ADR-0005: Virtual Memory Model

Status

Accepted

Context

The OS must support strong isolation, future compatibility runtimes, memory-mapped files, and multicore-safe execution.

Decision

The virtual memory model uses:

• per-process address spaces
• higher-half kernel mapping
• direct physical map for kernel internal operations
• explicit memory objects backing mappings
• copy-on-write support
• file-backed and shared-memory mappings

Consequences

Positive:

• clear ownership and accounting for mappings
• strong base for compatibility runtimes
• natural integration with page cache and filesystem services

Negative:

• VM subsystem design is more complex than a minimal flat mapper
• TLB invalidation and mapping lifecycle need careful SMP handling

Implementation notes

• the first bring-up should prioritize early paging correctness, kernel map stability, and user-space address-space creation
• demand paging may be staged after initial static mapping support if needed for schedule control