`G1BlockOffsetTablePart::alloc_block(blk_start, blk_end)` updates BOT entries for the heap memory range `[blk_start, blk_end)` (already allocated by the caller). However, the method name suggests it "allocates a block at `[blk_start, blk_end)`".

I suggest to rename it to `update_for_block` to avoid misinterpretation.