JavaOne 2013: Garbage Collection Unleashed - Demystifying the Wizardry

Ryan A. Sciampacone – Managed Run4me Architect 24 September 2013

Garbage Collec4on Unleashed Demys4fying the Wizardry

Important Disclaimers THE INFORMATION CONTAINED IN THIS PRESENTATION IS PROVIDED FOR INFORMATIONAL PURPOSES ONLY.

WHILST EFFORTS WERE MADE TO VERIFY THE COMPLETENESS AND ACCURACY OF THE INFORMATION CONTAINED IN THIS PRESENTATION, IT IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED.

ALL PERFORMANCE DATA INCLUDED IN THIS PRESENTATION HAVE BEEN GATHERED IN A CONTROLLED ENVIRONMENT. YOUR OWN TEST RESULTS MAY VARY BASED ON HARDWARE, SOFTWARE OR INFRASTRUCTURE DIFFERENCES.

ALL DATA INCLUDED IN THIS PRESENTATION ARE MEANT TO BE USED ONLY AS A GUIDE.

IN ADDITION, THE INFORMATION CONTAINED IN THIS PRESENTATION IS BASED ON IBM’S CURRENT PRODUCT PLANS AND STRATEGY, WHICH ARE SUBJECT TO CHANGE BY IBM, WITHOUT NOTICE.

IBM AND ITS AFFILIATED COMPANIES SHALL NOT BE RESPONSIBLE FOR ANY DAMAGES ARISING OUT OF THE USE OF, OR OTHERWISE RELATED TO, THIS PRESENTATION OR ANY OTHER DOCUMENTATION.

NOTHING CONTAINED IN THIS PRESENTATION IS INTENDED TO, OR SHALL HAVE THE EFFECT OF:

-‐ CREATING ANY WARRANT OR REPRESENTATION FROM IBM, ITS AFFILIATED COMPANIES OR ITS OR THEIR SUPPLIERS AND/OR LICENSORS

Your Speaker: Ryan A. Sciampacone

• Run4me Architect @ IBM (JTC) •  Interpreters • Garbage Collec4on • Plaaorm interfacing / op4miza4on • Hardware exploita4on

(E) ryan_sciampacone@ca.ibm.com (T) @rsciampacone

• Visit the IBM Booth #5112 to meet other IBM Developers

What should you take away from all this?

• Not a tuning talk • Explore some (possibly) unexpected behavior in Java

• Your plaaorm changes performance in strange ways

• Add to your “deep knowledge” toolkit • Most importantly: To be entertained

UP TO SPEED Let’s get everyone…

Compac4on

Thread Graphic: Wikimedia Commons http://en.m.wikipedia.org/wiki/File:Process_vs._thread.svg

? Allocate

Object

Thread

Compac4on

? Allocate

Object

Thread

Compac4on

? Allocate

Object

Thread

Compac4on

Allocate

Object

Thread

Genera4onal

Object

Thread

New Old

Genera4onal

Object

Thread

New Old

Allocate

Genera4onal

Object

Thread

New Old

Allocate

Genera4onal

Object

Thread

New Old

GC Thread Graphic: Wikimedia Commons http://en.m.wikipedia.org/wiki/File:Process_vs._thread.svg

Genera4onal

Object

Thread

New Old

Genera4onal

Object

Thread

New Old

Allocate

Genera4onal

Object

Thread

New Old

Allocate

Genera4onal

Object

Thread

New Old

Genera4onal

Object

Thread

New Old

Tenure

Genera4onal

Object

Thread

New Old

Global GC Thread Graphic: Wikimedia Commons http://en.m.wikipedia.org/wiki/File:Process_vs._thread.svg

Stop the World

Duke Logo: © Oracle Recycle Symbol: Creative Commons http://commons.wikimedia.org/wiki/File:Recycle.jpg

Concurrent

Java Ac4vity

GC Ac4vity

Parallel

Java Ac4vity

GC Ac4vity

ALLOCATION Quick look at the mechanics of…

Alloca4on

Padlock: Public domain http://en.wikipedia.org/wiki/File:Viking_Age_lock.png

Object

Thread A

Alloca4on

Padlock: Public domain http://en.wikipedia.org/wiki/File:Viking_Age_lock.png

Object

Thread A

Alloca4on

Padlock: Public domain http://openclipart.org/detail/22179/lock-by-nicubunu

Object

Thread A

Private Buffer

Alloca4on

Object

Thread A

Alloca4on

Object

Thread A

FINALIZATION Gekng around to eventually talking about something you inevitably have to…

The meaning of “in scope”

Simple Finalizer

Create instance of finalizable object

No references to the finalizable object at this point

Will obj be finalized?

Example

Perhaps a bit more dangerous…

THE ORDER OF THINGS Finaliza4on

What can we expect as output?

Example

So what happened?

New Old

FinalizableObject(2)

So what happened?

New Old

So what happened?

New Old

So what happened?

New Old

Tenure

So what happened?

New Old

So what happened?

New Old

So what happened?

New Old

So what happened?

New Old

So what happened?

New Old

Finalized!

ANCHOR POINTS AND GC Finaliza4on

What about anchor points?

finalize() finalize()

What about anchor points?

Example

Why only one?

New Old

Why only one?

New Old

Allocate?

Why only one?

New Old

Allocate?

Why only one?

New Old

Allocate? Allocate?

Why only one?

New Old

Allocate? Allocate?

ICEBERGS What lies beneath the surface…

Iceberg: Jesus Diaz, Gizmodo

Out of Memory (as we know and love it)

Object

Thread

New Old

Allocate

Not all memory is “heap” memory

Object

Na4ve Resource

Object

Na4ve Resource

Object

Na4ve Resource

Keep track / Use facili4es available

• Plenty of process monitoring somware out there

• Consider resource limi4ng / thronling facili4es

SHARING MEMORY Two for me and one for you…

Two threads and one field

Object

Thread field1

field2

field<N>

“Same”

Two threads and one field

Object

Thread field1

field2

field<N>

field1

field2

field<N>

“Different”

Example

The CPU Cache (High level)

CPU: Wikipedia Commons https://en.wikipedia.org/wiki/Central_processing_unit

(0x1F89DB04)

Memory

(0x1F89DB04)

Memory

(0x1F89DB04)

Memory

(0x1F89DB04)

Memory

Cache Cache CPU

(0x1F89DB04)

Memory

Cache Cache CPU

(0x1F89DB04)

Memory

Cache Cache CPU

Two threads and two fields

Object

Thread field1

field2

field<N>

“Same”

Two threads and two fields

Object

Thread field1

field2

field<N>

field1

field2

field<N>

“Different”

Example

The CPU Cache Pt. 2 (High level)

Memory

Cache Line

Memory

Cache Line

Memory

Cache Cache CPU

Cache Line

Memory

Cache Cache CPU

Cache Line

Memory

Cache Cache CPU

Cache Line

FIELD ORDERING When ordering pizza you expect the crust on the bonom…

Subclass with fields “far apart”

Two threads and two fields and one subclass

Object

Thread

field1

field2

pad001

pad0NN

pad100 “Second”

pad1NN

field3

Two threads and two fields and one subclass

Object

Thread

field1

field2

pad001

pad0NN

pad100

pad1NN

… “Third”

field3

Example

So what happened?

field1

field2

pad001

pad0NN

pad100

pad1NN

field3

So what happened?

field1

field2

pad001

pad0NN

pad100

pad1NN

field3

So what happened?

field1 field2

pad001

pad0NN

pad100

pad1NN

field3

So what happened?

field1 field2

pad001

pad0NN

pad100

pad1NN

field3

So what happened?

field1 field2

pad001

pad0NN

pad100

pad1NN

field3

Cache Line

So what happened? (Alternate version)

field1

pad001

pad0NN

pad100

pad1NN

field2 field3

CACHE CAPACITY Spreading things out doesn’t always reduce collisions…

Small data, Big problems

byte[]

Cache Line (64 Bytes)

byte[]

4KB 4KB

byte[]

4KB 4KB

byte[]

4KB 4KB

byte[]

4KB 4KB

byte[]

4KB 4KB

byte[]

•  Access the same index from each line •  Move to the next index •  Repeat

4KB 4KB

byte[]

Example

Cache “capacity” is less than you think

Cache 8 Entries

HOW MEMORY WORKS Before I forget, a few more things about…

Non Uniform Memory Architecture (NUMA)

CPU: Wikipedia Commons https://en.wikipedia.org/wiki/Central_processing_unit DRAM: Wikipedia Commons http://en.wikipedia.org/wiki/Dynamic_random-access_memory

Non Uniform Memory Architecture

• JVMs do have support • Balanced GC policy •  -‐Xnuma

• Plaaorm commands for thronling / afini4zing •  Taskset • Numactl

• Virtualiza4on

Resource on Memory

PARTING REMARKS And finally…

Copyright and Trademarks

© IBM Corpora4on 2013. All Rights Reserved. IBM, the IBM logo, and ibm.com are trademarks or registered trademarks of Interna4onal Business Machines Corp., and registered in many jurisdic4ons worldwide.

Other product and service names might be trademarks of IBM or other companies. A current list of IBM trademarks is available on the Web – see the IBM “Copyright and trademark informa4on” page at URL: www.ibm.com/legal/copytrade.shtml

JavaOne 2013: Garbage Collection Unleashed - Demystifying the Wizardry

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Transcript of JavaOne 2013: Garbage Collection Unleashed - Demystifying the Wizardry

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