Android 11 QPR3 or higher supports the cached apps freezer. This feature stops execution for cached processes and reduces resource usage by misbehaving apps that might attempt to operate while cached. The framework freezes cached apps by migrating their processes into a frozen cgroup; this reduces active and idle CPU consumption in presence of active cached apps. The app freezer can be enabled using a system configuration flag or a developer option.
Implementing the apps freezer
The cached apps freezer leverages the kernel cgroup v2 freezer. Devices shipping
with a compatible kernel can (optionally) enable it. To do so, enable the
developer option "Suspend execution for cached apps" or set the device config
activity_manager_native_boot use_freezer to
true. For example:
adb shell device_config put activity_manager_native_boot use_freezer true && adb reboot
The freezer is disabled when the flag
use_freezer is set to false or the
developer option is disabled. You can toggle this setting by changing a device
configuration in a software release or update.
The apps freezer doesn't expose official APIs (and doesn't have a reference
implementation client), but does use the hidden system APIs
enableFreezer. For details on these APIs, refer to ActivityManager's
Process.java and the ActivityManagerService API. Developers can also refer to
the client code in
ActivityManager for experiments.
Handling custom features
Typically, processes aren't expected to do any work when cached, but some apps might have custom features supported by processes that are expected to run while cached. When the apps freezer is enabled on a device running such an app, the cached processes are frozen and might prevent custom features from working.
As a workaround, if an app has a process that needs to perform activities while cached, change the process status to non-cached (such as Bound ForeGround Service (BFGS) or foreground) before the process needs to do any work to allow the app to remain active.
Testing the apps freezer
To verify the app freezer is working as intended, use the following resources:
Check for a list of frozen processes using the
adb shell dumpsys activitycommand and grep the
Check for the presence of the
View logcat, which shows frozen/unfrozen entries each time a process migrates in or out of the freezer. For example:
adb logcat | grep -i "\(freezing\|froze\)"