MMTk 0.16.0

GC Plans

• Refactor MarkSweep to work with both our native mark sweep policy and the malloc mark sweep policy backed by malloc libraries.

Allocators

• Add FreeListAllocator which is implemented as a MiMalloc allocator.
• Fix a bug in ImmixAllocator that alignment is properly taken into consideration when deciding whether to do overflow allocation.

Policies

• Add MarkSweepSpace:
  • It uses our native MiMalloc implementation in MMTk core.
  • When the feature malloc_mark_sweep is enabled, it uses the selected malloc library to back up its allocation.
• Malloc mark sweep now accounts for memory based on page usage, and each malloc library may use a different page size.
• The immix space now uses the newly added BlockPageResource.
• Changes to Space Function Table (SFT) to improve our boot time and reduce the memory footprint:
  • Rename the current SFT map to SFTSparseChunkMap, and only use it for 32 bits architectures.
  • Add SFTSpaceMap and by default use it for 64 bits architectures.
  • Add SFTDenseChunkMap and use it when we have no control of the virtual address range for a MMTk space on 64 bits architectures.

API

• Add an option thread_affinity to set processor affinity for MMTk GC threads.
• Add AllocationSemantics::NonMoving to allocate objects that are known to be non-moving at allocation time.
• Add ReferenceGlue::is_referent_cleared to allow some bindings to use a special value rather than a normal null reference for a cleared referent.
• Add pin, unpin, and is_pinned for object pinning. Note that some spaces do not support object pinning, and using these methods may
  cause panic if the space does not support object pinning.
• Refactor ObjectReference:
  • MMTk core now pervasively uses ObjectModel::ref_to_address to get an address from an object reference for setting per-object side metadata.
  • Add ObjectModel::address_to_ref that does the opposite of ref_to_address: getting an object reference from an address that is returned by ref_to_address.
  • Add ObjectModel::ref_to_header for the binding to tell us the base header address from an object reference.
  • Rename ObjectModel::object_start_ref to ObjectModel::ref_to_object_start (to be consistent with other methods).
  • Remove ObjectModel::OBJECT_REF_OFFSET_BEYOND_CELL, as we no longer use the raw address of an object reference.
  • Add ObjectModel::UNIFIED_OBJECT_REFERENCE_ADDRESS. If a binding uses the same address for ObjectReference, ref_to_address and ref_to_object_start,
    they should set this to true. MMTk can utilize this information for optimization.
  • Add ObjectModel::OBJECT_REF_OFFSET_LOWER_BOUND to specify the minimam value of the possible offsets between an allocation result and object reference's raw address.
• destroy_mutator() no longer requires a boxed mutator as its argument. Instead, a mutable reference to the mutator is required. It is made clear that the binding should
  manage the lifetime of the boxed mutator from a bind_mutator() call.
• Remove VMBinding::LOG_MIN_ALIGNMENT and VMBinding::MAX_ALIGNMENT_SHIFT (so we only keep VMBinding::MIN_ALIGNMENT and VMBinding::MAX_ALIGNMENT).

Misc

• Add a lock-free BlockPageResource that can be used for policies that always allocate memory at the granularity of a fixed sized block.
  This page resource facilitates block allocation and reclamation, and uses lock-free operations where possible.
• Fix a race condition in FreeListPageResource when multiple threads release pages.
• Fix a bug in fetch_and/or in our metadata implementation.
• Fix a bug in side metadata bulk zeroing that may zero unrelated bits if the zeroed region cannot be mapped to whole metadata bytes.
• Remove unused meta_data_pages_per_region in page resource implementations.
• Remove the use of MaybeUninit::uninit().assume_init() in FreeListPageResource which has undefined behaviors
  and causes the illegal instruction error with newer Rust toolchains.
• Remove the trait bound From<Address> and Into<Address> for Region, as we cannot guarantee safe conversion between those two types.
• Extract Chunk and ChunkMap from the immix policy, and make it available for all the policies.