Zero-Copy Access Features

• Zero-copy access is a method enabling hardware and software agents to share memory directly without intermediate copies, critical for high-performance and real-time systems.
• Techniques like shared memory remapping, page table manipulation, and kernel-user interfaces deliver measurable latency reduction and throughput gains in various benchmarks.
• Challenges such as overhead from system calls, coordination of shared resources, and security limitations are mitigated through strategies like memory protection, ASLR, and cryptographic validations.

Zero-copy access refers to methods that allow different hardware or software agents—such as user processes, network devices, or accelerators—to access shared memory regions and exchange data without first copying that data into intermediate or temporary buffers. This capability is essential for high-performance computing, real-time data processing, large-scale machine learning, robotics IPC, and cloud-scale serverless architectures, where the cost of memory copies and serialization/deserialization forms a significant bottleneck. Zero-copy features typically exploit OS and hardware support for shared memory, direct device memory access (DMA), page table manipulation, or memory protection, while solving the correctness, coherence, and usability challenges inherent in these mechanisms.

1. Architectural Approaches to Zero-Copy Access

Intra-Process and Inter-Process Shared Memory

Approaches such as Agnocast transparently remap application heap allocations into a shared memory region using a fixed virtual address, facilitating pointer-level sharing of dynamically sized and statically sized data structures between publisher and subscriber processes; these eliminate serialization and all user-space copies, and crucially support unsized types (e.g., C++ STL vectors) via libc malloc/free interposition (Ishikawa-Aso et al., 20 Jun 2025).

Memory Protection and Page Table Manipulation

Memory-protection-based designs utilize virtual memory page tables to enforce temporal access control on buffers in flight—marking regions as read-only using OS mechanisms (mprotect) and intercepting writes via signal handlers (SIGSEGV) so that only one copy ever exists and unsafe accesses are automatically serialized. This approach provides transparent race prevention with non-blocking send/receive, at the cost of syscall and signal-handling overhead, and requires no per-access user code changes (Power, 2013).

Kernel-User Shared Memory and Sandboxed Access

SBPF establishes a cryptographically authorized, ASLR-randomized shared region between the kernel and userspace, accessed under control of a userspace-embedded BPF VM, with vDSO call wrappers for indirect function entry and hard-evaluated range checks to prevent out-of-bounds access and side-channel leakage. No copy_from_user/copy_to_user is required after the shared region is set up, and user-kernel round-trips for data are eliminated (Kong et al., 27 Jun 2025).

Cluster and Accelerator Coherence Domains

Cluster-wide zero-copy is realized by mapping columnar, immutable Arrow buffers over a cluster shared memory interconnect (e.g., ThymesisFlow/OpenCAPI) and enforcing global address alignment at mmap time. Local consistency in the absence of hardware global coherence is maintained by explicit cacheline invalidation at buffer publication. All subsequent accesses to the data across nodes are load/store at native speed, with only schema metadata serialized for discovery (Groet et al., 2024).

Network-Accelerated and Device-Led Zero-Copy

NIC offload solutions (sPIN) execute MPI-derived datatype unpack/pack routines as handlers on in-NIC processing cores. Data is DMA-ed directly to its final destination (potentially non-contiguous) in host address space, without staging or CPU-side copying. This supports both contiguous and complex, strided layouts at line rates, with generality traded off in favor of programmable handler cost for highly non-uniform types (Girolamo et al., 2019).

2. Methodologies and Workflow Integration

Approach	Granularity/Domain	Typical Integration Points
Memory-protection (mprotect)	Page, intra-process	Non-blocking send/receive
Shared-memory pointer cast	Heap, IPC, multimodal	Publish/subscribe, FaaS IPC
Kernel-user shared memory	Page/region	Custom system call interface
Cluster-shared memory	Buffer/region	Distributed table operations
NIC handler (sPIN)	Packet, MPI block	HPC datatype message passing

Zero-copy must be orchestrated with system APIs and workflows. Memory-protection approaches instrument non-blocking send/receive APIs (e.g., MPI_Isend) and rely on standard system calls for virtual memory protection and signal handling (Power, 2013). Shared-memory remapping for publish/subscribe (e.g., Agnocast, Zerrow, Bauplan) is integrated via programmatic hooks, API replacements, or LD_PRELOAD wrappers, with the bulk of changes confined to resource setup and teardown, not core application logic (Ishikawa-Aso et al., 20 Jun 2025, Tagliabue et al., 2024, Dai et al., 8 Apr 2025). Kernel-user models require trusted loader modules, capability gating, and cryptographic validation (SBPF) (Kong et al., 27 Jun 2025). Cluster-shared memory necessitates system-wide address mapping discipline, cross-process cache and TLB management, and cross-node orchestration of allocation and consistency (Groet et al., 2024). NIC handler-based methods require pre-registration of buffers and deployment of code stubs for message type-specific unpacking (Girolamo et al., 2019).

3. Performance Models and Empirical Results

Zero-copy features yield asymptotic improvements in latency and throughput, especially for large-message, high-bandwidth, or real-time use cases.

• Memory-protection zero-copy matches or exceeds line-rate for messages ≥4 KiB, with only rare page-fault overhead for writes that race in-flight sends. Application throughput matches that of non-blocking send + manual locking, but with reduced code complexity. For small messages (<256 B), syscall/signal costs dominate, so standard copying is superior (Power, 2013).
• In Agnocast, IPC latency is constant (~0.2 ms) across all message sizes and types, including unsized C++ vectors. Under CPU load, jitter (CV) remains <5%, compared to 20–50% for DDS/IceOryx. Real system benchmarks report 16–25% improvements in real-time Autoware pipelines by eliminating copy/serialization (Ishikawa-Aso et al., 20 Jun 2025).
• SBPF reduces user-kernel data path latencies, yielding macrobenchmark gains up to 12%, 4–8% syscall speedups, and 1.3–5.2× improvements in ringbuffer SPSC workloads (Kong et al., 27 Jun 2025).
• Cluster-shared-memory Arrow pipelines achieve creation latencies for 1 GiB tables of ~300 ms, with “effective transfer” limited to a few milliseconds for metadata only, and random access at 40–90% of local DRAM bandwidth. Overhead reductions vs. Ethernet-based copy are one to two orders of magnitude for real payloads (Groet et al., 2024).
• In Bauplan/Zerrow, single-node Arrow pipeline I/O time is reduced by 100–200× (0.01–0.03 s to read a 6–30 GB table), and memory is reduced from NxM to 1xM for N consumers; global DAG sharing and de-anonymization eliminate nearly all intermediate writes (Tagliabue et al., 2024, Dai et al., 8 Apr 2025).
• sPIN provides up to 10–12× speedup vs. host-side unpack for non-contiguous messages, and 26% reduction in end-to-end communication time in realistic FFT2d workflows (Girolamo et al., 2019).

4. Correctness, Security, and Limitations

Zero-copy systems address correctness and safety with a combination of hardware isolation, OS permission enforcement, and execution sandboxing:

• Memory-protection solutions depend on page-level isolation. The granularity induces false positives, blocking logically non-overlapping accesses, and exposes performance to TLB shootdown and signal costs (Power, 2013).
• Shared heap models (Agnocast, Bauplan, Zerrow) depend on the application avoiding modification of shared pages after publication (immutability for Arrow); mechanisms such as SIPC and KernelZero enforce page remapping and, optionally, write revocation. Partial-page and alignment mismatches may still induce residual copy on unaligned boundaries (Dai et al., 8 Apr 2025).
• Kernel-user approaches require in-kernel verifiers (SBPF/eBPF), cryptographic validation of userspace libraries, and per-process capability gating to provide vulnerability boundaries, as well as execute-only vDSO and ASLR to resist guess-based attacks (Kong et al., 27 Jun 2025).
• Cluster-wide schemes can only avoid coherence races if data is published as strictly immutable; updates after mapping require explicit cacheline invalidation and may not be safe without strong memory ordering (Groet et al., 2024).
• sPIN and device-offload designs must manage in-NIC buffer exhaustion, register all target memory for DMA, and orchestrate checkpoint/accounting for complex datatype unpacking, as well as provide MMU-boundaries to prevent DMA outside registered buffers (Girolamo et al., 2019).

5. Use Cases across Domains

Zero-copy access features are exploited in a wide array of systems:

• HPC message passing (MPI), with hardware-enabled DMA directly into user buffers and offloaded MPI datatype support (Power, 2013, Girolamo et al., 2019).
• Robotics IPC and middleware (ROS 2, Agnocast), where zero-copy is critical for large unsized sensor messages in real-time perception and control (Ishikawa-Aso et al., 20 Jun 2025).
• Serverless and data pipeline engines (Bauplan, Zerrow, Palladium) for cloud-scale analytics/FaaS, where zero-copy minimizes data movement through shared Arrow tables or RDMA-based buffer sharing, enabling DAGs and pipelines to meet interactive and cost-sensitive SLAs (Tagliabue et al., 2024, Dai et al., 8 Apr 2025, Qi et al., 16 May 2025).
• Kernel-user API acceleration (SBPF), reducing cost of system call data paths, kernel→user notifications, and ringbuffer-based communication (Kong et al., 27 Jun 2025).
• Distributed database and analytics SQL engines, using cluster-coherent Arrow memory to achieve inter-node dataflow at memory speed (Groet et al., 2024).
• Host-NDA cooperative acceleration for ML and data streaming, directly sharing DRAM buffers in near-data accelerator architectures (Cho et al., 2019).
• GNN training systems for direct host-GPU memory access to sparse feature arrays, saturating PCIe bandwidth with no CPU-side staging (Min et al., 2021).

6. Trade-offs, Challenges, and Future Directions

While zero-copy access unlocks peak bandwidth and minimal processing latency, it exposes practical and theoretical limits:

• Overhead of system calls and page-fault/signal handling for small data units, requiring hybrid schemes (dynamic thresholds for copy vs. zero-copy) (Power, 2013).
• Page granularity in protection and sharing leads to internal fragmentation and potentially superfluous stalling (Power, 2013, Dai et al., 8 Apr 2025).
• Need for global coordination of address mappings, base addresses, or resource handles across distributed systems (Groet et al., 2024, Ishikawa-Aso et al., 20 Jun 2025).
• Security and trust limitations in kernel-user sharing; focus on formal modeling, verifier hardening, and ASLR/enclave approaches to avoid privilege escalation (Kong et al., 27 Jun 2025).
• Incomplete kernel support for anonymous-file page remapping, only partially resolved by custom kernel modules (KernelZero) or in-development primitives (process_vm_mmap, msharefs) (Dai et al., 8 Apr 2025).
• Edge-case copy fallback for unaligned ranges, partial pages, or non-immutable data (Dai et al., 8 Apr 2025).
• Potential for resource contention or memory exhaustion (e.g., NIC memory for in-flight packets or cluster-region allocation hotspots) (Groet et al., 2024, Girolamo et al., 2019).
• Need for explicit data publication/synchronization points to ensure readers see stable views: unaddressed, this can lead to data races or exposure of dirty buffers.

Ongoing research is focused on extending formal correctness guarantees (e.g., capability types for offset accounting), integrating primitives into mainline Linux, and further reducing alignment-, granularity-, and security-induced overheads. Extensions to the JVM, Rust, and other managed runtimes are a topic of active work (Dai et al., 8 Apr 2025). Advances in device-centric NDAs, PCIe/CXL shared-memory capability, user-level paging, and unified endpoint security models are anticipated to further broaden zero-copy applicability.