“Linux frontman Linus Torvalds thinks he’s ‘more self-aware’ these days and is ‘trying to be less forceful’ after his brief absence from directing Linux kernel developers because of his abusive language on the Linux kernel mailing list,” reports ZDNet.
“But true to his word, he’s still not necessarily diplomatic in his communications with maintainers…”
Torvalds’ post-hiatus outburst was directed at Dave Chinner, an Australian programmer who maintains the Silicon Graphics (SGI)-created XFS file system supported by many Linux distros. “Bullshit, Dave,” Torvalds told Chinner on a mailing list. The comment from Chinner that triggered Torvalds’ rebuke was that “the page cache is still far, far slower than direct IO” — a problem Chinner thinks will become more apparent with the arrival of the newish storage-motherboard interface specification known as Peripheral Express Interconnect Express (PCIe) version 4.0. Chinner believes page cache might be necessary to support disk-based storage, but that it has a performance cost….
“You’ve made that claim before, and it’s been complete bullshit before too, and I’ve called you out on it then too,” wrote Torvalds. “Why do you continue to make this obviously garbage argument?” According to Torvalds, the page cache serves its correct purpose as a cache. “The key word in the ‘page cache’ name is ‘cache’,” wrote Torvalds…. “Caches work, Dave. Anybody who thinks caches don’t work is incompetent. 99 percent of all filesystem accesses are cached, and they never do any IO at all, and the page cache handles them beautifully,” Torvalds wrote.
“When you say the page cache is slower than direct IO, it’s because you don’t even see or care about the *fast* case. You only get involved once there is actual IO to be done.”
“The thing is,” reports the Register, “crucially, Chinner was talking in the context of specific IO requests that just don’t cache well, and noted that these inefficiencies could become more obvious as the deployment of PCIe 4.0-connected non-volatile storage memory spreads.”
Here’s how Chinner responded to Torvalds on the mailing list. “You’ve taken one single statement I made from a huge email about complexities in dealing with IO concurrency, the page cache and architectural flaws in the existing code, quoted it out of context, fabricated a completely new context and started ranting about how I know nothing about how caches or the page cache work.”
The Register notes their conversation also illustrates a crucial difference from closed-source software development. “[D]ue to the open nature of the Linux kernel, Linus’s rows and spats play out in public for everyone to see, and vultures like us to write up about.”