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Add README file providing lmkd overview and description for its properties. Change-Id: I30236dd4ccaa2b48c31dfb80b63f0b82b49b5744 Signed-off-by: Suren Baghdasaryan <surenb@google.com>
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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.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