Linus Torvalds let Claude Code fix the Linux page cache. Then reviewers found a race.

Linus Torvalds, creator of the Linux kernel, enlisted the help of Anthropic’s Claude Code to address a performance issue with the page cache that had persisted for over two years. After 18 months of Torvalds running a flawed version of his own fix, other developers encountered similar challenges. The new patches eliminate folio reference-count operations from a common buffered-read path, though Torvalds noted that real-world performance gains would be smaller.

However, reviewers uncovered a race condition and raised concerns about memory reclamation. Torvalds handed further development to Kiryl Shutsemau, a Linux kernel developer who had previously worked on the same bottleneck. The issue of page cache contention was identified by Matthew Wilcox, an Oracle engineer and Linux kernel memory-management developer, in a customer workload.

Claude Code generated the patches, which were later reviewed by Torvalds. These patches resulted in substantial performance improvements in synthetic benchmarks, with throughput increasing by a factor of 23 on Torvalds’ Ryzen Threadripper. In a heavy contention scenario on a 64-thread Threadripper, throughput surged from 13.3 million to 304 million reads per second.

Despite the performance gains, the patches introduced trade-offs, such as increased kernel cycles per read and potential regressions in certain scenarios.