OpenJDK

This site is all about the changes I made to the OpenJDK source based on Azul Systems Memory Management Module published at http://www.managedruntime.org/.

Azul MRI

The Azul MRI released two interesting components.

• Memory Management Module for Linux
• A patched version of the OpenJDK

The memory management module is a Linux kernel patch + module and user libraries allowing fast memory allocation / rellocation.

The patched version of the OpenJDK contains the GenPauseless GC. It is a GC optimized for low to virtually no pause during garbage collection.

RMS

RMS (Remapping Mark Sweep) is a GC I implemented utilizing the Azul memory management module.

License

GPL

How it works

RMS works by partitioning the heap into pages.
Each page is two mega-byte large.
It then uses the Azul MME (memory management engine) to rellocate free pages to the end of the heap, thus compacting the heap again.

Limitations

• It is a stop the world GC
• Large objects waste pages and so free memory - give it more memory
• TLABs are two mega-byte large - keep your thread count low
• It needs a lot of memory - memory is cheap
• Soft/Weak Reference are not collected - since 2011-01-02
• The Code Cache is not unloaded - yet
• Stringtable is not collected - yet
• Symboltable is not collected - yet
• the JVM has to run as root

Benchmarks

Setup

All benchmarks were performed on the same system.

• CPU: AMD Phenom(tm) II X6 2.8 GHz
• RAM: 16 GB system memory
• System: Vanilla Debian 5 (AMD64)
• Linux Kernel: vanilla 2.6.34.5 with Azul patch + mm module
• JDK: OpenJDK 1.6 b20 source drop + RMS changes

Settings

• Java Default options: -Xms6G -Xmx6G
• RMS options: -Xms6G -Xmx6G -XX:+UseAzMME -XX:+UseRMSGC
• Azul MRI options: -Xmx4G -XX:+UseGenPauselessGC -XX:GPGCThreads=10
• Tests: the mean value (time in msec) of 100 iterations is determined

Results (synthetic)

results.xls - outdated

Test #	Style	Description	Java Default	RMS 2010-10-06	RMS 2010-10-09	RMS 2010-12-15	RMS 2010-12-18	RMS 2011-01-02
Test1.java	ST	Allocate about 1GB of byte data and release	613	287	287	267	251	247
Test2.java	ST	Allocate about 1GB of object array data and release	730	306	289	262	246	242
Test3.java	ST	Allocate about 1GB of object array data and initialize the array with objects and release	2831	622	521	440	357	383
TestMt1.java	MT	ten threads each allocating about 100MB of byte data and release	585	218	205	196	191	178
TestMt2.java	MT	10 threads allocating each about 100MB of object array data and release	2386	303	231	197	186	181
TestMt3.java	MT	10 threads each allocating about 100Mb of object array data and initialize the array with objects and release	576	923	646	497	283	267
TestMt4.java	MT	10 threads each allocating about 200MB of object array data and initialize the array with objects and release	3654	3427	2580	1806	821	775
TestMt4.java (10GB heap)	MT	10 threads each allocating about 200MB of object array data and initialize the array with objects and release 10GB heap	2793	2094	1543	1174	610	587
TestMt5.java (1000 iterations)	MT	10 threads each allocating about 100Mb of object array data and initialize the array with objects and release 1000 iterations	1005	901	669	516	284	271
TestMt5.java (1000 iterations) (10GB heap)	MT	10 threads each allocating about 100Mb of object array data and initialize the array with objects and release 1000 iterations 10GB heap	298	-	456	377	234	228

Results (dacapo)

The mean time of 25 iterations (first 5 iterations are ignored) is determined.

Test #	Description	Java Default	RMS 2011-01-02
eclipse	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 eclipse	17043	17482
fop	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 fop	380	354
h2	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 h2	14863	15271
jython	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 jython	2364	2463
luindex	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 luindex	680	664
lusearch	java -Xms2G -Xmx2G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 lusearch	1053	1300
lusearch	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 lusearch	1021	1165
pmd	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 pmd	4578	4714
xalan	java -Xms6G -Xmx6G -jar dacapo-9.12-bach.jar --no-pre-iteration-gc -n 25 -t 64 xalan	1071	1086

Conclusion

Synthetic

Dacapo

Installation

It is assumed that you use a vanilla Debian 5 (AMD64) base system
(with as many CPU cores as you can get your hands on).
I used the default GCC (4.3.2 with g++) for development.
Also install libstdc++6-4.3-pic (or libstdc++6-4.1-pic) using apt-get as I am using unordered_map.

apt-get --install libstdc++6-4.3-pic libstdc++6-4.1-pic

Kernel

• Download the patched kernel image and headers.
• Install using dpkg.
• Reboot to the new kernel
• Warning: JRockit does not work with this kernel

MRI Module / Libraries

• Download and unpack MRI
• Become root
• build all the mri modules/libraries (sub directories) using

  make && make install

• install the module

  insmod /lib/modules/2.6.34.5-azul/extra/azul_mm.ko

• reserve memory (eg. 8 GB)

  azpmem/azpmem --reserve --pages 4000

OpenJDK

• Download and unpack the binary.
  • j2sdk-b20-rms.2010-10-06
  • j2sdk-b20-rms.2010-10-09
  • j2sdk-b20-rms.2010-12-18
  • j2sdk-b20-rms.2011-01-02
• Become root
• check if it works with

  j2sdk-b20-rms.2010-10-06/bin/java -Xmx1G -XX:+UseAzMME -XX:+UseRMSGC
  

Source

• b20.2010-10-07.tar.gz - the uncleaned code
• b20.2010-10-09.tar.gz - a little cleaned up code
• b20.2010-12-15.tar.gz - several optimizations (might have to de-optimize due to rare race condition)
• b20.2010-12-18.tar.gz - several optimizations (not stable, dacapo crashes VM)
• b20.2011-01-02.tar.gz - finally managed to get reference collection working (most of dacapo now working)

Thanks

I want to thank Azul Systems for releasing this great memory management module.
Furthermore, the folks at irc://irc.oftc.net/openjdk for their great help at getting me started on this project.




(c) Pressenna Sockalingasamy