android app 不会被low memory killer回收

有一种方法可以设置app永远不会被kill，AndroidManifest.xml 中添加:
android:persistent="true"
适用于放在/system/app下的app

设置后app提升为系统核心级别，任何情况下不会被kill掉, settings->applications里面也会屏蔽掉stop操作,
设置前 Proc #19: adj=svc /B 4067b028 255:com.xxx.xxx/10001 (started-services)

# cat /proc/255/oom_adj
4

设置后 PERS #19: adj=core /F 406291f0 155:com.xxx.xxx/10001 (fixed)

# cat /proc/155/oom_adj
-12

lowmemorykiller的操作规则比如为

write /sys/module/lowmemorykiller/parameters/adj 0,1,2,4,7,15

write /sys/module/lowmemorykiller/parameters/minfree 2048,3072,4096,6144,7168,8192

可以看到，设置persistent后， oom_adj=-12，永远没有机会被lowmemorykiller处理

android:persistent

Whether or not the application should remain running at all times — "true" if it should, and "false" if not. The default value is "false". Applications should not normally set this flag; persistence mode is intended only for certain system applications

代码

[java] view
plaincopy

ActivityManagerService.java

final ProcessRecord addAppLocked(ApplicationInfo info) {

ProcessRecord app = getProcessRecordLocked(info.processName, info.uid);

if (app == null) {

app = newProcessRecordLocked(null, info, null);

mProcessNames.put(info.processName, info.uid, app);

updateLruProcessLocked(app, true, true);

}

if ((info.flags&(ApplicationInfo.FLAG_SYSTEM|ApplicationInfo.FLAG_PERSISTENT))

== (ApplicationInfo.FLAG_SYSTEM|ApplicationInfo.FLAG_PERSISTENT)) {

app.persistent = true;

app.maxAdj = CORE_SERVER_ADJ;

}

if (app.thread == null && mPersistentStartingProcesses.indexOf(app) < 0) {

mPersistentStartingProcesses.add(app);

startProcessLocked(app, "added application", app.processName);

}

return app;

}

可以看到同时符合FLAG_SYSTEM(/system/app目录)及FLAG_PERSISTENT(android:persistent="true")

的app，设置app.maxAdj = CORE_SERVER_ADJ(-12)，而adj=-12不会被lowmemorykiller处理