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  - `ro.lmk.pressure_after_kill_min_score`: min oom_adj_score score threshold for
92                                 cycle after kill used to allow blocking of killing
93                                 critical processes when not enough memory was freed
94                                 in a kill cycle. Default score = 0.
95  - `ro.lmk.direct_reclaim_threshold_ms`: direct reclaim duration threshold in
96                                 milliseconds to consider the system as stuck in
97                                 direct reclaim. Default = 0 (disabled)
98  - `ro.lmk.swap_compression_ratio`: swap average compression ratio to be used when
99                                 estimating how much data can be swapped. Setting it
100                                 to 0 will ignore available memory and assume that
101                                 configured swap size can be always utilized fully.
102                                 Default = 1 (no compression).
103  - `ro.lmk.lowmem_min_oom_score`: min oom_score_adj level used to select processes
104                                 to kill when memory is critically low. Setting it
105                                 to 1001 will prevent any kills for this reason. Min
106                                 acceptable value is 201 (apps up to perceptible).
107                                 Default = 701 (all cached apps excluding the last
108                                 active one).
109
110lmkd will set the following Android properties according to current system
111configurations:
112
113  - `sys.lmk.minfree_levels`:    minfree:oom_adj_score pairs, delimited by comma
114
115  - `sys.lmk.reportkills`:       whether or not it supports reporting process kills
116                                 to clients. Test app should check this property
117                                 before testing low memory kill notification.
118                                 Default will be unset.
119