Use boolean allocation options #1400
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This is useful if the VM cannot trigger GC at most of its allocation sites. If allocation over-commits while still triggering GC, the GC thread can pause the mutators at the nearest safepoints.
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We remove
OnAllocationFailand add three boolean fields toAllocationOptions:allow_polling: whether this allocation attempt allows polling and trigger GCat_safepoint: whether this allocation is at a safepoint, allowing it to block for GC when GC is triggeredallow_overcommit: whether we allow overcommitThis will allow new combinations that cannot be expressed by the previous
OnAllocationFailtype. Particularly, it allows both polling and over-committing to happen in one allocation attempt. If this allocation is also not at a safepoint, this combination will allow the current mutator to allocate normally in this allocation, but block for GC at the nearest safepoint.Note: This PR implements the idea proposed in #1382 (comment). I created a new PR because the resulting commit will be radically different from #1382.
TODO:
AllocationOptionscan still be stored and loaded atomically. It should suffice if its size is smaller than the word size. If Rust is unhappy with three boolean fields, replace it with a bit field.This PR supersedes the following PRs: