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The kernel's slab allocator is charged with providing small objects on demand; its performance and reliability are crucial for the functioning of the system as a whole. At the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit, two adjacent sessions in the memory-management track dug into current work on the slab allocator. The first focused on the new sheaves feature, while the second discussed a set of allocation functions that are safe to call in any context.

From the LibreQoS site comes the sad news that Dave Täht has passed away. Among many other things, he bears a lot of credit for our networks functioning as well as they do. "We're incredibly grateful to have Dave as our friend, mentor, and as someone who continuously inspired us – showing us that we could do better for each other in the world, and leverage technology to make that happen. He will be dearly missed".

Searching through LWN's archives will turn up many references to his work fixing WiFi, improving queue management, tackling bufferbloat, and more. Farewell, Dave, we hope the music is good wherever you are.

(Thanks to Jon Masters for the heads-up).

As he has in some previous editions of the Linux Storage, Filesystem, Memory-Management, and BPF Summit (LSFMM+BPF), Fred Knight gave an update on the status of various storage standards this year. In it, he looked at changes to the NVM Express (NVMe) standards in some detail. He also updated attendees on the fairly small changes that have come to the SCSI (T10) and ATA (T13) standards over the last few years.

The kernel's kexec mechanism allows one kernel to directly boot a new one; it can be thought of as a sort of kernel equivalent to the execve() system call. Kexec has a number of uses, including booting a special kernel to perform dumps after a crash. Normally, one does not expect user-space processes to survive booting into a new kernel, but that has not stopped developers from trying to implement that ability. Mike Rapoport ran a memory-management-track session at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit to discuss one piece of that problem: enabling the contents of memory to persist across a kexec handover so that the new kernel can pick up where the old one left off.

Version 137.0 of the Firefox browser has been released. Changes include the rollout of tab groups, a number of search-bar changes, and the ability to add signatures to PDF files.

Security updates have been issued by AlmaLinux (freetype, grub2, kernel, kernel-rt, and python-jinja2), Debian (freetype, linux-6.1, suricata, tzdata, and varnish), Fedora (mingw-libxslt and qgis), Mageia (elfutils, mercurial, and zvbi), Oracle (grafana, kernel, libxslt, nginx:1.22, and postgresql:12), Red Hat (opentelemetry-collector), SUSE (corosync, opera, and restic), and Ubuntu (aom, libtar, mariadb, ovn, php7.4, php8.1, php8.3, rabbitmq-server, and webkit2gtk).

The virtual memory area (VMA), represented by struct vm_area_struct, is one of the core abstractions of the kernel's memory-management subsystem; a VMA represents a portion of a process's address space with the same characteristics. A memory-mapped file will be represented by (at least) one VMA, as will the process's stack or a region of anonymous memory. Efficiently managing VMAs and the logic around them is crucial for good performance overall. Lorenzo Stoakes focused on one specific problem area: the merging of anonymous VMAs, during the memory-management track at the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit.

Migration is the act of moving data from one location in physical memory to another. The kernel may migrate pages for many reasons, including defragmentation, improving NUMA locality, moving data to or from memory hosted on a peripheral device, or freeing a range of memory for other uses. Given the importance of migration to the memory-management subsystem, there is a lot of interest in improving its performance and removing impediments to its success. Several sessions in the memory-management track of the 2025 Linux Storage, Filesystem, Memory-Management, and BPF Summit were dedicated to this topic.

The effort to ensure that open-source software is reproducible has been gathering steam over the years, and gaining traction with major Linux distributions. Debian, for example, has been working toward reproducible builds for more than a decade; it can now produce official live CDs of the current stable release that are reproducible. Fedora started on the path much later, but it has progressed far enough that the project is now considering a change proposal for the Fedora 43 development cycle, expected to be released in October, with a goal of making 99% of Fedora's package builds reproducible. So far, reaction to the proposal seems favorable and focused primarily on how to achieve the goal—with minimal pain for packagers—rather than whether to attempt it.

Security updates have been issued by Debian (amd64-microcode, flatpak, intel-microcode, libdata-entropy-perl, librabbitmq, and vim), Fedora (augeas, containerd, crosswords-puzzle-sets-xword-dl, libssh2, libxml2, nodejs-nodemon, and webkitgtk), Red Hat (libreoffice and python-jinja2), SUSE (389-ds, apparmor, corosync, docker, docker-stable, erlang26, exim, ffmpeg-4, govulncheck-vulndb, istioctl, matrix-synapse, mercurial, openvpn, python3, rke2, and skopeo), and Ubuntu (ansible, linux, linux-hwe-5.4, linux-azure, linux-azure-5.4, linux-bluefield, linux-gcp, linux-gcp-5.4, linux-ibm, linux-kvm, linux-oracle, linux-oracle-5.4, linux-xilinx-zynqmp, linux-azure-fips, linux-gcp-fips, linux-fips, linux-fips, linux-aws-fips, linux-azure-fips, linux-gcp-fips, linux-nvidia-tegra, linux-nvidia-tegra-igx, linux-realtime, linux-intel-iot-realtime, linux-xilinx-zynqmp, opensc, and ruby-doorkeeper).

Greg Kroah-Hartman announced the release of four stable kernels on March 28: 6.13.9, 6.12.21, 6.6.85, and 6.1.132. Users are advised to upgrade.

KDE contributor David Edmundson has published a blog post about improving KDE Plasma's login experience by replacing SDDM with a new Plasma Login Manager.

It's worth stressing nothing is official or set in stone yet, whilst it has come up in previous Plasma online meetings and in the 2023 Akademy. I'm posting this whilst starting a more official discussion on the plasma-devel mailing list.

Oliver Beard and I have made a new mutli-process greeter, that uses the same startup mechanism as the desktop session. It doesn't have all the features that we propose at the start of the blog, but an architecture where features and services can be slowly and safely added.

That discussion is here for those who would like to follow along. The prototype is currently in two repositories: plasma-login for the frontend work, and plasma-login-manager, which is a fork of SDDM.

In a keynote on the final day of SCALE 22x, Denver Gingerich said that he wanted to talk "a little bit about a router and also the big picture around that router". Gingerich is the director of compliance at the Software Freedom Conservancy (SFC), which is the organization behind the OpenWrt One router that LWN looked at back in November. The router is, of course, based on firmware from the OpenWrt project, which got its start because of GPL-enforcement activities and is a member project at the SFC.

As of this writing, 6,653 non-merge changesets have been pulled into the mainline kernel repository for the 6.15 release. This merge window is thus well underway. A number of significant changes have been merged so far; read on for our summary of the first half of the 6.15 merge window.

Security updates have been issued by Debian (mercurial and opensaml), Fedora (augeas, mingw-libxslt, and nodejs-nodemon), Mageia (chromium-browser-stable), Red Hat (grafana, kernel, kernel-rt, opentelemetry-collector, and podman), SUSE (apache-commons-vfs2, python3, and python36), and Ubuntu (ghostscript, linux, linux-aws, linux-azure, linux-gcp, linux-gke, linux-gkeop, linux-ibm, linux-intel-iotg, linux-lowlatency, linux-lowlatency-hwe-5.15, linux-nvidia, linux-oracle, linux-oracle-5.15, linux-raspi, linux, linux-aws, linux-azure, linux-gcp, linux-hwe-6.11, linux-oracle, linux-realtime, linux, linux-aws, linux-gcp, linux-gcp-6.8, linux-gke, linux-gkeop, linux-lowlatency, linux-lowlatency-hwe-6.8, linux-nvidia, linux-nvidia-6.8, linux-nvidia-lowlatency, linux-oracle, linux-oracle-6.8, linux-aws-5.15, linux-kvm, linux-azure, linux-ibm, linux-lowlatency, linux-lowlatency-hwe-6.11, linux-oem-6.11, linux-oem-6.8, linux-realtime, smarty, and snakeyaml).

Ubuntu 23.10 and 24.04 LTS introduced a feature using AppArmor to restrict access to user namespaces. Qualys has reported three ways to bypass AppArmor's restrictions and enable local users to gain full administrative capabilities within a user namespace. Ubuntu has followed up with a post that explains the namespace-restriction feature in detail, and says these bypasses do not constitute security vulnerabilities.

While a superficial observation of the application of user namespaces may indicate privileged (root level) access, this is a fictitious state that is operating as expected, with access control still mapped to the real (root namespace) user's permissions. As such, these bypasses do not enable more access than what the default Linux kernel unprivileged user namespace feature allows in most Linux distributions. They do, however, demonstrate limitations that we are looking to address in order to strengthen existing protections against as-of-yet-unknown Linux kernel vulnerabilities.

LWN covered Ubuntu 24.04 LTS last May.

One recurring criticism of Rust has been that the language has no official specification. This is a barrier to adoption in some safety-conscious organizations, as well as to writing alternate language implementations. Now, the Rust project has announced that it will be adopting the Ferrocene Language Specification (FLS) developed by Ferrous Systems and maintaining it as part of the core project. While this may not satisfy die-hard standardization-process enthusiasts, it's a step toward removing another barrier to using Rust in safety-critical systems.

It's in that light that we're pleased to announce that we'll be adopting the FLS into the Rust Project as part of our ongoing specification efforts. This adoption is being made possible by the gracious donation of the FLS by Ferrous Systems. We're grateful to them for the work they've done in assembling the FLS, in making it fit for qualification purposes, in promoting its use and the use of Rust generally in safety-critical industries, and now, for working with us to take the next step and to bring the FLS into the Project.

Arthur Cohen has posted a massive series of patches in four parts (part 1, part 2, part 3, part 4) upstreaming all of the recent work on the GCC Rust front end. These changes include the Polonius borrow checker, the foreign-function interface, inline assembly support, if-let statement handling, multiple built-in derive macros, for loops, and more.

The 2024 Linux Storage, Filesystem, Memory-Management, and BPF Summit included a tense session on the use of Rust code in the kernel's filesystem layer. The Rust topic returned in 2025 in a session run by Andreas Hindborg, with a scope that also covered the storage and memory-management layers. A lot of progress has been made, and the discussion was less adversarial this year, but there are still process issues that need to be worked out.

Security updates have been issued by Arch Linux (exim), Debian (exim4, ghostscript, and libcap2), Red Hat (container-tools:rhel8), SUSE (apache-commons-vfs2, argocd-cli, azure-cli-core, buildah, chromedriver, docker-stable, ed25519-java, kernel, kubernetes1.29-apiserver, kubernetes1.30-apiserver, kubernetes1.32-apiserver, libmbedcrypto7, microcode_ctl, php7, podman, proftpd, tomcat10, and webkit2gtk3), and Ubuntu (containerd, exim4, mariadb, opensaml, and org-mode).