An evacuation failure while copying the roots caused an object, A, to be forwarded to itself. During the subsequent RSet updating a reference to A was processed causing the reference to be added to the RSet of A's heap region. As a result of adding to the remembered set we ran into the issue described in 6930581 - the sparse table expanded and the RSet scanning code walked the cards in one instance of RHashTable (_cur) while the occupied() counts the cards in the expanded table (_next).
Reviewed-by: tonyp, iveresov
During RSet updating, when ParallelGCThreads is zero, references that point into the collection set are added directly the referenced region's RSet. This can cause the sparse table in the RSet to expand. RSet scanning and the "occupied" routine will then operate on different instances of the sparse table causing the assert to trip. This may also cause some cards added post expansion to be missed during RSet scanning. When ParallelGCThreads is non-zero such references are recorded on the "references to be scanned" queue and the card containing the reference is recorded in a dirty card queue for use in the event of an evacuation failure. Employ the parallel code in the serial case to avoid expanding the RSets of regions in the collection set.
Reviewed-by: iveresov, ysr, tonyp
The per-worker _new_refs array is used to hold references that point into the collection set. It is populated during RSet updating and subsequently processed. In the event of an evacuation failure it processed again to recreate the RSets of regions in the collection set. Remove the per-worker _new_refs array by processing the references directly. Use a DirtyCardQueue to hold the cards containing the references so that the RSets of regions in the collection set can be recreated when handling an evacuation failure.
Reviewed-by: iveresov, jmasa, tonyp
The first worker thread is delayed when entering the GC because it clears the card count table that is used in identifying hot cards. Replace the card count table with a dynamically sized evicting hash table that includes an epoch based counter.
Reviewed-by: iveresov, tonyp
6720334: G1: don't update RSets of collection set regions during an evacuation pause
Introduced a deferred update mechanism for delaying the rset updates during the collection pause
Reviewed-by: apetrusenko, tonyp
