CXL (Compute Express Link) enables multiple hosts to share byte-addressable memory with hardware cache coherence, but no existing filesystem exploits this for lock-free multi-host coordination. We present DaxFS, a Linux filesystem for CXL shared memory that uses cmpxchg atomic operations, which CXL makes coherent across host boundaries, as its sole coordination primitive. A CAS-based hash overlay enables lock-free concurrent writes from multiple hosts without any centralized coordinator. A cooperative shared page cache with a novel multi-host clock eviction algorithm (MH-clock) provides demand-paged caching in shared DAX memory, with fully decentralized victim selection via cmpxchg. We validate multi-host correctness using QEMU-emulated CXL 3.0, where two virtual hosts share a memory region with TCP-forwarded atomics. Under cross-host contention, DaxFS maintains >99% CAS accuracy with no lost updates. On single-host DRAM-backed DAX, DaxFS exceeds tmpfs throughput across all write workloads, achieving up to 2.68x higher random write throughput with 4 threads and 1.18x higher random read throughput at 64 KB. Preliminary GPU microbenchmarks show that the cmpxchg-based design extends to GPU threads performing page cache operations at PCIe 5.0 bandwidth limits.

翻译：CXL（Compute Express Link）使多主机能够通过硬件缓存一致性共享字节可寻址内存，但现有文件系统并未利用这一特性实现无锁多主机协调。我们提出DaxFS——一个面向CXL共享内存的Linux文件系统，它以cmpxchg原子操作（CXL使其在跨主机边界保持一致性）作为唯一协调原语。基于CAS的哈希覆盖层支持多主机无锁并发写入，无需任何集中式协调器。一种协作式共享页面缓存配合新型多主机时钟替换算法（MH-clock），可在共享DAX内存中实现按需分页缓存，并通过cmpxchg实现完全去中心化的牺牲页选择。我们利用QEMU模拟的CXL 3.0验证多主机正确性，其中两个虚机共享一个内存区域，并通过TCP转发原子操作。在跨主机竞争场景下，DaxFS保持>99%的CAS正确率且无更新丢失。在单主机DRAM支撑的DAX环境中，DaxFS在所有写入负载下均超越tmpfs吞吐量：4线程随机写入吞吐量最高可达tmpfs的2.68倍，64KB随机读取吞吐量达1.18倍。初步GPU微基准测试表明，基于cmpxchg的设计可扩展至GPU线程，使其在PCIe 5.0带宽极限下执行页面缓存操作。