Garbage First Garbage Collection外文翻译、在线看

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ConfidentialPresentation_ID1AgendaIssues

in

GCOverview

on

G1Inside

G1

(Evacuation)Inside

G1

(Concurrent

Mark,

aka

CM)Advance

TopicsIssues

in

GCLong

PauseGC

timeApplication

TimeToo

long

to

affordFragmentationHeapPopular

Garbage

Collectors

(I)GenerationalyoungoldheapYoungor

old

are

themin

GC

unit.

The

grain

sizeIs

very

large.Popular

Garbage

Collectors

(II)CMSfragmentation

CMS

with

compactionlong

pauseOverview

on

G1What

can

we

get

from

G1

(I)1.

Control

Pause

Time

2.

Control

GC

IntervalGC

timeApplication

TimeWhat

can

we

get

from

G1

(II)The

Goals

of

G1:Max

Pause

TimePause

IntervalMemory

FragmentationG1

does

not

promise

the

first

two

Goals

will

bmet,

only

try

to

meet.When

to

adopt

G1

(I)Born

forServersWhen

to

adopt

G1

(II)Heap

is

largeCan’t

afford

long

pause

timeFragmentation

is

a

concern.How

G1

looks

like?Heap

is

divided

intofixed-size

regions,Some

as

young,Some

as

old.Heapfree

youngoldInside

G1(Evacuation)How

to

identify

live

objects

in

a

region

(Remember

SetABCDRegion

1Region

2Region

3How

to

identify

live

objects

in

a

region

(

Each

heap

region

is

associated

with

a

datastructure

named

remember

set.

A

Remember

set

contains

pointers

into

thiregion

from

other

regions.How

to

collect

(evacuate)Region

ARegion

BMove

the

live

objects

in

a

region

to

anotherregion.Remember

the

third

goal

of

G1

?Which

regions

will

be

evacuated

(I)Garbage

FirstThe

regions

with

the

largest

garbagewill

be

evacuated.Which

regions

will

be

evacuated

(II)Full

YoungAll

and

Only

youngregions

are

put

intocollection

setCollectionSetWhich

regions

will

be

evacuated

(3)Partial

YoungAll

young

regionsand

some

old

regionswith

largest

garbageare

put

intocollection

set.CollectionSetWhen

to

Full

YoungWhen

the

garbagein

old

region

is

littlegarbageold

regionsWhen

to

Partial

YoungWhen

the

live

objectsin

old

region

is

littlelive

objectsold

regionsWhen

to

evacuateYoungRegions>=

MAX_YOUNG?How

much

MAX_YOUNG

should

be

(I)MAX_YOUNG

determine:1.

Pause

Time2.

GC

intervalGC

timeApplication

TimeHow

much

MAX_YOUNG

should

be

(I)Remember

the

first

two

goals

of

G1?Have

you

already

knowhow

much

MAX_YOUNG

should

be?How

much

MAX_YOUNG

should

be

(III)Partial

YoungAs

small

as

possible,

but

not

violate1.

Pause

Time2.

GC

intervalGC

timeApplication

TimeHow

much

MAX_YOUNG

should

be

(IV)Full

YoungAs

large

as

possible,

but

not

violate1.

Pause

Time2.

GC

intervalGC

timeApplication

TimeHow

much

MAX_YOUNG

should

be

(V)Conflict

between

Pause

Time

and

GC

IntervalIf

Conflict,

meet

GC

Interval

firstl1.

Pause

Time2.

GC

intervalGC

timeApplication

TimeInside

G1(Concurrent

Mark,aka

CM)Why

CM

needed

(I)Is

Live?ABCDRegion

1Region

2Region

3Why

CM

needed

(I)Update

remember

setCount

live

objects

for

each

regionsHow

CM

looks

like

(I)initial

markconcurrent

markremarkApplication

ThreadGC

ThreadHow

CM

looks

like

(II)Initial

(stop

the

world)mark

objects

that

is

reachable

directly

from

root

setConcurrentconcurrent

mark

live

objectsFinal

(stop

the

world)follow

references

changed

in

phase

2When

to

CM

(I)

Used

memory

exceedsthe

thresholdUSEDFREEInitiatingHeapOccupancyPercent*

HeapCapacityWhen

to

CM

(II)

And

used

memoryis

larger

than

usedmemory

after

lastcollectioncurrentlastUSEDFREEUSEDFREEAdvance

TopicsCard

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tablefind

the

first

object

in

a

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