Linus Torvalds uses Claude Code for kernel patches; reviewer flags a race

In October 2026, Linus Torvalds, the creator of Linux and its long-time lead maintainer, turned to Anthropic's Claude Code to tackle a kernel performance problem that had dogged developers for more than two years. He submitted a series of 10 patches that remove folio reference counting operations from the common buffered read path. In synthetic benchmarks run on a Ryzen Threadripper, the series lifted read throughput by 23x, though Torvalds cautioned that the gain would be much smaller under real workloads. He had previously spent 18 months running a flawed fix of his own in an attempt to resolve a reference counting bottleneck in the page cache, and proposals from other developers had also run into problems.

Before the patches were merged, kernel reviewer Kiryl Shutsemau flagged a race condition in filemap_read_rcu_batch(): if a folio is replaced and the file size (i_size) is then extended, the read path could return data that has not yet been written to the file back to a user program. The reviewer also raised questions about the patch series' memory reclaim mechanism. Torvalds has handed further development to Shutsemau, who had also studied this bottleneck before.