412370 - GC collection heuristics busted

Status: VERIFIED DUPLICATE of bug 486504

(Tamarin Graveyard :: Garbage Collection (mmGC), defect, P2)

Description

[Tommy Reilly]

if(!marking && !collecting &&
			heapSizeAtLastAlloc > collectThreshold &&
			now - lastSweepTicks > kMarkSweepBurstTicks && 
			heapSizeAtLastAlloc < heap->GetTotalHeapSize()) 
		{
			if(incremental)
				StartIncrementalMark();
			else
				Collect();
		}

Should be:

	if((!marking && !collecting &&
			heapSizeAtLastAlloc > collectThreshold &&
			now - lastSweepTicks > kMarkSweepBurstTicks) 
                     || 
			heapSizeAtLastAlloc < heap->GetTotalHeapSize()) 
		{
			if(incremental)
				StartIncrementalMark();
			else
				Collect();
		}

Written this way the first clause will be true frequently, its missing a condition based on kFreeSpaceDivisor (collect if the free space is less than the total heap size / kFreeSpaceDivisor)

This has been working okay in practice accidentally b/c non-GC allocations are so common in the player.

Comment 1

[Dan Schaffer]

is this still active? has the fix been integrated in mmgc?

Comment 2

[Lars T Hansen]

Alive and well.

Comment 3

[Lars T Hansen]

See also bug #486504 for related issues.