[Vm-dev] VM Maker: VMMaker.oscog-eem.1670.mcz

commits at source.squeak.org commits at source.squeak.org
Mon Jan 25 05:40:58 UTC 2016 

Eliot Miranda uploaded a new version of VMMaker to project VM Maker:
http://source.squeak.org/VMMaker/VMMaker.oscog-eem.1670.mcz

==================== Summary ====================

Name: VMMaker.oscog-eem.1670
Author: eem
Time: 25 January 2016, 9:39:09.293071 pm
UUID: 6ba2dd3d-ab44-468e-9184-1c85580f980b
Ancestors: VMMaker.oscog-eem.1669

Spur: Maintain the survivor count on scavenge (seems cost free).  Nuke the special mark count variable; it's always zero anyway.

=============== Diff against VMMaker.oscog-eem.1669 ===============

Item was changed:
  CogClass subclass: #SpurGenerationScavenger
+ 	instanceVariableNames: 'coInterpreter manager eden futureSpace pastSpace futureSurvivorStart rememberedSet rememberedSetSize previousRememberedSetSize rememberedSetRedZone rememberedSetLimit refCountToShrinkRT weakList ephemeronList tenureCriterion tenureThreshold tenuringClassIndex tenuringProportion numRememberedEphemerons statSurvivorCount statTenures'
- 	instanceVariableNames: 'coInterpreter manager eden futureSpace pastSpace futureSurvivorStart rememberedSet rememberedSetSize previousRememberedSetSize rememberedSetRedZone rememberedSetLimit refCountToShrinkRT weakList ephemeronList tenureCriterion tenureThreshold tenuringClassIndex tenuringProportion numRememberedEphemerons statTenures'
  	classVariableNames: ''
  	poolDictionaries: 'SpurMemoryManagementConstants'
  	category: 'VMMaker-SpurMemoryManager'!
  
  !SpurGenerationScavenger commentStamp: 'eem 9/30/2013 11:05' prior: 0!
  SpurGenerationScavenger is an implementation of David Ungar's Generation Scavenging garbage collection algorithm.  See
  	Generation Scavenging, A Non-disruptive, High-Performance Storage Reclamation Algorithm
  	David Ungar
  	Proceeding
  	SDE 1 Proceedings of the first ACM SIGSOFT/SIGPLAN software engineering symposium on Practical software development environments
  	Pages 157 - 167 
  	ACM New York, NY, USA ©1984 
  
  Also relevant are
  	An adaptive tenuring policy for generation scavengers
  	David Ungar & Frank Jackson
  	ACM Transactions on Programming Languages and Systems (TOPLAS) TOPLAS Homepage archive
  	Volume 14 Issue 1, Jan. 1992 
  	Pages 1 - 27 
  	ACM New York, NY, USA ©1992
  and
  	Ephemerons: a new finalization mechanism
  	Barry Hayes
  	Proceedings of the 12th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications
  	Pages 176-183 
  	ACM New York, NY, USA ©1997
  
  See text below the variable definitions and explanation below for a full explanation of weak and ephemeron processing.
  
  Instance Variables
  	coInterpreter:					<StackInterpreterSimulator|CogVMSimulator>
  	eden:							<SpurNewSpaceSpace>
  	ephemeronList:					<Integer|nil>
  	futureSpace:					<SpurNewSpaceSpace>
  	futureSurvivorStart:				<Integer address>
  	manager:						<SpurMemoryManager|Spur32BitMMLESimulator et al>
  	numRememberedEphemerons:	<Integer>
  	pastSpace:						<SpurNewSpaceSpace>
  	previousRememberedSetSize:	<Integer>
  	rememberedSet:				<CArrayAccessor on: Array>
  	rememberedSetSize:			<Integer>
  	tenuringProportion:				<Float>
  	tenuringThreshold:				<Integer address>
  	weakList:						<Integer|nil>
  
  coInterpreter
  	- the interpreter/vm, in this context, the mutator
  
  manager
  	- the Spur memory manager
  
  eden
  	- the space containing newly created objects
  
  futureSpace
  	- the space to which surviving objects are copied during a scavenge
  
  futureSurvivorStart
  	- the allocation pointer into futureSpace
  
  pastSpace
  	- the space surviving objects live in until the next scavenge
  
  rememberedSet
  	- the root old space objects that refer to objects in new space; a scavenge starts form these roots and the interpreter's stack
  
  rememberedSetSize
  	- the size of the remembered set, also the first unused index in the rememberedSet
  
  previousRememberedSetSize:
  	- the size of the remembered set before scavenging objects in future space.
  
  numRememberedEphemerons
  	- the number of unscavenged ephemerons at the front of the rememberedSet.
  
  ephemeronList
  	- the head of the list of corpses of unscavenged ephemerons reached in the current phase
  
  weakList
  	- the head of the list of corpses of weak arrays reached during the scavenge.
  
  tenuringProportion
  	- the amount of pastSpace below which the system will not tenure unless futureSpace fills up, and above which it will eagerly tenure
  
  tenuringThreshold
  	- the pointer into pastSpace below which objects will be tenured
  
  Weakness and Ephemerality in the Scavenger.
  Weak arrays should not hold onto their referents (except from their strong fileds, their named inst vars).  Ephemerons are objects that implement instance-based finalization; attaching an ephemeron to an object keeps that object alive and causes the ephemeron to "fire" when the object is only reachable from the ephemeron (or other ephemerons & weak arrays).  They are a special kind of Associations that detect when their keys are about to die, i.e. when an ephemeron's key is not reachable from the roots except from weak arrays and other ephemerons with about-to-die keys.  Note that if an ephemeron's key is not about to die then references from the rest of the ephemeron can indeed prevent ephemeron keys from dying.
  
  The scavenger is concerned with collecting objects in new space, therefore it ony deals with weak arrays and ephemerons that are either in the remembered set or in new space.  By deferring scanning these objects until other reachable objects have been scavenged, the scavenger can detect dead or dying references.
  
  Weak Array Processing
  In the case of weak arrays this is simple.  The scavenger refuses to scavenge the referents of weak arrays in scavengeReferentsOf: until the entire scavenge is over.  It then scans the weak arrays in the remembered set and in future space and nils all fields in them that are referring to unforwarded objects in eden and past space, because these objects have not survived the scavenge.  The root weak arrays remaining to be scavenged are in the remembered table.  Surviving weak arrays in future space are collected on a list.  The list is threaded through the corpses of weak arrays in eden and/or past space.  weakList holds the slot offset of the first weak array found in eden and/or past space.  The next offset is stored in the weak array corpse's identityHash and format fields (22 bits & 5 bits of allocationUnits, for a max new space size of 2^28 bytes, 256Mb).  The list is threaded throguh corpses, but the surviving arrays are pointed to by the corpses' forwarding pointers.
  
  Ephemeron Processing
  The case of ephemerons is a little more complicated because an ephemeron's key should survive.  The scavenger is cyclical.  It scavenges the remembered set, which may copy and forward surviving objects in past and/or eden spaces to future space.  It then scavenges those promoted objects in future space until no more are promoted, which may in turn remember more objects.  The cycles continue until no more objects get promoted to future space and no more objects get remembered.  At this point all surviving objecta are in futureSpace.
  
  So if the scavenger does not scan ephemerons in the remembered set or in future space until the scavenger finishes cycling, it can detect ephemerons whose keys are about to die because these will be unforwarded objects in eden and/or past space.  Ephemerons encountered in the remembered set are either processed like ordinary objects if their keys have been promoted to futureSpace, or are moved to the front of the rememberedSet (because, dear reader, it is a sequence) if their keys have not been promoted.  Ephemerons encountered in scavengeReferentsOf: are either scanned like normal objects if their keys have been promoted, or added to the ephemeronList, organized identically to the weakList, if their keys are yet to be promoted.  Since references from other ephemerons with surviving keys to ephemeron keys can and should prevent the ephemerons whose keys they are from firing the scavenger does not fire ephemerons unless all unscavenged ephemerons have unscavenged keys.  So the unscavenged ephemerons (the will be at the beginning of the remembered set and on the ephemeronList) are scanned and any that have promoted keys are scavenged.  But if no unscavenged ephemerons have surviving keys then all the unscavenged ephemerons are fired and then scavenged.  This in turn may remember more objects and promote more objects to future space, and encounter more unscavenged ephemerons.  So the scavenger continues until no more objects are remembered, no more objects are promoted to future space and no more unscavenged ephemerons exist.!

Item was changed:
  ----- Method: SpurGenerationScavenger>>copyToFutureSpace:bytes: (in category 'scavenger') -----
  copyToFutureSpace: survivor bytes: bytesInObject
  	"Copy survivor to futureSpace.  Assume it will fit (checked by sender).
  	 Answer the new oop of the object (it may have an overflow size field)."
  	<inline: true>
  	| startOfSurvivor newStart |
+ 	statSurvivorCount := statSurvivorCount + 1. "we hope writes are cheap..."
  	self assert: futureSurvivorStart + bytesInObject <= futureSpace limit.
  	startOfSurvivor := manager startOfObject: survivor.
  	newStart := futureSurvivorStart.
  	futureSurvivorStart := futureSurvivorStart + bytesInObject.
  	manager mem: newStart asVoidPointer cp: startOfSurvivor asVoidPointer y: bytesInObject.
  	tenureCriterion = TenureToShrinkRT ifTrue:
  		[manager rtRefCountOf: newStart + (survivor - startOfSurvivor) put: 0].
  	^newStart + (survivor - startOfSurvivor)!

Item was changed:
  ----- Method: SpurGenerationScavenger>>initialize (in category 'initialization') -----
  initialize
  	pastSpace := SpurNewSpaceSpace new.
  	futureSpace := SpurNewSpaceSpace new.
  	eden := SpurNewSpaceSpace new.
  	rememberedSetSize := 0.
  	tenureThreshold := 0.
+ 	statSurvivorCount := statTenures := 0!
- 	statTenures := 0!

Item was changed:
  ----- Method: SpurGenerationScavenger>>scavenge: (in category 'scavenger') -----
  scavenge: tenuringCriterion
  	"The main routine, scavenge, scavenges young objects reachable from the roots (the stack zone
  	 and the rememberedTable).  It first scavenges the new objects immediately reachable from old
  	 ones (all in the remembered table), then the stack zone.  Then it scavenges those that are
  	 transitively reachable.  If this results in a promotion, the promotee gets remembered, and it first
  	 scavenges objects adjacent to the promotee, then scavenges the ones reachable from the
  	 promoted.  This loop continues until no more reachable objects are left.  At that point,
  	 pastSurvivorSpace is exchanged with futureSurvivorSpace.  Then any surviving weakArrays and
  	 weakArrays in the remembered set can be processed and their dead elements nilled.
  
  	 By default promotion (tenuring) is based on age and ammount of objects scavenged.  But
  	 tenuring can be based on e.g. a particular class.  The argument selects the tenuring criterion.
  
  	 Answer the limit of pastSpace, to allow the memory manager to bounds check survivors."
+ 	statSurvivorCount := 0.
  	tenureCriterion := tenuringCriterion.
  	self strategizeToLimitRememberedTable.
  	self scavengeLoop.
  	self processWeaklings.
  	self computeTenuringThreshold.
  	self exchangeSurvivorSpaces.
  	^self initFutureSpaceStart!

Item was added:
+ ----- Method: SpurGenerationScavenger>>statSurvivorCount (in category 'accessing') -----
+ statSurvivorCount
+ 	^statSurvivorCount!

Item was changed:
  CogClass subclass: #SpurMemoryManager
(excessive size, no diff calculated)

Item was changed:
  ----- Method: SpurMemoryManager>>initialize (in category 'initialization') -----
  initialize
  	"We can put all initializations that set something to 0 or to false here.
  	 In C all global variables are initialized to 0, and 0 is false."
  	remapBuffer := Array new: RemapBufferSize.
  	remapBufferCount := extraRootCount := 0. "see below"
  	freeListsMask := totalFreeOldSpace := lowSpaceThreshold := 0.
  	checkForLeaks := 0.
  	needGCFlag := signalLowSpace := scavengeInProgress := marking := false.
  	becomeEffectsFlags := 0.
  	statScavenges := statIncrGCs := statFullGCs := 0.
  	statScavengeGCUsecs := statIncrGCUsecs := statFullGCUsecs := statGCEndUsecs := 0.
  	statSGCDeltaUsecs := statIGCDeltaUsecs := statFGCDeltaUsecs := 0.
+ 	statGrowMemory := statShrinkMemory := statRootTableCount := 0.
+ 	statRootTableOverflows := statMarkCount := statCompactPassCount := statCoalesces := 0.
- 	statGrowMemory := statShrinkMemory := statRootTableCount := statSurvivorCount := 0.
- 	statRootTableOverflows := statMarkCount := statSpecialMarkCount := statCompactPassCount := statCoalesces := 0.
  
  	"We can initialize things that are allocated but are lazily initialized."
  	unscannedEphemerons := SpurContiguousObjStack new.
  
  	"we can initialize things that are virtual in C."
  	scavenger := SpurGenerationScavengerSimulator new manager: self; yourself.
  	segmentManager := SpurSegmentManager new manager: self; yourself.
  
  	"We can also initialize here anything that is only for simulation."
  	heapMap := CogCheck32BitHeapMap new.
  
  	"N.B. We *don't* initialize extraRoots because we don't simulate it."
  
  	maxOldSpaceSize := self class initializationOptions ifNotNil: [:initOpts| initOpts at: #maxOldSpaceSize ifAbsent: [0]]!

Item was changed:
  ----- Method: SpurMemoryManager>>statSpecialMarkCount (in category 'accessing') -----
  statSpecialMarkCount
+ 	^0!
- 	^statSpecialMarkCount!

Item was changed:
  ----- Method: SpurMemoryManager>>statSurvivorCount (in category 'accessing') -----
  statSurvivorCount
+ 	<doNotGenerate>
+ 	^scavenger statSurvivorCount!
- 	^statSurvivorCount!

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