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Architecture Memory EN
Language: English ｜ Architecture-Memory
kernel/mem/mem_pmm.{c,h}: a bitmap over 4 KiB page frames built
from the multiboot2 memory map. Reserved regions (kernel image,
framebuffer, the mbi itself) are marked used at init. O(1) alloc and
free. memtest / pmmrace exercise it in-guest.
kernel/mem/mem_vmm.{c,h}: the kernel keeps boot.S's identity map of
the low 4 GiB; VMM creates and edits additional address spaces for
user processes. Protection flags map to read/write/nx/user bits.
vmtest, vmmap, vmkernelpt, cr3test inspect it live.
kernel/mem/mem_heap.{c,h}: free-list, first-fit, coalescing; blocks
are 16-byte aligned (the header is exactly 32 bytes - a historical
alternating-parity bug made payload alignment depend on allocation
parity, which then shifted ATA-DMA PRDT windows and broke FAT32
mounts; the header size is now static-asserted). 16 MiB fail-fast
ceiling; heaptest + heapbounds are the tests, heap/frag the
inspectors.
Stack-growth and heap-growth #PF are handled in the exception path:
a fault below a task's stack pointer within its stack region maps a
new page; heap growth maps backing pages; anything else escalates to
the crash path. exc proves the trap machinery each boot.
Drivers that program physical addresses into device structures validate alignment and, for 32-bit DMA masks, that the address is below 4 GiB (xHCI refuses above-4GiB DMA at probe AND per-transfer; ATA-DMA masks the PRDT). This is why the heap's alignment guarantees are load-bearing.