Discover dm-pcache, Linux’s new persistent memory cache for block devices—offering lower latency, DAX-optimized PMEM support & crash-safe replay. Learn how it outperforms BCache & dm-writecache for high-performance workloads.
The Linux kernel is set to gain a powerful new persistent memory cache solution with dm-pcache, a high-performance block-layer caching system evolved from the earlier PCACHE proposal.
Designed to outperform existing solutions like BCache and dm-writecache, this Device Mapper (DM)-based framework promises lower latency, greater concurrency, and superior integrity—making it ideal for enterprise storage, databases, and high-throughput workloads.
Why dm-pcache Stands Out in Linux Block Caching
Originally introduced as PCACHE in April, this persistent memory (PMEM) cache has been refactored into the Device Mapper subsystem, broadening its compatibility and ease of deployment. Key advantages over legacy solutions include:
✅ Ultra-low write latency via DAX-optimized PMEM
✅ Read cache support (unlike dm-writecache)
✅ High parallelism via multi-subtree RB-tree indexing
✅ Crash-safe replay with key-tail scanning for recovery
✅ Background write-back & garbage collection for sustained performance
Technical Deep Dive: How dm-pcache Works
16 MiB PMEM Segments: Log-structured allocation for efficient writes.
Data Integrity: Optional CRC32 checksums per cache entry.
Scalable Architecture: Optimized for multi-core systems with lock-free structures.
Write-Back Mode: Currently FIFO eviction, with LRU/ARC planned.
"dm-pcache could redefine how Linux handles block caching, particularly for NVMe and CXL-attached storage."
Current Limitations & Future Roadmap
While dm-pcache is already compelling, the RFC v2 patches highlight areas for improvement:
⚠ Only write-back mode is implemented (write-through coming later).
⚠ FIFO cache invalidation is the sole method—more adaptive policies (LRU, ARC) are in development.
For developers and sysadmins, this means dm-pcache is already viable for write-heavy workloads, with future updates poised to enhance read optimization.
Who Should Consider dm-pcache?
Database admins (PostgreSQL, MySQL on PMEM)
Cloud storage providers optimizing for CXL/NVMe
Enterprise IT teams deploying low-latency caching tiers
Final Thoughts: A Game-Changer for Persistent Caching?
With dm-pcache, Linux gains a modern, PMEM-aware caching layer that bridges the gap between volatile caches and slow block devices.
As CXL and Optane Persistent Memory adoption grows, this could become the default choice for high-performance storage stacks.
Want to test dm-pcache? The RFC v2 patches are now live for review and experimentation.
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