L inus Torvalds announced the seventh (and likely final) Release Candidate for what will be Linux 6.14. As we covered during the merge window (period of early development when disruptive changes land), the new kernel includes driver enhancements, particularly for AMD GPUs and AI-related integrated NPUs. It also includes the new ntsync driver to speed up Windows emulation in Wine. In fact, a late breaking development on the latter identified that it was by default only available to the root user, prior to a trivial one-liner patch that changes permissions on the device file used to access it.
Kernel Samepage Merging
The kernel (optionally) includes a feature known as Kernel Samepage Merging (KSM). It is traditionally used by KVM (Kernel Virtual Machine), the in-kernel hypervisor, to detect when pages (the unit of memory management) of guest VM memory are identical and replace those with a single read-only copy (which is then split out again transparently if either guest modifies their version). This can save considerable host memory when running a lot of similar or identical VMs, but (as noted in the discussion) it also introduces security risks when hosting third-party VMs. KSM uses an in-kernel scanner that walks guest memory brute-force searching for matches, using quite invasive code in the process.
Mathieu Desnoyers proposes a much simpler Synchronous KSM in which userspace annotates opportunities for merging. Linus said he was “not interested in seeing another KSM version” since he had seen that with memory allocators in the past (SLUB versus SLAB versus SLOB, and so on) and didn’t want years of wrangling ahead. He preferred the idea of a replacement if that were possible, given that “our current KSM model has largely been a failure, and this might be ‘good enough’”. Mathieu ultimately proposed a userspace daemon that could use a simpler kernel API to implement much of the existing KSM logic.