android10/system/core/lmkd

Android Low Memory Killer Daemon

Introduction

Android Low Memory Killer Daemon (lmkd) is a process monitoring memory state of a running Android system and reacting to high memory pressure by killing the least essential process(es) to keep system performing at acceptable levels.

Background

Historically on Android systems memory monitoring and killing of non-essential processes was handled by a kernel lowmemorykiller driver. Since Linux Kernel 4.12 the lowmemorykiller driver has been removed and instead userspace lmkd daemon performs these tasks.

Android Properties

lmkd can be configured on a particular system using the following Android properties:

ro.config.low_ram: choose between low-memory vs high-performance

                         device. Default = false.

ro.lmk.use_minfree_levels: use free memory and file cache thresholds for

                         making decisions when to kill. This mode works
                         the same way kernel lowmemorykiller driver used
                         to work. Default = false

ro.lmk.low: min oom_adj score for processes eligible to be

                         killed at low vmpressure level. Default = 1001
                         (disabled)

ro.lmk.medium: min oom_adj score for processes eligible to be

                         killed at medium vmpressure level. Default = 800
                         (non-essential processes)

ro.lmk.critical: min oom_adj score for processes eligible to be

                         killed at critical vmpressure level. Default = 0
                         (all processes)

ro.lmk.critical_upgrade: enables upgrade to critical level. Default = false

ro.lmk.upgrade_pressure: max mem_pressure at which level will be upgraded

                         because system is swapping too much. Default = 100
                         (disabled)

ro.lmk.downgrade_pressure: min mem_pressure at which vmpressure event will

                         be ignored because enough free memory is still
                         available. Default = 100 (disabled)

ro.lmk.kill_heaviest_task: kill heaviest eligible task (best decision) vs.

                         any eligible task (fast decision). Default = false

ro.lmk.kill_timeout_ms: duration in ms after a kill when no additional

                         kill will be done, Default = 0 (disabled)

ro.lmk.debug: enable lmkd debug logs, Default = false