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[GR-51205] Avoid needlessly rescanning black objects. #8126

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Merged
merged 1 commit into from
Jan 10, 2024
Merged

[GR-51205] Avoid needlessly rescanning black objects. #8126

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4 changes: 2 additions & 2 deletions ...com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/AlignedHeapChunk.java
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Original file line number Diff line number Diff line change
Expand Up @@ -149,8 +149,8 @@ static boolean walkObjects(AlignedHeader that, ObjectVisitor visitor) {

@AlwaysInline("GC performance")
@Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
static boolean walkObjectsInline(AlignedHeader that, ObjectVisitor visitor) {
return HeapChunk.walkObjectsFromInline(that, getObjectsStart(that), visitor);
static boolean walkObjectsFromInline(AlignedHeader that, Pointer start, ObjectVisitor visitor) {
return HeapChunk.walkObjectsFromInline(that, start, visitor);
}

@Fold
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6 changes: 5 additions & 1 deletion ...om.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/GreyObjectsWalker.java
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Expand Up @@ -87,23 +87,27 @@ void walkGreyObjects() {
@Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
private void walkAlignedGreyObjects() {
AlignedHeapChunk.AlignedHeader aChunk;
Pointer aStart;
if (alignedHeapChunk.isNull() && alignedTop.isNull()) {
/* If the snapshot is empty, then I have to walk from the beginning of the Space. */
aChunk = space.getFirstAlignedHeapChunk();
aStart = (aChunk.isNonNull() ? AlignedHeapChunk.getObjectsStart(aChunk) : WordFactory.nullPointer());
} else {
/* Otherwise walk Objects that arrived after the snapshot. */
aChunk = alignedHeapChunk;
aStart = alignedTop;
}
/* Visit Objects in the AlignedChunks. */
GreyToBlackObjectVisitor visitor = GCImpl.getGCImpl().getGreyToBlackObjectVisitor();
if (aChunk.isNonNull()) {
AlignedHeapChunk.AlignedHeader lastChunk;
do {
lastChunk = aChunk;
if (!AlignedHeapChunk.walkObjectsInline(aChunk, visitor)) {
if (!AlignedHeapChunk.walkObjectsFromInline(aChunk, aStart, visitor)) {
throw VMError.shouldNotReachHereAtRuntime();
}
aChunk = HeapChunk.getNext(aChunk);
aStart = (aChunk.isNonNull() ? AlignedHeapChunk.getObjectsStart(aChunk) : WordFactory.nullPointer());
} while (aChunk.isNonNull());

/* Move the scan point. */
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14 changes: 7 additions & 7 deletions ...vm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapChunk.java
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Expand Up @@ -297,20 +297,20 @@ private static SignedWord offsetFromPointer(Header<?> that, PointerBase pointer)
}

@NeverInline("Not performance critical")
public static boolean walkObjectsFrom(Header<?> that, Pointer offset, ObjectVisitor visitor) {
return walkObjectsFromInline(that, offset, visitor);
public static boolean walkObjectsFrom(Header<?> that, Pointer start, ObjectVisitor visitor) {
return walkObjectsFromInline(that, start, visitor);
}

@AlwaysInline("GC performance")
@Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
public static boolean walkObjectsFromInline(Header<?> that, Pointer startOffset, ObjectVisitor visitor) {
Pointer offset = startOffset;
while (offset.belowThan(getTopPointer(that))) { // crucial: top can move, so always re-read
Object obj = offset.toObject();
public static boolean walkObjectsFromInline(Header<?> that, Pointer start, ObjectVisitor visitor) {
Pointer p = start;
while (p.belowThan(getTopPointer(that))) { // crucial: top can move, so always re-read
Object obj = p.toObject();
if (!callVisitor(visitor, obj)) {
return false;
}
offset = offset.add(LayoutEncoding.getSizeFromObjectInlineInGC(obj));
p = p.add(LayoutEncoding.getSizeFromObjectInlineInGC(obj));
}
return true;
}
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