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Virtual memory skill for paging, page tables, and TLB. Use when explaining page faults, multi-level page tables, TLB behavior, or virtual vs physical addressing. Activates on queries about virtual memory, page table, TLB, page fault, mmap paging, or x86-64 paging.
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基于 SOC 职业分类
| name | virtual-memory-paging-and-tlb |
| description | Virtual memory skill for paging, page tables, and TLB. Use when explaining page faults, multi-level page tables, TLB behavior, or virtual vs physical addressing. Activates on queries about virtual memory, page table, TLB, page fault, mmap paging, or x86-64 paging. |
Explain virtual memory: paging, multi-level page tables, TLB role, page faults, and address translation — bridging OS kernels, embedded MPU, and performance analysis.
mmap, brk, and demand pagingVirtual address (VA)
├── TLB lookup → physical on hit
└── TLB miss → page table walk → fill TLB
├── valid PTE → physical address
└── invalid → page fault (OS handles)
CR3 → PML4 → PDPT → PD → PT → physical frame
Linux on x86_64 uses 4 KiB pages (default) and optional 2 MiB / 1 GiB huge pages.
| Fault | Typical cause |
|---|---|
| Major | Disk read — file-backed page not in RAM |
| Minor | Zero-fill or COW break |
| Protection | User access to kernel page, W^X violation |
# Linux page fault stats
grep pgfault /proc/vmstat
Large sparse address spaces + random pointer chasing → TLB misses dominate.
Mitigations:
mmap huge pages (MAP_HUGETLB, madvise(MADV_HUGEPAGE))numactl --membind for NUMAMany MCUs use MPU (region-based) not full paging — no TLB, fixed region count. Application processors use MMU + OS.
See skills/platform/riscv-privileged for Sv39/Sv48.
cat /proc/self/maps
pmap -x $$
/virtual-memory-paging-and-tlb Explain why 4 KiB random access hurts TLB and hugepage helps
| Symptom | Cause | Fix |
|---|---|---|
| Segfault | Unmapped VA | Fix pointer; check maps |
| Slow mmap workload | TLB thrashing | Huge pages; reduce regions |
| COW spike after fork | Shared pages split on write | Expected; consider MAP_POPULATE |
| W^X fault | JIT without mprotect dance | Separate RW and RX mappings |
| Wrong phys on MCU | No MMU — linear map | Use linker script addresses |
skills/computer-architecture/memory-hierarchy-and-caches — cache after translationskills/kernel-dev/kernel-memory-management — kernel page allocatorskills/kernel/os-dev-scratch — build paging from scratchskills/platform/riscv-privileged — Sv39 page tablesskills/allocators/numa-programming — NUMA and migrationCustom allocator skill for memory allocation strategies. Use when implementing pool/slab/arena allocators, tuning jemalloc/mimalloc, writing Rust GlobalAlloc, or benchmarking allocator performance. Activates on queries about jemalloc, mimalloc, tcmalloc, arena allocator, GlobalAlloc, or fragmentation.
NUMA programming skill for multi-socket memory locality. Use when detecting NUMA topology, binding processes with numactl, using libnuma API, building NUMA-aware data structures, or measuring remote access penalties. Activates on queries about numactl, libnuma, NUMA topology, mbind, lstopo, or remote memory access.
AF_XDP skill for high-performance XDP sockets. Use when creating AF_XDP sockets, configuring UMEM and XSK rings, XDP_REDIRECT programs, copy vs zero-copy mode, or comparing with DPDK. Activates on queries about AF_XDP, xsk_umem, XDP_REDIRECT, libbpf xsk, or zero-copy XDP.
DPDK skill for userspace packet I/O. Use when initializing EAL, configuring PMD drivers, using mbuf pools and rte_ring, setting up huge pages, RSS, or testpmd validation. Activates on queries about DPDK, EAL, rte_eth_rx_burst, hugepages, PMD, or testpmd.
io_uring skill for Linux async I/O. Use when building high-performance servers with liburing, multi-shot operations, provided buffers, fixed files, zero-copy send, or tokio-uring. Activates on queries about io_uring, SQE/CQE, liburing, IORING_OP_PROVIDE_BUFFERS, or io_uring vs epoll.
Bare-metal ADC and DAC skill. Use when configuring analog sampling, DMA-driven ADC, calibration, or DAC output on MCUs. Activates on queries about ADC bare-metal, sampling time, DMA ADC, or DAC channel setup.