oom_adj 值对应的进程优先级 : 优先级从上到下越来越高 , 最下面的优先级最高 , 最上面的优先级最低 ;
打印出来的值是上述值 , 不是常量中定义的值 ;
这些 ADJ 值都在 frameworks/base/services/core/java/com/android/server/am/ProcessList.java 源码中以常量形式记录 :
/**
* Activity manager code dealing with processes.
*/
public final class ProcessList {
// The B list of SERVICE_ADJ -- these are the old and decrepit
// services that aren't as shiny and interesting as the ones in the A list.
static final int SERVICE_B_ADJ = 800;
// This is the process of the previous application that the user was in.
// This process is kept above other things, because it is very common to
// switch back to the previous app. This is important both for recent
// task switch (toggling between the two top recent apps) as well as normal
// UI flow such as clicking on a URI in the e-mail app to view in the browser,
// and then pressing back to return to e-mail.
static final int PREVIOUS_APP_ADJ = 700;
// This is a process holding the home application -- we want to try
// avoiding killing it, even if it would normally be in the background,
// because the user interacts with it so much.
static final int HOME_APP_ADJ = 600;
// This is a process holding an application service -- killing it will not
// have much of an impact as far as the user is concerned.
static final int SERVICE_ADJ = 500;
// This is a process with a heavy-weight application. It is in the
// background, but we want to try to avoid killing it. Value set in
// system/rootdir/init.rc on startup.
static final int HEAVY_WEIGHT_APP_ADJ = 400;
// Adjustment used in certain places where we don't know it yet.
// (Generally this is something that is going to be cached, but we
// don't know the exact value in the cached range to assign yet.)
static final int UNKNOWN_ADJ = 1001;
// This is a process only hosting activities that are not visible,
// so it can be killed without any disruption.
static final int CACHED_APP_MAX_ADJ = 906;
static final int CACHED_APP_MIN_ADJ = 900;
// This is a process currently hosting a backup operation. Killing it
// is not entirely fatal but is generally a bad idea.
static final int BACKUP_APP_ADJ = 300;
// This is a process currently hosting a backup operation. Killing it
// is not entirely fatal but is generally a bad idea.
static final int BACKUP_APP_ADJ = 300;
// This is a process only hosting components that are perceptible to the
// user, and we really want to avoid killing them, but they are not
// immediately visible. An example is background music playback.
static final int PERCEPTIBLE_APP_ADJ = 200;
// This is a process only hosting activities that are visible to the
// user, so we'd prefer they don't disappear.
static final int VISIBLE_APP_ADJ = 100;
// This is the process running the current foreground app. We'd really
// rather not kill it!
static final int FOREGROUND_APP_ADJ = 0;
// This is a process that the system or a persistent process has bound to,
// and indicated it is important.
static final int PERSISTENT_SERVICE_ADJ = -700;
// This is a system persistent process, such as telephony. Definitely
// don't want to kill it, but doing so is not completely fatal.
static final int PERSISTENT_PROC_ADJ = -800;
// The system process runs at the default adjustment.
static final int SYSTEM_ADJ = -900;
// Special code for native processes that are not being managed by the system (so
// don't have an oom adj assigned by the system).
static final int NATIVE_ADJ = -1000;
// Memory pages are 4K.
static final int PAGE_SIZE = 4*1024;
}
参考源码 : frameworks/base/services/core/java/com/android/server/am/ProcessList.java
一个程序的 oom_adj 值是不断动态改变的 , 当程序处于前台时 , 该前台进程的 oom_adj 的值为 0 ,
运行程序 ,
在 Android Studio 中 , 可以看到该运行的程序的进程号 PID 为
,
进入 adb shell 命令行 , su 获取 root 权限 , 使用如下命令 , 查询指定 PID 的 oom_adj 值 ;
cat /proc/30856/oom_adj
点击 Home 键 , 程序退出 , 显示 Home 程序 ,
此时查询该 PID 为
的 oom_adj 值为
, 不可见进程范围是
~
, 此时的状态是不可见状态 ;
如果是按下回退键退出界面 , 此时查询该 PID 为
的 oom_adj 值为
, 此时进程的状态是缓存进程 , 随时都可能被杀掉 ;
优先级越高 , oom_adj 值越小 , 越不能被杀死 ;
如果想要使得进程尽可能长的保留在内存中 , 那么就要减小 oom_adj 的值 ;
在 oom_adj 值相同时 , 内存占用量越大的进程 , 被杀的几率就越高 , 因此这里还要尽可能降低进程占用尽可能少的内存 ;
总结一下就是 ① 降低 oom_adj 值 , ② 减小内存占用 ;