The problem of negative dentries accumulating in the dentry cache in an unbounded manner, as we looked at back in April, came up at the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM). Negative dentries reflect failed file-name lookups, which are then cached, saving an expensive operation if the file name in question is looked up again. There is no mechanism to proactively prune back those cache entries, however, so the cache keeps growing until memory pressure finally causes the system to forcibly evict some of them, which can make the system unresponsive for a long time or even cause a soft lockup.

One of the memory-management subsystem's most important jobs is reclaiming unused (or little-used) memory so that it can be put to better use. When it comes to one of the core memory-management data structures — page tables — though, this subsystem often falls down on the job. At the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit (LSFMM), David Hildenbrand led a session on the problems posed by the lack of page-table reclaim and explored options for improving the situation.

Greg Kroah-Hartman has announced the release of the 5.17.6, 5.15.38, 5.10.114, and 5.4.192 stable kernels. As usual, these contain important fixes throughout the tree; users of those series should upgrade.

Security updates have been issued by CentOS (firefox and thunderbird), Debian (ecdsautils and libz-mingw-w64), Fedora (cifs-utils, firefox, galera, git, java-1.8.0-openjdk, java-11-openjdk, java-17-openjdk, java-latest-openjdk, mariadb, maven-shared-utils, mingw-freetype, redis, and seamonkey), Mageia (dcraw, firefox, lighttpd, rsyslog, ruby-nokogiri, and thunderbird), Scientific Linux (thunderbird), SUSE (giflib, kernel, and libwmf), and Ubuntu (dbus and rsyslog).

The 5.18-rc6 kernel prepatch is out for testing. "Please do go test it all out - because things may look good now, but continued testing is the only thing that will make sure."

The GCC project has made the first release of the GCC 12 series, GCC 12.1. As the announcement notes, this month is the 35th anniversary of the GCC 1.0 release. There are lots of changes and fixes in this release, including: This release deprecates support for the STABS debugging format and introduces support for the CTF debugging format. The C and C++ frontends continue to advance with extending support for features in the upcoming C2X and C++23 standards and the C++ standard library improves support for the experimental C++20 and C++23 parts. The Fortran frontend now fully supports TS 29113 for interoperability with C.

[...] On the security side GCC can now initialize stack variables implicitly using -ftrivial-auto-var-init to help tracking down and mitigating uninitialized stack variable flaws. The C and C++ frontends now support __builtin_dynamic_object_size compatible with the clang extension. The x86 backend gained mitigations against straight line speculation with -mharden-sls. The experimental Static Analyzer gained uninitialized variable use detection and many other improvements.

There are certain themes that recur regularly at the Linux Storage, Filesystem, Memory-Management, and BPF Summit; among the most reliable is the scalability problems posed by the mmap_lock (formerly mmap_sem) lock. This topic has come up in (at least) 2013, 2018 (twice), and 2019. The 2022 event was no exception, with three consecutive sessions led by Liam Howlett, Michel Lespinasse, and Suren Baghdasaryan dedicated to the topic. There are improvements on the horizon, but the problem is far from solved.

Security updates have been issued by Debian (dpdk, mruby, openjdk-11, and smarty3), Oracle (thunderbird), Red Hat (thunderbird), SUSE (chromium, libvirt, python-Twisted, and tar), and Ubuntu (cron and jbig2dec).

"Hardware poisoning" is a mechanism for detecting and handling memory errors in a running system. When a particular range of memory ceases to remember correctly, it is "poisoned" and further accesses to it will generate errors. The kernel has had support for hardware poisoning for over a decade, but that doesn't mean it can't be improved. At the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit, Yang Shi discussed the challenges of dealing with hardware poisoning when it affects memory used for the page cache.

Security updates have been issued by Debian (firefox-esr), Fedora (firefox, java-1.8.0-openjdk, java-11-openjdk, java-17-openjdk, java-latest-openjdk, recutils, suricata, and zchunk), Oracle (firefox and kernel), Red Hat (firefox), Scientific Linux (firefox), Slackware (mozilla, openssl, and seamonkey), SUSE (apache2-mod_auth_mellon, libvirt, and pgadmin4), and Ubuntu (dpdk, mysql-5.7, networkd-dispatcher, openssl, openssl1.0, sqlite3, and twisted).

The LWN.net Weekly Edition for May 5, 2022 is available.

There is a lot of work going on right now on speeding up Python; Kevin Modzelewski gave a presentation at PyCon 2022 on some of that work. Much of it has implications for Python programmers in terms of how to best take advantage of these optimizations in their code. He gave an overview of some of the projects, the kinds of optimizations being worked on, and provided some benchmarks to give a general idea of how much faster various Python implementations are getting—and which operations are most affected.

The folio project is not yet two years old, but it has already resulted in significant changes to the kernel's memory-management and filesystem layers. While much work has been done, quite a bit remains. In the opening plenary session at the 2022 Linux Storage, Filesystem, Memory-management and BPF Summit, Matthew Wilcox provided an update on the folio transition and led a discussion on the work that remains to be done.

Security updates have been issued by Debian (openjdk-17), Fedora (chromium and suricata), Oracle (mariadb:10.5), SUSE (amazon-ssm-agent, containerd, docker, java-11-openjdk, libcaca, libwmf, pcp, ruby2.5, rubygem-puma, webkit2gtk3, and xen), and Ubuntu (linux-raspi).

Version 100.0 of the Firefox browser has been released. New features include video caption display on various proprietary sites, multiple-language spelling checking, invisible scrollbars, and more.

Python's match statement, which provides a long-sought C-like switch statement—though it is far more than that—has now been part of the language for more than six months. One of the authors of the series of Python Enhancement Proposals (PEPs) that described the feature, Brandt Bucher, came to PyCon 2022 in Salt Lake City, Utah to talk about the feature. He gave an overview of its history, some of its many-faceted abilities, a bit about how it was implemented, and some thoughts on its future, in a presentation on April 29, which was the first day of talks for the conference.

Version 4.7 of the SystemTap tracing system is out. "Enhancements to this release include: a new stap-profile-annotate tool, a new --sign-module module signing option, -d is now implied for processes specified with -c/-x".

Security updates have been issued by Debian (jackson-databind, kernel, openvpn, and twisted), Fedora (xz), Mageia (chromium-browser-stable and curl), Oracle (vim and xmlrpc-c), Red Hat (gzip), Slackware (libxml2), SUSE (git, python39, and subversion), and Ubuntu (libvirt and mysql-5.7, mysql-8.0).

The classic NUMA architecture is built around nodes, each of which contains a set of CPUs and some local memory; all nodes are more-or-less equal. Recently, though, "tiered-memory" NUMA systems have begun to appear; these include CPU-less nodes that contain persistent memory rather than (faster, but more expensive) DRAM. One possible use for that memory is to hold less-frequently-used pages rather than forcing them out to a backing-store device. There is an interesting problem that emerges from this use case, though: how does the kernel manage the movement of pages between faster and slower memory? Several recent patch sets have taken differing approaches to the problem of rebalancing memory on these systems.

Richard Hughes announces the fwupd 1.8.0 release and notes that the associated Linux Vendor Firmware Service has now shipped a minimum of 50 million firmware updates.

Just 7 years ago Christian asked me to “make firmware updates work on Linux” and now we have a thriving client project that respects both your freedom and your privacy, and a thriving ecosystem of hardware vendors who consider Linux users first class citizens. Of course, there are vendors who are not shipping updates for popular hardware, but they’re now in the minority — and every month we have two or three new vendor account requests.