Linus Torvalds uses the AI assistant Claude Code to prepare a Linux kernel improvement

Linus Torvalds, the creator of Linux, has acknowledged in writing, in a message dated Saturday, October 10, that he used AI to prepare a kernel improvement.

Torvalds has opened a branch in his main repository, named noref-filemap-read-with-llm, with a proposal for the kernel page cache (the memory where Linux keeps file data). The goal is to reduce contention when many threads make small reads from the same file, a problem that, according to the message that accompanies the branch, was already raised in 2024 from a customer workload. At present every read takes and drops a reference on the page it reads, and threads compete for that counter. The proposal allows reading without that reference and, in exchange, delays the release of memory that leaves the cache.

According to that text, the code, the test programs, the review behind its list of problems and the first draft of the message itself were done with Claude Code, an AI coding assistant, "under my direction". The measurements, he adds, were run on his machine.

The measurements were run only on his laptop, a machine with a processor of 4 cores and 8 threads. With eight threads reading 16 bytes of the same file at once, the cost of each read in the kernel drops from between 2,937 and 2,975 processor cycles to 725 or 726. Torvalds expects a machine with more processors to gain more, but notes that nothing bigger has been measured. Not everything improves: a read into a page of program memory that is not yet present costs one extra failed exception per read.

The message also lists ten known problems or points on which he asks others to look. Among them: the memory allocator cannot see the pages waiting to be freed, which in one test ran a virtual machine out of memory (the last two patches in the series avoid it in that test, without solving the underlying issue); a regression in contiguous memory allocation (CMA) as the series stands; and the cost outside the read path has not been measured. It has not been tested on any other machine either, nor with several of the usual kernel verification tools, such as xfstests, lockdep or KASAN.

The Phoronix website, which spotted the branch while waiting for the release of Linux 7.3-rc7, notes that Torvalds does not usually work on branches in his main repository, where he typically hosts only the master branch, and recalls that he had already used AI to help debug the kernel and, outside it, to program with Antigravity, from Google. According to Phoronix, it remains to be seen whether the branch is merged in the Linux 7.4 merge window. The series, of eight patches, is based on version 7.3-rc6 of the kernel plus fixes.