TL;DR
Microsoft has merged a change in WSL 2 that assigns dedicated DMA pools to each virtio device, reducing contention and improving file I/O performance. This update benefits users with cross-OS workflows involving heavy file operations.
Microsoft has implemented a significant performance improvement in WSL 2 by assigning each virtio device its own dedicated DMA pool, reducing contention and boosting file system access speeds for cross-OS workflows.
This change was merged into WSL 2 in May 2026 as part of ongoing efforts to optimize cross-OS file access. Prior to this update, all virtio devices shared a single DMA buffer, which caused contention during heavy I/O operations, especially with multiple devices such as drives and network adapters.
The update involves the Linux kernel reading specific sysfs entries to allocate a contiguous physical memory region below the 4 GB boundary for each device at boot time. These dedicated pools are then injected into each virtio device during creation, eliminating the previous shared buffer contention.
This enhancement requires the latest WSL kernel, specifically Microsoft.WSL.Kernel 6.18.26.3-1, and the WSL 2 DeviceHost 1.2.29-0. Without this kernel, WSL will notify users that their kernel lacks the necessary patch for improved virtio device performance.
Why It Matters
This development matters because it directly improves performance for developers and users who rely on cross-OS workflows involving large file operations. Tasks like building code, installing packages, or managing repositories across Windows and Linux partitions will see reduced latency and faster throughput, especially on workloads that involve numerous small file operations.
By reducing contention at the DMA layer, this update also benefits network performance and other virtual device interactions, making WSL 2 a more efficient environment for development, testing, and deployment workflows that span both operating systems.
WSL 2 compatible Linux kernel
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Background
Since its initial release in 2016, WSL has evolved from relying on DrvFs for Windows drive access to implementing a full Linux kernel in WSL 2, which introduced a VM boundary. Over time, Microsoft has improved cross-OS file access performance, moving from 9P protocol overhead to experimental virtiofs support in 2021. The recent change marks the latest step in optimizing this pathway by addressing DMA contention, a known bottleneck since virtiofs’s inception.
Previous improvements included device reuse and shared mmap support, but the shared DMA buffer remained a limiting factor during intensive I/O tasks. The new per-device DMA pool allocation aims to mitigate this issue, aligning with Microsoft’s ongoing efforts to enhance WSL’s performance.
“The new DMA pool allocation for each virtio device removes a major contention point, significantly improving file I/O performance.”
— Microsoft WSL Development Team
“This update involves reading sysfs entries to allocate dedicated physical memory pools during kernel boot, which are then assigned to each virtio device at creation.”
— Ben Hillis, WSL Kernel Developer
high performance SSD for cross-OS workflows
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What Remains Unclear
It is not yet clear how widely this update will impact performance in real-world scenarios across different hardware configurations. Additionally, it remains to be seen when the default transport will switch from Plan 9 over Hyper-V socket to virtiofs, which is still opt-in.
virtio device performance upgrade
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What’s Next
Microsoft is expected to continue refining virtiofs support and possibly enable default use of virtiofs in future WSL updates. Users should update to the latest kernel and WSL version to benefit from these improvements. Further performance benchmarks and user feedback will clarify the real-world impact of these changes.
Windows Linux file system acceleration
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Key Questions
What is the main benefit of this DMA pool change in WSL 2?
It reduces contention among virtio devices during heavy I/O, leading to faster cross-OS file access and improved overall performance.
Do I need to do anything to enable this feature?
Yes, you should update to the latest WSL kernel with wsl.exe –update –pre-release and set virtiofs=true in your .wslconfig. Also, ensure your WSL 2 RAM allocation is above 1 GB for optimal performance.
Is virtiofs now the default transport for WSL 2?
No, virtiofs remains opt-in; the default transport is still Plan 9 over Hyper-V socket. Microsoft may change this in future updates.
Will this change affect all WSL users?
This update primarily benefits users with file-heavy workflows crossing Windows and Linux, especially those involving multiple virtio devices. Impact may vary based on individual workloads and hardware.
Source: Hacker News
