README.md
1Android Low Memory Killer Daemon
2================================
3
4
5Introduction
6------------
7
8Android Low Memory Killer Daemon (lmkd) is a process monitoring memory
9state of a running Android system and reacting to high memory pressure
10by killing the least essential process(es) to keep system performing
11at acceptable levels.
12
13
14Background
15----------
16
17Historically on Android systems memory monitoring and killing of
18non-essential processes was handled by a kernel lowmemorykiller driver.
19Since Linux Kernel 4.12 the lowmemorykiller driver has been removed and
20instead userspace lmkd daemon performs these tasks.
21
22
23Android Properties
24------------------
25
26lmkd can be configured on a particular system using the following Android
27properties:
28
29 ro.config.low_ram: choose between low-memory vs high-performance
30 device. Default = false.
31
32 ro.lmk.use_minfree_levels: use free memory and file cache thresholds for
33 making decisions when to kill. This mode works
34 the same way kernel lowmemorykiller driver used
35 to work. Default = false
36
37 ro.lmk.low: min oom_adj score for processes eligible to be
38 killed at low vmpressure level. Default = 1001
39 (disabled)
40
41 ro.lmk.medium: min oom_adj score for processes eligible to be
42 killed at medium vmpressure level. Default = 800
43 (non-essential processes)
44
45 ro.lmk.critical: min oom_adj score for processes eligible to be
46 killed at critical vmpressure level. Default = 0
47 (all processes)
48
49 ro.lmk.critical_upgrade: enables upgrade to critical level. Default = false
50
51 ro.lmk.upgrade_pressure: max mem_pressure at which level will be upgraded
52 because system is swapping too much. Default = 100
53 (disabled)
54
55 ro.lmk.downgrade_pressure: min mem_pressure at which vmpressure event will
56 be ignored because enough free memory is still
57 available. Default = 100 (disabled)
58
59 ro.lmk.kill_heaviest_task: kill heaviest eligible task (best decision) vs.
60 any eligible task (fast decision). Default = false
61
62 ro.lmk.kill_timeout_ms: duration in ms after a kill when no additional
63 kill will be done. Default = 0 (disabled)
64
65 ro.lmk.debug: enable lmkd debug logs, Default = false
66
67 ro.lmk.swap_free_low_percentage: level of free swap as a percentage of the
68 total swap space used as a threshold to consider
69 the system as swap space starved. Default for
70 low-RAM devices = 10, for high-end devices = 20
71
72 ro.lmk.thrashing_limit: number of workingset refaults as a percentage of
73 the file-backed pagecache size used as a threshold
74 to consider system thrashing its pagecache.
75 Default for low-RAM devices = 30, for high-end
76 devices = 100
77
78 ro.lmk.thrashing_limit_decay: thrashing threshold decay expressed as a
79 percentage of the original threshold used to lower
80 the threshold when system does not recover even
81 after a kill. Default for low-RAM devices = 50,
82 for high-end devices = 10
83
84 ro.lmk.psi_partial_stall_ms: partial PSI stall threshold in milliseconds for
85 triggering low memory notification. Default for
86 low-RAM devices = 200, for high-end devices = 70
87
88 ro.lmk.psi_complete_stall_ms: complete PSI stall threshold in milliseconds for
89 triggering critical memory notification. Default =
90 700
91
92lmkd will set the following Android properties according to current system
93configurations:
94
95 sys.lmk.minfree_levels: minfree:oom_adj_score pairs, delimited by comma
96
97 sys.lmk.reportkills: whether or not it supports reporting process kills
98 to clients. Test app should check this property
99 before testing low memory kill notification.
100 Default will be unset.
101