Refactor both Mmapper impls into ChunkStateMmapper #1369
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We make Mmapper a struct instead of trait. It will be solely responsible for transitioning the map states. Existing implementations, including `ByteMapMmapper` and `TwoLevelMmapper`, become the storage backends of `Mmapper`. They are only responsible for maintaining the (one-level or two-level) array of `Atomic<MapState>`, and provide high-level functions for bulk-setting and bulk-transitioning map states. Methods of `MapState` are moved to `Mmapper`.
They are now only responsible for the storage, not mmapping.
We keep the Mmapper trait, and create a ChunkStateMmapper that work at chunk granularity.
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Unlike #1345, this PR retains the |
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It is no longer a constant, but a property of the `Mmapper`.
Just use BYTES_IN_CHUNK
Because `ensure_mapped` is called very often, we want it to be fast.
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The two existing
Mmapperimplementations, namelyByteMapMmapperandTwoLevelMmapperhave much duplicated code.We introduce
ChunkStateMmapperwhich implements a chunk-grainedMmapperbacked by a logical array ofMapStateelements, one for each chunk. It is responsible for actually callingmmapon memory regions. TheByteMapMmapperandTwoLevelMmapperbecomeByteMapStateStorateandTwoLevelStateStorage, respectively, and they are only responsible for holding the per-chunk states and iterating over ranges of memory to helpChunkStateMmapper. We retains the traitMmapperso that we can still implement other memory mappers that work at different granularities.MapStateis now a pure data type, and state-transitioning methods previously implemented inimpl MapStateare inlined into methods ofChunkStateMmapper.We also removed the constant
MMAP_CHUNK_BYTES. It was defined asBYTES_IN_CHUNK, but it seemed to convey the message that the "mmap chunk" is special and can have a size that is different from "chunk". We instead added a functionMmapper::granularity()which returns the actual granularity of the mmapper.