psi機制

#define PSI_PATH_MEMORY "/proc/pressure/memory"
#define PSI_PATH_IO "/proc/pressure/io"
#define PSI_PATH_CPU    "/proc/pressure/cpu"

PSI會注冊三個壓力監(jiān)測器诅岩，如果內(nèi)存壓力太大，就會回調(diào)lmkd函數(shù)進行查殺。

lowmemory監(jiān)測

frameworks/base/services/core/jni/com_android_server_am_LowMemDetector.cpp

static jint android_server_am_LowMemDetector_init(JNIEnv*, jobject) {
    int epollfd;
    int low_psi_fd;
    int medium_psi_fd;
    int high_psi_fd;

    epollfd = epoll_create(PRESSURE_LEVEL_COUNT);
    if (epollfd == -1) {
        ALOGE("epoll_create failed: %s", strerror(errno));
        return -1;
    }

    low_psi_fd = init_psi_monitor(PSI_SOME, PSI_LOW_STALL_US, PSI_WINDOW_SIZE_US);
    if (low_psi_fd < 0 ||
        register_psi_monitor(epollfd, low_psi_fd, (void*)PRESSURE_LOW) != 0) {
        goto low_fail;
    }
---分割線---
[ams構(gòu)造函數(shù)]
        mAppProfiler = new AppProfiler(this, BackgroundThread.getHandler().getLooper(),
                new LowMemDetector(this));
[LowMemDetector.init]
private native int init();

---分割線---
[frameworks/base/services/core/jni/com_android_server_am_LowMemDetector.cpp]
static const JNINativeMethod sMethods[] = {
    /* name, signature, funcPtr */
    {"init", "()I", (void*)android_server_am_LowMemDetector_init},
    {"waitForPressure", "()I",
     (void*)android_server_am_LowMemDetector_waitForPressure},
};

ProcessList-lmkd

    // Low Memory Killer Daemon command codes.
    // These must be kept in sync with lmk_cmd definitions in lmkd.h
    //
    // LMK_TARGET <minfree> <minkillprio> ... (up to 6 pairs)
    // LMK_PROCPRIO <pid> <uid> <prio>
    // LMK_PROCREMOVE <pid>
    // LMK_PROCPURGE
    // LMK_GETKILLCNT
    // LMK_SUBSCRIBE
    // LMK_PROCKILL
    // LMK_UPDATE_PROPS
    // LMK_KILL_OCCURRED
    // LMK_STATE_CHANGED
    static final byte LMK_TARGET = 0;
    static final byte LMK_PROCPRIO = 1;
    static final byte LMK_PROCREMOVE = 2;
    static final byte LMK_PROCPURGE = 3;
    static final byte LMK_GETKILLCNT = 4;
    static final byte LMK_SUBSCRIBE = 5;
    static final byte LMK_PROCKILL = 6; // Note: this is an unsolicited command
    static final byte LMK_UPDATE_PROPS = 7;
    static final byte LMK_KILL_OCCURRED = 8; // Msg to subscribed clients on kill occurred event
    static final byte LMK_STATE_CHANGED = 9; // Msg to subscribed clients on state changed

    // Low Memory Killer Daemon command codes.
    // These must be kept in sync with async_event_type definitions in lmkd.h
    //
    static final int LMK_ASYNC_EVENT_KILL = 0;
    static final int LMK_ASYNC_EVENT_STAT = 1;

    // lmkd reconnect delay in msecs
    private static final long LMKD_RECONNECT_DELAY_MS = 1000;

將oomadj寫入lmkd模塊

processList向lmkd寫入進程對應(yīng)的oomadj

    public static void setOomAdj(int pid, int uid, int amt) {
        // This indicates that the process is not started yet and so no need to proceed further.
        if (pid <= 0) {
            return;
        }
        if (amt == UNKNOWN_ADJ)
            return;

        long start = SystemClock.elapsedRealtime();
        ByteBuffer buf = ByteBuffer.allocate(4 * 4);
//這里傳遞標記位意思是更新proc的oomadj
        buf.putInt(LMK_PROCPRIO);
        buf.putInt(pid);
        buf.putInt(uid);
        buf.putInt(amt);
//通過socket向lmkd發(fā)消息
        writeLmkd(buf, null);
        long now = SystemClock.elapsedRealtime();
        if ((now-start) > 250) {
            Slog.w("ActivityManager", "SLOW OOM ADJ: " + (now-start) + "ms for pid " + pid
                    + " = " + amt);
        }
    }

• 向lmkd發(fā)消息更新proc的oomadj

lmkd通過socket接收消息

static void cmd_procprio(LMKD_CTRL_PACKET packet, int field_count, struct ucred *cred) {
// 。廷臼。。省略
snprintf(path, sizeof(path), "/proc/%d/oom_score_adj", params.pid);

---分割線
console:/proc/552 # cat oom_score_adj
-900