1. Memory Tuning
Android for Low-RAM
Devices
Chris Kühl & Iago López Galeiras, Endocode AG

2. What's low-RAM?
< 512MB

3. 512MB? That's so 2012!
Why do that to yourself?
You have no choice ;)
Mod-maintainer for older device
Android on embedded devices
Virtualized Android, anyone?

4. What to tune?
Apps
Dalvik VM
Activity Manager
Linux kernel

5. Apps
Be a good citizen
Apps that manage their own memory well make the whole
system run better

6. Keep Your Apps Trim
Google says,
You should implement onTrimMemory(int) to
incrementally release memory based on current
system constraints.

7. 7 Trim Levels
Running Cached
TRIM_MEMORY_RUNNING_MODERATE TRIM_MEMORY_BACKGROUND
TRIM_MEMORY_RUNNING_LOW TRIM_MEMORY_MODERATE
TRIM_MEMORY_RUNNING_CRITICAL TRIM_MEMORY_COMPLETE
...and TRIM_MEMORY_UI_HIDDEN
TRIM_MEMORY_COMPLETE ≈ onLowMemory

8. Dalvik VM
Android Java VM
DEX format
Zygote

9. Dalvik is chatty
Dalvik's logcat output can paint a pretty good picture.
12-3015:35:43.135:D/dalvikvm(15368):GC_EXPLICITfreed39K,66%free2349K/6788K,p
aused24ms+8ms,total129ms
12-3015:35:43.682:D/dalvikvm(15368):GC_CONCURRENTfreed282K,5%free10382K/10823
K,paused5ms+4ms
12-3015:35:44.043:D/dalvikvm(15368):GC_CONCURRENTfreed319K,5%free10507K/10951
K,paused3ms+3ms
12-3015:35:44.723:D/dalvikvm(15368):GC_CONCURRENTfreed364K,5%free10568K/11079
K,paused3ms+4ms
12-3015:35:44.803:D/dalvikvm(15368):GC_FOR_ALLOCfreed312K,6%free10549K/11207K
,paused31ms
12-3015:35:45.034:D/dalvikvm(15368):GC_FOR_ALLOCfreed316K,6%free10542K/11207K
,paused48ms
12-3015:35:45.074:D/dalvikvm(15368):GC_FOR_ALLOCfreed1K,6%free10631K/11207K,
paused43ms

10. Dalvik Properties
Generally set these in PRODUCT_PROPERTY_OVERRIDES.
PRODUCT_PROPERTY_OVERRIDES:=
dalvik.vm.heapstartsize=5m
dalvik.vm.heapgrowthlimit=64m
dalvik.vm.heapsize=128m
dalvik.vm.heaptargetutilization=0.80
dalvik.vm.heapminfree=512k
dalvik.vm.heapmaxfree=2m

11. Dalvik VM - JIT
Google says...
For the really low-memory devices, we recommend
the JIT be disabled entirely.
Can save up to 1.5MB per process!

12. ActivityManager
Managing activities since 2008

13. ActivityManager & Memory
management
Continually ranks apps based on their importance to the user.

14. Adjustments
staticfinalintHIDDEN_APP_MAX_ADJ=15;
staticintHIDDEN_APP_MIN_ADJ=9;
staticfinalintSERVICE_B_ADJ=8;
staticfinalintPREVIOUS_APP_ADJ=7;
staticfinalintHOME_APP_ADJ=6;
staticfinalintSERVICE_ADJ=5;
staticfinalintBACKUP_APP_ADJ=4;
staticfinalintHEAVY_WEIGHT_APP_ADJ=3;
staticfinalintPERCEPTIBLE_APP_ADJ=2;
staticfinalintVISIBLE_APP_ADJ=1;
staticfinalintFOREGROUND_APP_ADJ=0;
staticfinalintPERSISTENT_PROC_ADJ=-12;
staticfinalintSYSTEM_ADJ=-16;

15. lowmemorykiller
A kernel module to preempt the oom and provide an interface
for user-space to prioritize apps
cat/sys/module/lowmemorykiller/parameters/adj
0,1,2,4,9,15
cat/sys/module/lowmemorykiller/parameters/minfree
3031,4218,5406,7454,8642,10158

16. Configuring
lowmemorykiller
privatefinalint[]mOomAdj=newint[]{
FOREGROUND_APP_ADJ,VISIBLE_APP_ADJ,PERCEPTIBLE_APP_ADJ,
BACKUP_APP_ADJ,HIDDEN_APP_MIN_ADJ,HIDDEN_APP_MAX_ADJ
};
privatefinallong[]mOomMinFreeLow=newlong[]{
8192,12288,16384,
24576,28672,32768
};
privatefinallong[]mOomMinFreeHigh=newlong[]{
32768,40960,49152,
57344,65536,81920
};

17. dumpsys meminfo
TotalPSSbyOOMadjustment:
18642kB:System
18642kB:system(pid451)
13979kB:Persistent
9884kB:com.android.systemui(pid1791)
4095kB:com.android.phone(pid689)
18349kB:Foreground
18349kB:com.android.launcher(pid3106)
18895kB:Visible
9498kB:com.google.process.gapps(pid735)
7078kB:com.google.process.location(pid667)
2319kB:com.android.smspush(pid795)
8222kB:Perceptible
5623kB:com.android.inputmethod.latin(pid646)
2599kB:com.android.location.fused(pid676)
2810kB:AServices
2810kB:de.telekom.droidsync(pid3117)
45844kB:Background
14552kB:android.process.acore(pid3133)
5566kB:com.google.android.syncadapters.calendar(pid3270)
5475kB:com.google.android.apps.genie.geniewidget(pid3185)
4940kB:com.google.android.gsf.login(pid3254)
4362kB:com.android.browser(pid3359)
3898kB:com.android.calendar(pid3305)
3691kB:com.android.providers.calendar(pid3286)
3360kB:com.cyanogenmod.lockclock(pid3327)

18. dumpsys activity oom (1/3)
OOMlevels:
SYSTEM_ADJ:-16
PERSISTENT_PROC_ADJ:-12
FOREGROUND_APP_ADJ:0
VISIBLE_APP_ADJ:1
PERCEPTIBLE_APP_ADJ:2
HEAVY_WEIGHT_APP_ADJ:3
BACKUP_APP_ADJ:4
SERVICE_ADJ:5
HOME_APP_ADJ:6
PREVIOUS_APP_ADJ:7
SERVICE_B_ADJ:8
HIDDEN_APP_MIN_ADJ:10
HIDDEN_APP_MAX_ADJ:15

19. dumpsys activity oom (2/3)
ProcessOOMcontrol:
PERS#7:adj=sys /F trm=15451:system/1000(fixed)
oom:max=-16hidden=10client=10empty=10curRaw=-16setRaw=-16cur=-16set=-16
keeping=truehidden=falseempty=falsehasAboveClient=false
PERS#10:adj=pers/F trm=15689:com.android.phone/1001(fixed)
oom:max=-12hidden=10client=10empty=10curRaw=-12setRaw=-12cur=-12set=-12
keeping=truehidden=falseempty=falsehasAboveClient=false
PERS#3:adj=pers/F trm=151791:com.android.systemui/u0a10030(fixed)
oom:max=-12hidden=10client=10empty=10curRaw=-12setRaw=-12cur=-12set=-12
keeping=truehidden=falseempty=falsehasAboveClient=false
Proc#0:adj=fore/FAtrm=153106:com.android.launcher/u0a10022(top-activity)
oom:max=15hidden=10client=10empty=10curRaw=0setRaw=0cur=0set=0
keeping=truehidden=falseempty=falsehasAboveClient=false
Proc#9:adj=vis /F trm=15795:com.android.smspush/u0a10032(service)
com.android.smspush/.WapPushManager<=Proc{689:com.android.phone/1001}
oom:max=15hidden=10client=10empty=10curRaw=1setRaw=1cur=1set=1
keeping=truehidden=falseempty=truehasAboveClient=false

20. dumpsys activity oom (3/3)
ProcessesthatarewaitingtoGC:
ProcessProcessRecord{422a4260735:com.google.process.gapps/u0a10033}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago
ProcessProcessRecord{422f13b0451:system/1000}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago
ProcessProcessRecord{4247c388667:com.google.process.location/u0a10033}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago
ProcessProcessRecord{4231a630646:com.android.inputmethod.latin/u0a10021}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago
ProcessProcessRecord{4250cfe0676:com.android.location.fused/u0a10018}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago
ProcessProcessRecord{422f2dd81791:com.android.systemui/u0a10030}
lowMem=true,lastgced=3110616msago,lastlowMem=18198msago

21. Now for the
Kernel Bits

22. KSM
Kernel SamePage Merging
KSM can save about 20-30MB of RAM if given a chance

23. Enabling KSM
This is easy-peasy
echo1|tee/sys/kernel/mm/ksm/run
echo1000|tee/sys/kernel/mm/ksm/sleep_millisecs
echo128|tee/sys/kernel/mm/ksm/pages_to_scan

24. Oh yeah...
You need to mark pages as mergeable.
void*mmap(void*addr,size_tsize,intprot,intflags,intfd,off_toffset){
...
if(result!=MAP_FAILED&&(flags&(MAP_PRIVATE|MAP_ANONYMOUS))!=0){
ErrnoRestorererrno_restorer;
madvise(result,size,MADV_MERGEABLE);
}
returnresult;
}

25. Is it working?
dumpsys meminfo answers this
TotalPSS:126741kB
KSM:6672kBsavedfromshared1128kB
24552kBunshared;102936kBvolatile

26. extra_free_kbytes
Raises the low water mark used to trigger kswapd

27. References
Dalvik VM Internals - 2008 Google I/O
A JIT Compiler for Android's Dalvik VM - 2010 Google I/O
Running Android with low RAM
Managing Your App's Memory
Investigating your RAM Usage
Understanding the Linux Virtual Memory Manager - Zones
Reducing Memory Access Lateny

28. THE END