Starting March 27, 2025, we suggest using android-newest-launch as an alternative of aosp-important 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 primarily based in your preferences. The Android low Memory Wave killer daemon (lmkd) course of displays the memory state of a operating Android system and reacts to high memory stress by killing the least essential processes to maintain the system performing at acceptable ranges. An Android system operating a number of processes in parallel could encounter situations when system memory is exhausted and processes that require more memory expertise noticeable delays. Memory pressure, Memory Wave memory booster a state through which the system is operating 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. Traditionally, Android monitored system memory stress using an in-kernel low memory killer (LMK) driver, a rigid mechanism that is determined by exhausting-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 higher support a brand new lmkd mode that makes use of kernel strain stall data (PSI) displays for memory stress detection. The PSI patchset in the upstream kernel (backported to 4.9 and 4.14 kernels) measures the period of time that duties are delayed on account of memory shortages. As these delays immediately have an effect on user expertise, they signify a handy metric for figuring out memory stress severity. The upstream kernel also includes PSI screens that permit privileged userspace processes (comparable 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 pressure detection and used by lmkd) often include quite a few false positives, lmkd should perform filtering to find out if the memory is under actual stress.
This leads to pointless lmkd wakeups and the use of extra computational assets. Using PSI monitors outcomes in additional accurate memory strain detection and minimizes filtering overhead. The default is true, making PSI monitors the default mechanism of memory pressure detection for lmkd. Low-RAM devices needed to be tuned aggressively, and even then would perform poorly on workloads with large file-backed lively pagecache. The poor performance resulted in thrashing and no kills. The LMK kernel driver relied on free-memory limits, with no scaling based on the memory strain. Due to the rigidity of the design, partners typically personalized the driver in order that it might work on their units. The LMK driver hooked into the slab shrinker API, which wasn't designed for heavy operations equivalent to trying to find targets and killing them, which slowed down the vmscan process. The userspace lmkd implements the identical functionality because the in-kernel driver but uses current kernel mechanisms to detect and estimate memory pressure. Such mechanisms embrace utilizing kernel-generated vmpressure events or strain stall data (PSI) monitors to get notifications about memory stress levels, and using memory cgroup features to restrict the memory assets allotted to every process based on process importance.
In Android 9 and higher, userspace lmkd activates if an in-kernel LMK driver is not detected. Userspace lmkd supports kill methods primarily based on vmpressure occasions or PSI screens, their severity, and different hints corresponding to swap utilization. On low-memory units, the system ought to tolerate increased Memory Wave memory booster stress as a traditional mode of operation. On high-performance gadgets, memory pressure should be seen as an abnormal scenario and fixed earlier than it impacts overall efficiency. Userspace lmkd additionally supports a legacy mode during which it makes kill selections using the same strategies because the in-kernel LMK driver (that's, free memory and file cache thresholds). Configure lmkd for a selected machine utilizing the next properties. Android eleven improves the lmkd by introducing a new killing strategy. The killing technique makes use of a PSI mechanism for memory strain detection introduced in Android 10. lmkd in Android eleven accounts for memory resource use levels and thrashing to stop memory starvation and performance degradation. This killing strategy replaces previous methods and can be utilized on each high-efficiency and low-RAM (Android Go) gadgets. For low-RAM gadgets, include memory cgroups. The memory killing technique in Android eleven supports the tuning knobs and Memory Wave defaults listed below. These features work on each high-efficiency and low-RAM gadgets.