Progress report - JVM GC + OS Swap - Journaling in Lustre

1. Hyojeong Lee
Distributed Computing System Laboratory
Department of Computer Science and Engineering
Seoul National University, Korea
Progress Report

2. Table of Contents
DOING TODO
Swap-aware
JVM GC
1차 구현 내용 정리
- 모듈별 실행시간
- Evaluation 보완 (SPECjvm)
Page level 재구현
- 관련 연구 참고
Page level 완료
- Validation (DL4J, Spark)
- Compare with other policies
Plan for optimized GC
Journaling in
Lustre FS
서베이 및 논문 수정 최적화 및 실험 추가

3. Swap-aware JVM GC: 1차 정리
● Motivation:
● Necessity of OS swap
● JVM GC policy is not aware of OS swap
● Background: GC process

4. Swap-aware JVM GC: 1차 정리
● Scheme: Skip source-destination mapping
● Validation: with test program

5. ● SPECjvm2008 for evaluation (heap)
● scimark.fft.large (4G), crypto.aes (1G), serial (2G),
xml.validation (0.5G)
● derby (2G)
Swap-aware JVM GC: 1차 정리
Swapout Swapin

6. ● Problem
● Current GC doesn’t allow free space between live objects.
● In detail, verifying object before/after GC will fail if object is
free(hole).
● Solution
● Goal
● Avoid source-destination mapping of regions to skip,
without modifying existing metadata and policy.
● Ours
● Set metadata (i.e. dest_addr) properly considering swapness.
● Problem (debugging)
● full_cp and dense prefix are changed.
(cf) first_dead_space_region()
● Related work (APSys’18, VEE’19)
● Insert dummy objects.
Swap-aware JVM GC: 재구현

7. ● Solution (in detail)
● Related work
● summarize_skip_ver()
: insert dummy objects to hole.
Swap-aware JVM GC: 재구현

8. ● 내용 파악/수정
Serialization due to waiting
transaction commit
→ Parallel journal commit
● 최적화 및 실험 추가 (Todo)
i.e. mdtest
Journaling in Lustre FS

9. TODO
DONE/DOING TODO
Swap-aware
JVM GC
1차 구현 내용 정리 ~3/18
- 모듈별 실행시간
- Evaluation 보완 (SPECjvm)
Page level 재구현 ~3/18
- 관련 연구 참고
Page level 완료 ~3/29
- Validation (DL4J, Spark)
- Compare with other policies
Plan for optimized GC Next
Journaling in
Lustre FS
서베이 및 논문 수정 ~3/15(Done) 최적화 및 실험 추가 Next

10. Bkup_Target workloads (~ 3/15)

11. ● Attempts
1. Can’t skip entire memcpy.
2. ‘Validation after GC error’ because of wrong metadata.
3. DOING
● Evaluation
● Simple java program (microbench)
● Make swapped objects target for compaction
● Benchmarks (benchmark)
● DaCapo, SPECjvm2008, JOlden, Hyracks
● Neo4j (real workload)
● embedded, disk-based, fully transactional Java persistence engine that
manages graph data
● Spark (real workload)
● Sparkbench’s Graph-computation & Machine-learning algorithm
● Deeplearning4Java (real workload)
● Deep learning platform for Java
Target list

12. ● SPECjvm2008 for evaluation
● scimark.fft.large (4G)
● derby (2G)
● crypto.aes (1G)
● serial (2G)
● xml.validation (0.5G)
SPECjvm2008

13. ● Kernel(page) level: Swap flag - Attempt (2)
● Evaluation w/ DL4J
● Object Detection: House Number Detection
● Dataset: http://ufldl.stanford.edu/housenumbers/
● 73,257 digit images for training
● 26,032 digit images for testing
● 531,131 additional, somewhat less difficult samples, to use as
extra training data
● Result
● Baseline (DONE)
● Iteration for training: 100 times
● FGC: 2 times
● Memory usage: ~ 9 GB
● Optimized (TODO)
DL4J

14. ● Kernel(page) level: Swap flag - Attempt (2)
● Evaluation w/ Spark
● Proper target
● SVDPlusPlus
● LogisticRegression
● How to execute?
● 환경 구축, https://docs.google.com/document/d/1seI-
ZzjKvcJeMOJFLLWX0hys7bJVla5TsTobtgrguAE/edit?usp=sh
aring
● 실험 방법,
https://docs.google.com/document/d/1eL5sGQrzUMM3SffME
yp0gQ1qeh7oJ3dbOD2TW6LPy9M/edit?usp=sharing
● Sparkbench 분석 및 베이스라인 실험 결과,
https://docs.google.com/presentation/d/1VYHK2550iJjVg4BeL
zavviCvdDQrehRZ_1oXN27CDKg/edit?usp=sharing
Spark (sparkbench)

15. (cf) Other JVM GC policies
# Policy
Copy swapped
obj
Traverse for
allocation
Other issues etc
1
Concurrent Mark
and Sweep (CMS)
X O
Floating garbage /
More logics to deal with fragmentation /
More space for list
long-lived obj 비율 높고 pause
time 제약 있는 앱에 적합
2 Parallel Compact O X X
pause time 제약 있는 앱에 적합
default in java 8
3 Garbage first (G1) O X X default in java 9
4
SAGP (Swap-
aware Parallel
Compact)
X X
Floating garbage /
Check pagemap (fopen, close) /
More fragmentation
기존 allocation 정책 그대로 사용
가능
커널의 swap 정보를 역으로 읽어
올 수 있으면 오버헤드 제거 가능
https://docs.google.com/presentation/d/1rLyJyny7NMmSLpd9f_z_arjzzngL4bxjAbgo0d5Lnik/edit?usp=sharing

16. Backup slides

17. ● Solutions
● Swap-aware GC policy
● (Fine-grained) Checking pagemap → Inserting DS maintaining
swap info
● (Coarse-grained) Adding reference counter + LRU list
● Optimized GC policy (TODO)
Solutions
dense_prefix
Virtual (heap)
Physical (kernel)
Actually, no need to compact
→ Just remapping virtual space!

18. ● Implementation scheme
Swap-aware JVM GC Policy
dense_prefix
Swap space Swapped live data
Process of Full GC
1. Mark
2. Summarize
3. Compact
Assume that,
- Swapped region =
LRU → Do not need to
swapin.
source_reg
dest_addr
live_size
…
512k
Metadata of Region
Bitmap
1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 1
Add variable
‘_swpness’ &
check it using
pagemap
1. Mark
: Set bit for live object by
tracking root set
2. Summarize
: Fill metadata & set
dense prefix
3. Compact
: push_region to stack → do sliding
compaction (memcpy)
…
Region stack list
Region stacks for each GC thread
When src’s _swpness > 0,
skip pushing/copying
draining and
stealing over
stacks

19. ● Kernel(page) level: Swap flag - Attempt (1)
● Evaluation w/ Simple java program
● Simple java program
● Make swapped objects target for compaction
● Result
Swap-aware JVM GC Policy
Allocate 30
objects
Allocate 10 objects
(objects 0 to 9 are
swapped out)
Access 0 to 9 (objects 10 to
19 are swapped out)
&
Make null objects 0 to 9 (be
GC targets)
GC triggered, do mark and
summarize (checking swpness
consumes about 24 sec)
Do compact
Allocate 30
objects
Allocate 10 objects
(objects 0 to 9 are
swapped out)
Access 0 to 9 (objects 10 to
19 are swapped out)
&
Make null objects 0 to 9 (be
GC targets)
GC triggered, do mark and
summarize & Do compact

20. ● Kernel(page) level: Swap flag - Attempt (2)
● Evaluation w/ Simple java program
Swap-aware JVM GC Policy

21. ● Kernel(page) level: Swap flag - Attempt (2)
● Evaluation w/ Simple java program
Swap-aware JVM GC Policy