Significant ongoing work is happening to support CXL (Compute eXpress Link), which supports more contemporary mechanisms for attaching IO devices to modern systems. Among its various modes, the most popular is .mem (CXL.mem), which effectively allows for serial-attached memory modules much like PCIe plug-in cards as an alternative to DDR. While it won’t replace the bandwidth and latency characteristics of DDR any time soon, CXL.mem is growing in popularity as an additional tier of memory within very large systems. The ongoing work includes updated patches to support new system calls (mempolicy, mbind and so on) intended to improve bandwidth utilisation for processes using CXL memory.
“Additional uses for kexec have emerged, including that of live updating machines without a reboot.”
Alex Graf posted some really nice looking patches titled “kexec: Allow preservation of ftrace buffers”. Kexec is a lightweight mechanism used by Linux to chainload a secondary kernel, originally for debug purposes during a system rash (crashdump). Over time, additional uses for kexec have emerged, including that of live updating machines without a reboot. While we have tools like live kernel patching, this is mostly limited to small(ish) fixes. There are cases where one might want to update – as Alex cites by way of example – a host machine running virtualisation without tearing down the guest VM instances. His patches don’t (yet) go that far, but they do intend to. He starts with a fairly innocuous (and thus uncontentious) example of passing ftrace buffers on to the new kernel, but he plans to continue, citing a talk he co-presented with James Bottomley at the recent Linux Plumbers Conference (now online).
Sunny retirement
Finally this month, continued discussion of the removal of legacy architectures now touches the original 32-bit SPARC (but not the 64-bit architecture SPARC64 that is still in production), where it is intended to rip out support for sun4m and sun4d machines. As usual, this author is now feeling renewed pressure to finally ewaste some very old machines at home that haven’t been powered on in the better part of several decades.