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lmkd uses PIDs to track processes, however occasionally a PID of a process might be reused without lmkd detecting that. This can happen if originally registered process crashes, PID numbers wrap around and the same PID gets reused for a different process. In this situation lmkd might kill a wrong process. To prevent this issue from occurring lmkd will track processes using their pidfd. During process registration lmkd calls sys_pidfd_open and stores returned pidfd with the process record. Returned pidfd will not be reused until lmkd closes it which happens only after the process is unregistered. This way lmkd ensures that process identification is unique and can't be reused. Bug: 135608568 Test: lmkd_unit_test with and without pidfd kernel support Change-Id: Ida10ea13905c250e47f792cdd6bd2e65aeaa3709 Signed-off-by: Suren Baghdasaryan <surenb@google.com> |
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| .. | ||
| include | ||
| libpsi | ||
| tests | ||
| Android.bp | ||
| event.logtags | ||
| liblmkd_utils.c | ||
| lmkd.c | ||
| lmkd.rc | ||
| OWNERS | ||
| README.md | ||
| statslog.c | ||
| statslog.h | ||
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
ro.lmk.swap_free_low_percentage: level of free swap as a percentage of the total swap space used as a threshold to consider the system as swap space starved. Default for low-RAM devices = 10, for high-end devices = 20
ro.lmk.thrashing_limit: number of workingset refaults as a percentage of the file-backed pagecache size used as a threshold to consider system thrashing its pagecache. Default for low-RAM devices = 30, for high-end devices = 100
ro.lmk.thrashing_limit_decay: thrashing threshold decay expressed as a percentage of the original threshold used to lower the threshold when system does not recover even after a kill. Default for low-RAM devices = 50, for high-end devices = 10
ro.lmk.psi_partial_stall_ms: partial PSI stall threshold in milliseconds for triggering low memory notification. Default for low-RAM devices = 200, for high-end devices = 70
ro.lmk.psi_complete_stall_ms: complete PSI stall threshold in milliseconds for triggering critical memory notification. Default = 700