Starting March 27, 2025, we recommend using android-latest-launch as an alternative of aosp-essential to build and contribute to AOSP. For Memory Wave extra information, see Adjustments to AOSP. Low memory killer daemon Keep organized with collections Save and categorize content material primarily based in your preferences. The Android low memory killer daemon (lmkd) process screens the memory state of a working Android system and reacts to high memory pressure by killing the least important processes to keep the system performing at acceptable levels. An Android system operating a number of processes in parallel could encounter situations when system memory is exhausted and processes that require extra memory experience noticeable delays. Memory strain, a state in which the system is running quick on memory, requires Android to free memory (to alleviate the pressure) by throttling or killing unimportant processes, requesting processes to free noncritical cached assets, and so forth. Historically, Android monitored system memory stress using an in-kernel low memory killer (LMK) driver, a inflexible mechanism that is dependent upon 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 tasks. Android 10 and higher assist a new lmkd mode that uses kernel strain stall data (PSI) screens for memory stress 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 because of memory shortages. As these delays instantly affect user experience, they symbolize a handy metric for determining memory stress severity. The upstream kernel additionally consists of PSI screens that allow privileged userspace processes (equivalent to lmkd) to specify thresholds for these delays and to subscribe to occasions from the kernel when a threshold is breached. Because the vmpressure indicators (generated by the kernel for memory stress detection and utilized by lmkd) typically embrace numerous false positives, lmkd should carry out filtering to find out if the memory is below real strain.

This results in unnecessary lmkd wakeups and the usage of extra computational resources. Utilizing PSI monitors outcomes in additional accurate memory strain detection and minimizes filtering overhead. The default is true, making PSI displays the default mechanism of memory pressure detection for lmkd. Low-RAM devices 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 primarily based on the memory pressure. Due to the rigidity of the design, companions often personalized the driver so that it could work on their units. The LMK driver hooked into the slab shrinker API, which wasn't designed for heavy operations akin to looking for targets and killing them, which slowed down the vmscan process. The userspace lmkd implements the same performance as the in-kernel driver but makes use of present kernel mechanisms to detect and estimate memory pressure. Such mechanisms include utilizing kernel-generated vmpressure events or stress stall information (PSI) monitors to get notifications about memory pressure levels, and using memory cgroup options to restrict the memory sources allotted to every course of based on course of importance.

In Android 9 and better, userspace lmkd activates if an in-kernel LMK driver isn't detected. Userspace lmkd supports kill strategies primarily based on vmpressure occasions or PSI displays, their severity, and other hints similar to swap utilization. On low-Memory Wave Protocol gadgets, the system should tolerate increased memory stress as a traditional mode of operation. On high-performance units, memory pressure ought to be viewed as an abnormal state of affairs and fixed before it impacts general efficiency. Userspace lmkd also helps a legacy mode in which it makes kill choices using the same strategies as the in-kernel LMK driver (that's, free memory and file cache thresholds). Configure lmkd for a selected machine utilizing the following properties. Android eleven improves the lmkd by introducing a brand new killing technique. The killing technique makes use of a PSI mechanism for memory strain detection introduced in Android 10. lmkd in Android 11 accounts for memory resource use levels and Memory Wave Protocol thrashing to stop memory starvation and performance degradation. This killing strategy replaces previous strategies and can be used on both excessive-performance and low-RAM (Android Go) units. For low-RAM gadgets, include Memory Wave cgroups. The memory killing strategy in Android 11 helps the tuning knobs and defaults listed under. These options work on both excessive-performance and low-RAM gadgets.