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Linux Systems Field Manual

Final Synthesis

Imported from _research/manual-study-linux/final-synthesis.md.

Linux Manual Study Final Synthesis

Status: scheduler/process lifecycle and core memory-management volumes implemented; remaining volumes are VFS/filesystems, synchronization/RCU/locking, drivers/device model, security/isolation, and the broader Rust kernel layer.

The clean study baseline is repositories/reference/linux-study-clean at commit 1dc18801b.

The dossier now has reviewed notes for:

  • rust/kernel/lib.rs
  • rust/kernel/sync/arc.rs
  • rust/kernel/task.rs
  • kernel/fork.c
  • Documentation/process/coding-assistants.rst
  • kernel/sched/sched.h
  • kernel/sched/core.c
  • kernel/sched/fair.c
  • kernel/sched/rt.c
  • kernel/sched/deadline.c
  • Documentation/scheduler/sched-design-CFS.rst
  • Documentation/scheduler/sched-eevdf.rst
  • Documentation/scheduler/sched-rt-group.rst
  • Documentation/scheduler/sched-deadline.rst
  • include/linux/mm_types.h
  • include/linux/mm.h
  • mm/memory.c
  • mm/slab_common.c
  • Documentation/admin-guide/mm/concepts.rst
  • Documentation/core-api/memory-allocation.rst

Current conclusion: Linux-like Rust systems need typed membranes, staged lifecycles, and explicit scheduler policy boundaries. The in-kernel Rust surface avoids raw C API sprawl through a central wrapper crate; ownership is split into borrowed, unique, and shared pinned states; current task authority is scoped separately from durable task references; process creation is a staged pipeline; and scheduling is a per-CPU runqueue system whose policies are factored through class operation tables.

The scheduler volume shows how implementation detail matters. Linux does not have one generic “task queue.” It has per-CPU struct rq state, lock ordering, class-specific embedded queues, fork-time scheduler setup, first wakeup publication, preemption-aware scheduling loops, explicit context-switch phases, and different data structures for fair/EEVDF, RT, and deadline classes. A Rust equivalent should preserve those boundaries with typed guards, phase-specific task states, validated reservation objects, and a narrow unsafe architecture switch boundary.

The memory volume adds the second major lesson: Linux does not treat memory as a flat heap. It separates address spaces, VMAs, fault contexts, page-table levels, folios/pages, fault result bitmasks, and allocator caches. Page faults are typed control flow with retry/drop-lock behavior, race rechecks, COW copying, anonymous zero-page optimization, file-backed callbacks, and explicit PTE installation. A Rust equivalent needs typed fault states and page-table guards, not a single unsafe memory function.

For AI-native systems, the scheduler and memory lessons are direct: agent jobs need structured runqueues, class policies, budgets, deadlines, admission checks, tracepoints, and provenance. Agent state needs region permissions, lazy materialization, copy-on-write, typed fault outcomes, and allocator classes for repeated runtime objects.

Next synthesis target: VFS/filesystems, starting from fs/open.c, fs/read_write.c, include/linux/fs.h, and VFS documentation.