For Low-RAM Gadgets, Embrace Memory Cgroups

Starting March 27, 2025, we recommend utilizing android-latest-release as an alternative of aosp-main to build and contribute to AOSP. For more info, see Modifications to AOSP. Low memory killer daemon Keep organized with collections Save and categorize content material based on your preferences. The Android low memory killer daemon (lmkd) course of screens the memory state of a working Android system and reacts to excessive memory stress by killing the least important processes to keep the system performing at acceptable levels. An Android system running multiple processes in parallel could encounter situations when system memory is exhausted and processes that require more memory experience noticeable delays. Memory pressure, a state in which the system is running short on memory, requires Android to free Memory Wave (to alleviate the strain) by throttling or killing unimportant processes, requesting processes to free noncritical cached sources, and so on. Historically, Android monitored system Memory Wave Audio stress using an in-kernel low memory killer (LMK) driver, a rigid mechanism that will depend on laborious-coded values.

As of kernel 4.12, the LMK driver is removed from the upstream kernel and the userspace lmkd performs memory monitoring and process killing duties. Android 10 and better assist a new lmkd mode that uses kernel stress stall data (PSI) displays for memory strain detection. The PSI patchset within the upstream kernel (backported to 4.9 and 4.14 kernels) measures the period of time that tasks are delayed on account of memory shortages. As these delays immediately affect consumer expertise, they characterize a convenient metric for figuring out memory strain severity. The upstream kernel also consists of PSI monitors that permit privileged userspace processes (similar to lmkd) to specify thresholds for these delays and to subscribe to events from the kernel when a threshold is breached. As a result of the vmpressure indicators (generated by the kernel for memory strain detection and utilized by lmkd) often include numerous false positives, lmkd must perform filtering to determine if the memory is underneath actual strain.

This results in pointless lmkd wakeups and the use of further computational sources. Using PSI monitors outcomes in more correct memory strain detection and minimizes filtering overhead. The default is true, making PSI monitors the default mechanism of memory stress detection for lmkd. Low-RAM gadgets needed to be tuned aggressively, and even then would carry out poorly on workloads with massive file-backed lively pagecache. The poor efficiency resulted in thrashing and no kills. The LMK kernel driver relied on free-memory limits, with no scaling based mostly on the memory stress. Because of the rigidity of the design, companions typically personalized the driver in order that it could work on their gadgets. The LMK driver hooked into the slab shrinker API, which wasn't designed for heavy operations equivalent to searching for targets and killing them, which slowed down the vmscan process. The userspace lmkd implements the identical functionality because the in-kernel driver however uses existing kernel mechanisms to detect and estimate memory pressure. Such mechanisms embrace utilizing kernel-generated vmpressure events or pressure stall data (PSI) monitors to get notifications about memory pressure levels, and using memory cgroup options to restrict the memory resources allocated to each process primarily based on course of significance.

In Android 9 and better, userspace lmkd activates if an in-kernel LMK driver isn't detected. Userspace lmkd helps kill strategies primarily based on vmpressure occasions or PSI monitors, their severity, and different hints comparable to swap utilization. On low-memory gadgets, the system ought to tolerate higher memory strain as a traditional mode of operation. On high-efficiency gadgets, memory strain ought to be viewed as an abnormal scenario and mounted before it affects overall performance. Userspace lmkd additionally supports a legacy mode by which it makes kill decisions using the same strategies as the in-kernel LMK driver (that is, free memory and file cache thresholds). Configure lmkd for a specific gadget using the following properties. Android eleven improves the lmkd by introducing a new killing strategy. The killing technique uses a PSI mechanism for memory pressure detection launched in Android 10. lmkd in Android eleven accounts for memory useful resource use ranges and thrashing to forestall memory starvation and efficiency degradation. This killing technique replaces previous methods and can be utilized on both excessive-performance and low-RAM (Android Go) gadgets. For low-RAM devices, include memory cgroups. The memory killing strategy in Android 11 supports the tuning knobs and defaults listed under. These options work on each high-performance and low-RAM gadgets.