) {
        ALOGE("control data socket read failed; errno=%d", errno);
    } else if (ret == 0) {
        ALOGE("Got EOF on control data socket");
        ret = -1;
    }

    return ret;
}

static void ctrl_command_handler(int dsock_idx) {
    LMKD_CTRL_PACKET packet;
    int len;
    enum lmk_cmd cmd;
    int nargs;
    int targets;

    len = ctrl_data_read(dsock_idx, (char *)packet, CTRL_PACKET_MAX_SIZE);
    if (len <= 0)
        return;

    if (len < (int)sizeof(int)) {
        ALOGE("Wrong control socket read length len=%d", len);
        return;
    }

    cmd = lmkd_pack_get_cmd(packet);
    nargs = len / sizeof(int) - 1;
    if (nargs < 0)
        goto wronglen;

    switch(cmd) {
    case LMK_TARGET:
        targets = nargs / 2;
        if (nargs & 0x1 || targets > (int)ARRAY_SIZE(lowmem_adj))
            goto wronglen;
        cmd_target(targets, packet);
        break;
    case LMK_PROCPRIO:
        if (nargs != 3)
            goto wronglen;
        cmd_procprio(packet);
        break;
    case LMK_PROCREMOVE:
        if (nargs != 1)
            goto wronglen;
        cmd_procremove(packet);
        break;
    default:
        ALOGE("Received unknown command code %d", cmd);
        return;
    }

    return;

wronglen:
    ALOGE("Wrong control socket read length cmd=%d len=%d", cmd, len);
}

static void ctrl_data_handler(int data, uint32_t events) {
    if (events & EPOLLIN) {
        ctrl_command_handler(data);
    }
}

static int get_free_dsock() {
    for (int i = 0; i < MAX_DATA_CONN; i++) {
        if (data_sock[i].sock < 0) {
            return i;
        }
    }
    return -1;
}

static void ctrl_connect_handler(int data __unused, uint32_t events __unused) {
    struct epoll_event epev;
    int free_dscock_idx = get_free_dsock();

    if (free_dscock_idx < 0) {
        /*
         * Number of data connections exceeded max supported. This should not
         * happen but if it does we drop all existing connections and accept
         * the new one. This prevents inactive connections from monopolizing
         * data socket and if we drop ActivityManager connection it will
         * immediately reconnect.
         */
        for (int i = 0; i < MAX_DATA_CONN; i++) {
            ctrl_data_close(i);
        }
        free_dscock_idx = 0;
    }

    data_sock[free_dscock_idx].sock = accept(ctrl_sock.sock, NULL, NULL);
    if (data_sock[free_dscock_idx].sock < 0) {
        ALOGE("lmkd control socket accept failed; errno=%d", errno);
        return;
    }

    ALOGI("lmkd data connection established");
    /* use data to store data connection idx */
    data_sock[free_dscock_idx].handler_info.data = free_dscock_idx;
    data_sock[free_dscock_idx].handler_info.handler = ctrl_data_handler;
    epev.events = EPOLLIN;
    epev.data.ptr = (void *)&(data_sock[free_dscock_idx].handler_info);
    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, data_sock[free_dscock_idx].sock, &epev) == -1) {
        ALOGE("epoll_ctl for data connection socket failed; errno=%d", errno);
        ctrl_data_close(free_dscock_idx);
        return;
    }
    maxevents++;
}

#ifdef LMKD_LOG_STATS
static void memory_stat_parse_line(char *line, struct memory_stat *mem_st) {
    char key[LINE_MAX + 1];
    int64_t value;

    sscanf(line, "%" STRINGIFY(LINE_MAX) "s  %" SCNd64 "", key, &value);

    if (strcmp(key, "total_") < 0) {
        return;
    }

    if (!strcmp(key, "total_pgfault"))
        mem_st->pgfault = value;
    else if (!strcmp(key, "total_pgmajfault"))
        mem_st->pgmajfault = value;
    else if (!strcmp(key, "total_rss"))
        mem_st->rss_in_bytes = value;
    else if (!strcmp(key, "total_cache"))
        mem_st->cache_in_bytes = value;
    else if (!strcmp(key, "total_swap"))
        mem_st->swap_in_bytes = value;
}

static int memory_stat_parse(struct memory_stat *mem_st,  int pid, uid_t uid) {
   FILE *fp;
   char buf[PATH_MAX];

   snprintf(buf, sizeof(buf), MEMCG_PROCESS_MEMORY_STAT_PATH, uid, pid);

   fp = fopen(buf, "r");

   if (fp == NULL) {
       ALOGE("%s open failed: %s", buf, strerror(errno));
       return -1;
   }

   while (fgets(buf, PAGE_SIZE, fp) != NULL ) {
       memory_stat_parse_line(buf, mem_st);
   }
   fclose(fp);

   return 0;
}
#endif

static int get_free_memory(struct mem_size *ms) {
    struct sysinfo si;

    if (sysinfo(&si) < 0)
        return -1;

    ms->free_mem = (int)(si.freeram * si.mem_unit / PAGE_SIZE);
    ms->free_swap = (int)(si.freeswap * si.mem_unit / PAGE_SIZE);

    return 0;
}

static int proc_get_size(int pid) {
    char path[PATH_MAX];
    char line[LINE_MAX];
    int fd;
    int rss = 0;
    int total;
    ssize_t ret;

    snprintf(path, PATH_MAX, "/proc/%d/statm", pid);
    fd = open(path, O_RDONLY | O_CLOEXEC);
    if (fd == -1)
        return -1;

    ret = read_all(fd, line, sizeof(line) - 1);
    if (ret < 0) {
        close(fd);
        return -1;
    }

    sscanf(line, "%d %d ", &total, &rss);
    close(fd);
    return rss;
}

static char *proc_get_name(int pid) {
    char path[PATH_MAX];
    static char line[LINE_MAX];
    int fd;
    char *cp;
    ssize_t ret;

    snprintf(path, PATH_MAX, "/proc/%d/cmdline", pid);
    fd = open(path, O_RDONLY | O_CLOEXEC);
    if (fd == -1)
        return NULL;
    ret = read_all(fd, line, sizeof(line) - 1);
    close(fd);
    if (ret < 0) {
        return NULL;
    }

    cp = strchr(line, ' ');
    if (cp)
        *cp = '\0';

    return line;
}

static struct proc *proc_adj_lru(int oomadj) {
    return (struct proc *)adjslot_tail(&procadjslot_list[ADJTOSLOT(oomadj)]);
}

static struct proc *proc_get_heaviest(int oomadj) {
    struct adjslot_list *head = &procadjslot_list[ADJTOSLOT(oomadj)];
    struct adjslot_list *curr = head->next;
    struct proc *maxprocp = NULL;
    int maxsize = 0;
    while (curr != head) {
        int pid = ((struct proc *)curr)->pid;
        int tasksize = proc_get_size(pid);
        if (tasksize <= 0) {
            struct adjslot_list *next = curr->next;
            pid_remove(pid);
            curr = next;
        } else {
            if (tasksize > maxsize) {
                maxsize = tasksize;
                maxprocp = (struct proc *)curr;
            }
            curr = curr->next;
        }
    }
    return maxprocp;
}

/* Kill one process specified by procp.  Returns the size of the process killed */
static int kill_one_process(struct proc* procp, int min_score_adj,
                            enum vmpressure_level level) {
    int pid = procp->pid;
    uid_t uid = procp->uid;
    char *taskname;
    int tasksize;
    int r;

#ifdef LMKD_LOG_STATS
    struct memory_stat mem_st = {};
    int memory_stat_parse_result = -1;
#endif

    taskname = proc_get_name(pid);
    if (!taskname) {
        pid_remove(pid);
        return -1;
    }

    tasksize = proc_get_size(pid);
    if (tasksize <= 0) {
        pid_remove(pid);
        return -1;
    }

#ifdef LMKD_LOG_STATS
    if (enable_stats_log) {
        memory_stat_parse_result = memory_stat_parse(&mem_st, pid, uid);
    }
#endif

    TRACE_KILL_START(pid);

    r = kill(pid, SIGKILL);
    ALOGI(
        "Killing '%s' (%d), uid %d, adj %d\n"
        "   to free %ldkB because system is under %s memory pressure (min_oom_adj=%d)\n",
        taskname, pid, uid, procp->oomadj, tasksize * page_k,
        level_name[level], min_score_adj);
    pid_remove(pid);

    TRACE_KILL_END();

    if (r) {
        ALOGE("kill(%d): errno=%d", pid, errno);
        return -1;
    } else {
#ifdef LMKD_LOG_STATS
        if (memory_stat_parse_result == 0) {
            stats_write_lmk_kill_occurred(log_ctx, LMK_KILL_OCCURRED, uid, taskname,
                    procp->oomadj, mem_st.pgfault, mem_st.pgmajfault, mem_st.rss_in_bytes,
                    mem_st.cache_in_bytes, mem_st.swap_in_bytes);
        }
#endif
        return tasksize;
    }

    return tasksize;
}

/*
 * Find processes to kill to free required number of pages.
 * If pages_to_free is set to 0 only one process will be killed.
 * Returns the size of the killed processes.
 */
static int find_and_kill_processes(enum vmpressure_level level,
                                   int pages_to_free) {
    int i;
    int killed_size;
    int pages_freed = 0;
    int min_score_adj = level_oomadj[level];

#ifdef LMKD_LOG_STATS
    if (enable_stats_log) {
        stats_write_lmk_state_changed(log_ctx, LMK_STATE_CHANGED, LMK_STATE_CHANGE_START);
    }
#endif

    for (i = OOM_SCORE_ADJ_MAX; i >= min_score_adj; i--) {
        struct proc *procp;

        while (true) {
            procp = kill_heaviest_task ?
                proc_get_heaviest(i) : proc_adj_lru(i);

            if (!procp)
                break;

            killed_size = kill_one_process(procp, min_score_adj, level);
            if (killed_size >= 0) {
                pages_freed += killed_size;
                if (pages_freed >= pages_to_free) {

#ifdef LMKD_LOG_STATS
                    if (enable_stats_log) {
                        stats_write_lmk_state_changed(log_ctx, LMK_STATE_CHANGED,
                                LMK_STATE_CHANGE_STOP);
                    }
#endif
                    return pages_freed;
                }
            }
        }
    }

#ifdef LMKD_LOG_STATS
    if (enable_stats_log) {
        stats_write_lmk_state_changed(log_ctx, LMK_STATE_CHANGED, LMK_STATE_CHANGE_STOP);
    }
#endif

    return pages_freed;
}

static int64_t get_memory_usage(struct reread_data *file_data) {
    int ret;
    int64_t mem_usage;
    char buf[32];

    if (reread_file(file_data, buf, sizeof(buf)) < 0) {
        return -1;
    }

    if (!parse_int64(buf, &mem_usage)) {
        ALOGE("%s parse error", file_data->filename);
        return -1;
    }
    if (mem_usage == 0) {
        ALOGE("No memory!");
        return -1;
    }
    return mem_usage;
}

void record_low_pressure_levels(struct mem_size *free_mem) {
    if (low_pressure_mem.min_free == -1 ||
        low_pressure_mem.min_free > free_mem->free_mem) {
        if (debug_process_killing) {
            ALOGI("Low pressure min memory update from %d to %d",
                low_pressure_mem.min_free, free_mem->free_mem);
        }
        low_pressure_mem.min_free = free_mem->free_mem;
    }
    /*
     * Free memory at low vmpressure events occasionally gets spikes,
     * possibly a stale low vmpressure event with memory already
     * freed up (no memory pressure should have been reported).
     * Ignore large jumps in max_free that would mess up our stats.
     */
    if (low_pressure_mem.max_free == -1 ||
        (low_pressure_mem.max_free < free_mem->free_mem &&
         free_mem->free_mem - low_pressure_mem.max_free < low_pressure_mem.max_free * 0.1)) {
        if (debug_process_killing) {
            ALOGI("Low pressure max memory update from %d to %d",
                low_pressure_mem.max_free, free_mem->free_mem);
        }
        low_pressure_mem.max_free = free_mem->free_mem;
    }
}

enum vmpressure_level upgrade_level(enum vmpressure_level level) {
    return (enum vmpressure_level)((level < VMPRESS_LEVEL_CRITICAL) ?
        level + 1 : level);
}

enum vmpressure_level downgrade_level(enum vmpressure_level level) {
    return (enum vmpressure_level)((level > VMPRESS_LEVEL_LOW) ?
        level - 1 : level);
}

static inline unsigned long get_time_diff_ms(struct timeval *from,
                                             struct timeval *to) {
    return (to->tv_sec - from->tv_sec) * 1000 +
           (to->tv_usec - from->tv_usec) / 1000;
}

static void mp_event_common(int data, uint32_t events __unused) {
    int ret;
    unsigned long long evcount;
    int64_t mem_usage, memsw_usage;
    int64_t mem_pressure;
    enum vmpressure_level lvl;
    struct mem_size free_mem;
    static struct timeval last_report_tm;
    static unsigned long skip_count = 0;
    enum vmpressure_level level = (enum vmpressure_level)data;
    static struct reread_data mem_usage_file_data = {
        .filename = MEMCG_MEMORY_USAGE,
        .fd = -1,
    };
    static struct reread_data memsw_usage_file_data = {
        .filename = MEMCG_MEMORYSW_USAGE,
        .fd = -1,
    };

    /*
     * Check all event counters from low to critical
     * and upgrade to the highest priority one. By reading
     * eventfd we also reset the event counters.
     */
    for (lvl = VMPRESS_LEVEL_LOW; lvl < VMPRESS_LEVEL_COUNT; lvl++) {
        if (mpevfd[lvl] != -1 &&
            TEMP_FAILURE_RETRY(read(mpevfd[lvl],
                               &evcount, sizeof(evcount))) > 0 &&
            evcount > 0 && lvl > level) {
            level = lvl;
        }
    }

    if (kill_timeout_ms) {
        struct timeval curr_tm;
        gettimeofday(&curr_tm, NULL);
        if (get_time_diff_ms(&last_report_tm, &curr_tm) < kill_timeout_ms) {
            skip_count++;
            return;
        }
    }

    if (skip_count > 0) {
        if (debug_process_killing) {
            ALOGI("%lu memory pressure events were skipped after a kill!",
                skip_count);
        }
        skip_count = 0;
    }

    if (get_free_memory(&free_mem) == 0) {
        if (level == VMPRESS_LEVEL_LOW) {
            record_low_pressure_levels(&free_mem);
        }
    } else {
        ALOGE("Failed to get free memory!");
        return;
    }

    if (level_oomadj[level] > OOM_SCORE_ADJ_MAX) {
        /* Do not monitor this pressure level */
        return;
    }

    if ((mem_usage = get_memory_usage(&mem_usage_file_data)) < 0) {
        goto do_kill;
    }
    if ((memsw_usage = get_memory_usage(&memsw_usage_file_data)) < 0) {
        goto do_kill;
    }

    // Calculate percent for swappinness.
    mem_pressure = (mem_usage * 100) / memsw_usage;

    if (enable_pressure_upgrade && level != VMPRESS_LEVEL_CRITICAL) {
        // We are swapping too much.
        if (mem_pressure < upgrade_pressure) {
            level = upgrade_level(level);
            if (debug_process_killing) {
                ALOGI("Event upgraded to %s", level_name[level]);
            }
        }
    }

    // If the pressure is larger than downgrade_pressure lmk will not
    // kill any process, since enough memory is available.
    if (mem_pressure > downgrade_pressure) {
        if (debug_process_killing) {
            ALOGI("Ignore %s memory pressure", level_name[level]);
        }
        return;
    } else if (level == VMPRESS_LEVEL_CRITICAL &&
               mem_pressure > upgrade_pressure) {
        if (debug_process_killing) {
            ALOGI("Downgrade critical memory pressure");
        }
        // Downgrade event, since enough memory available.
        level = downgrade_level(level);
    }

do_kill:
    if (low_ram_device) {
        /* For Go devices kill only one task */
        if (find_and_kill_processes(level, 0) == 0) {
            if (debug_process_killing) {
                ALOGI("Nothing to kill");
            }
        }
    } else {
        /* If pressure level is less than critical and enough free swap then ignore */
        if (level < VMPRESS_LEVEL_CRITICAL && free_mem.free_swap > low_pressure_mem.max_free) {
            if (debug_process_killing) {
                ALOGI("Ignoring pressure since %d swap pages are available ", free_mem.free_swap);
            }
            return;
        }

        /* Free up enough memory to downgrate the memory pressure to low level */
        if (free_mem.free_mem < low_pressure_mem.max_free) {
            int pages_to_free = low_pressure_mem.max_free - free_mem.free_mem;
            if (debug_process_killing) {
                ALOGI("Trying to free %d pages", pages_to_free);
            }
            int pages_freed = find_and_kill_processes(level, pages_to_free);
            if (pages_freed < pages_to_free) {
                if (debug_process_killing) {
                    ALOGI("Unable to free enough memory (pages freed=%d)",
                        pages_freed);
                }
            } else {
                gettimeofday(&last_report_tm, NULL);
            }
        }
    }
}

static bool init_mp_common(enum vmpressure_level level) {
    int mpfd;
    int evfd;
    int evctlfd;
    char buf[256];
    struct epoll_event epev;
    int ret;
    int level_idx = (int)level;
    const char *levelstr = level_name[level_idx];

    mpfd = open(MEMCG_SYSFS_PATH "memory.pressure_level", O_RDONLY | O_CLOEXEC);
    if (mpfd < 0) {
        ALOGI("No kernel memory.pressure_level support (errno=%d)", errno);
        goto err_open_mpfd;
    }

    evctlfd = open(MEMCG_SYSFS_PATH "cgroup.event_control", O_WRONLY | O_CLOEXEC);
    if (evctlfd < 0) {
        ALOGI("No kernel memory cgroup event control (errno=%d)", errno);
        goto err_open_evctlfd;
    }

    evfd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
    if (evfd < 0) {
        ALOGE("eventfd failed for level %s; errno=%d", levelstr, errno);
        goto err_eventfd;
    }

    ret = snprintf(buf, sizeof(buf), "%d %d %s", evfd, mpfd, levelstr);
    if (ret >= (ssize_t)sizeof(buf)) {
        ALOGE("cgroup.event_control line overflow for level %s", levelstr);
        goto err;
    }

    ret = TEMP_FAILURE_RETRY(write(evctlfd, buf, strlen(buf) + 1));
    if (ret == -1) {
        ALOGE("cgroup.event_control write failed for level %s; errno=%d",
              levelstr, errno);
        goto err;
    }

    epev.events = EPOLLIN;
    /* use data to store event level */
    vmpressure_hinfo[level_idx].data = level_idx;
    vmpressure_hinfo[level_idx].handler = mp_event_common;
    epev.data.ptr = (void *)&vmpressure_hinfo[level_idx];
    ret = epoll_ctl(epollfd, EPOLL_CTL_ADD, evfd, &epev);
    if (ret == -1) {
        ALOGE("epoll_ctl for level %s failed; errno=%d", levelstr, errno);
        goto err;
    }
    maxevents++;
    mpevfd[level] = evfd;
    close(evctlfd);
    return true;

err:
    close(evfd);
err_eventfd:
    close(evctlfd);
err_open_evctlfd:
    close(mpfd);
err_open_mpfd:
    return false;
}

static int init(void) {
    struct epoll_event epev;
    int i;
    int ret;

    page_k = sysconf(_SC_PAGESIZE);
    if (page_k == -1)
        page_k = PAGE_SIZE;
    page_k /= 1024;

    epollfd = epoll_create(MAX_EPOLL_EVENTS);
    if (epollfd == -1) {
        ALOGE("epoll_create failed (errno=%d)", errno);
        return -1;
    }

    // mark data connections as not connected
    for (int i = 0; i < MAX_DATA_CONN; i++) {
        data_sock[i].sock = -1;
    }

    ctrl_sock.sock = android_get_control_socket("lmkd");
    if (ctrl_sock.sock < 0) {
        ALOGE("get lmkd control socket failed");
        return -1;
    }

    ret = listen(ctrl_sock.sock, MAX_DATA_CONN);
    if (ret < 0) {
        ALOGE("lmkd control socket listen failed (errno=%d)", errno);
        return -1;
    }

    epev.events = EPOLLIN;
    ctrl_sock.handler_info.handler = ctrl_connect_handler;
    epev.data.ptr = (void *)&(ctrl_sock.handler_info);
    if (epoll_ctl(epollfd, EPOLL_CTL_ADD, ctrl_sock.sock, &epev) == -1) {
        ALOGE("epoll_ctl for lmkd control socket failed (errno=%d)", errno);
        return -1;
    }
    maxevents++;

    has_inkernel_module = !access(INKERNEL_MINFREE_PATH, W_OK);
    use_inkernel_interface = has_inkernel_module;

    if (use_inkernel_interface) {
        ALOGI("Using in-kernel low memory killer interface");
    } else {
        if (!init_mp_common(VMPRESS_LEVEL_LOW) ||
            !init_mp_common(VMPRESS_LEVEL_MEDIUM) ||
            !init_mp_common(VMPRESS_LEVEL_CRITICAL)) {
            ALOGE("Kernel does not support memory pressure events or in-kernel low memory killer");
            return -1;
        }
    }

    for (i = 0; i <= ADJTOSLOT(OOM_SCORE_ADJ_MAX); i++) {
        procadjslot_list[i].next = &procadjslot_list[i];
        procadjslot_list[i].prev = &procadjslot_list[i];
    }

    return 0;
}

static void mainloop(void) {
    struct event_handler_info* handler_info;
    struct epoll_event *evt;

    while (1) {
        struct epoll_event events[maxevents];
        int nevents;
        int i;

        nevents = epoll_wait(epollfd, events, maxevents, -1);

        if (nevents == -1) {
            if (errno == EINTR)
                continue;
            ALOGE("epoll_wait failed (errno=%d)", errno);
            continue;
        }

        /*
         * First pass to see if any data socket connections were dropped.
         * Dropped connection should be handled before any other events
         * to deallocate data connection and correctly handle cases when
         * connection gets dropped and reestablished in the same epoll cycle.
         * In such cases it's essential to handle connection closures first.
         */
        for (i = 0, evt = &events[0]; i < nevents; ++i, evt++) {
            if ((evt->events & EPOLLHUP) && evt->data.ptr) {
                ALOGI("lmkd data connection dropped");
                handler_info = (struct event_handler_info*)evt->data.ptr;
                ctrl_data_close(handler_info->data);
            }
        }

        /* Second pass to handle all other events */
        for (i = 0, evt = &events[0]; i < nevents; ++i, evt++) {
            if (evt->events & EPOLLERR)
                ALOGD("EPOLLERR on event #%d", i);
            if (evt->events & EPOLLHUP) {
                /* This case was handled in the first pass */
                continue;
            }
            if (evt->data.ptr) {
                handler_info = (struct event_handler_info*)evt->data.ptr;
                handler_info->handler(handler_info->data, evt->events);
            }
        }
    }
}

int main(int argc __unused, char **argv __unused) {
    struct sched_param param = {
            .sched_priority = 1,
    };

    /* By default disable low level vmpressure events */
    level_oomadj[VMPRESS_LEVEL_LOW] =
        property_get_int32("ro.lmk.low", OOM_SCORE_ADJ_MAX + 1);
    level_oomadj[VMPRESS_LEVEL_MEDIUM] =
        property_get_int32("ro.lmk.medium", 800);
    level_oomadj[VMPRESS_LEVEL_CRITICAL] =
        property_get_int32("ro.lmk.critical", 0);
    debug_process_killing = property_get_bool("ro.lmk.debug", false);

    /* By default disable upgrade/downgrade logic */
    enable_pressure_upgrade =
        property_get_bool("ro.lmk.critical_upgrade", false);
    upgrade_pressure =
        (int64_t)property_get_int32("ro.lmk.upgrade_pressure", 100);
    downgrade_pressure =
        (int64_t)property_get_int32("ro.lmk.downgrade_pressure", 100);
    kill_heaviest_task =
        property_get_bool("ro.lmk.kill_heaviest_task", false);
    low_ram_device = property_get_bool("ro.config.low_ram", false);
    kill_timeout_ms =
        (unsigned long)property_get_int32("ro.lmk.kill_timeout_ms", 0);

#ifdef LMKD_LOG_STATS
    statslog_init(&log_ctx, &enable_stats_log);
#endif

    if (!init()) {
        if (!use_inkernel_interface) {
            /*
             * MCL_ONFAULT pins pages as they fault instead of loading
             * everything immediately all at once. (Which would be bad,
             * because as of this writing, we have a lot of mapped pages we
             * never use.) Old kernels will see MCL_ONFAULT and fail with
             * EINVAL; we ignore this failure.
             *
             * N.B. read the man page for mlockall. MCL_CURRENT | MCL_ONFAULT
             * pins ⊆ MCL_CURRENT, converging to just MCL_CURRENT as we fault
             * in pages.
             */
            if (mlockall(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT) && (errno != EINVAL)) {
                ALOGW("mlockall failed %s", strerror(errno));
            }

            sched_setscheduler(0, SCHED_FIFO, &param);
        }

        mainloop();
    }

#ifdef LMKD_LOG_STATS
    statslog_destroy(&log_ctx);
#endif

    ALOGI("exiting");
    return 0;
}