Memory Management

Memory Management

NyxOS uses a layered memory strategy: bitmap physical allocator, 4-level paging, kernel heap, and slab caches.

See also: Architecture, Boot Process, Process Management, Security

Physical allocator (memory.c)

Bitmap tracking each 4 KB page, up to 512 MB max RAM. alloc_page() / free_page().

4-level paging (paging.c)

PML4 → PDPT → PD → PT → 4 KB page. Higher-half kernel at PML4[511]. Identity-mapped first 64 MB.

• Demand paging: PTE bit 9 (PTE_DEMAND) — allocate zeroed page on first touch via #PF handler
• Copy-on-write: PTE bit 10 (PTE_COW) — private copy on write fault via #PF handler (used by fork(), see Process Management)
• NX bit: Non-executable user stack/data pages
• CR0.WP: Supervisor writes to read-only pages fault (required for COW)

Kernel heap (heap.c)

16 MB heap with free-list, header/footer metadata, coalescing. kmalloc/kfree with slab fallback.

Slab allocator (slab.c)

Fixed-size caches: 8, 16, 32, 64, 128, 256, 512, 1024 bytes.