All posts by corbet

[$] Swap tables, flash-friendly swap, swap_ops, and more

Post Syndicated from corbet original https://lwn.net/Articles/1072657/

The kernel’s swap subsystem is charged with managing anonymous pages in
secondary storage when those pages are (hopefully) not being used and the
memory they occupy is needed elsewhere. This long-unloved subsystem has
seen a resurgence of developer interest in recent times, so it is not
surprising that it was the topic of three separate sessions in the
memory-management track at the
2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit. Two of those sessions
were concerned with improving the performance and maintainability of the
swap code, while one (shared with the storage track) was about how swapping
could be friendlier to solid-state storage devices.

Security updates for Monday

Post Syndicated from corbet original https://lwn.net/Articles/1073356/

Security updates have been issued by AlmaLinux (freerdp, gimp:2.8, jq, kernel, and rsync), Debian (chromium, ffmpeg, firewalld, kernel, nginx, openjpeg2, openssh, php7.4, and redis), Fedora (apptainer, chromium, coturn, dnsmasq, firefox, kernel, libgit2_1.8, libmetal, nginx, nginx-mod-brotli, nginx-mod-fancyindex, nginx-mod-headers-more, nginx-mod-js-challenge, nginx-mod-modsecurity, nginx-mod-naxsi, nginx-mod-vts, open-amp, perl-Net-CIDR-Lite, pgbouncer, pypy, python-jupytext, python-uv-build, rsync, rust-astral-tokio-tar, uriparser, uv, valkey, and yelp), Mageia (dpkg, firefox, thunderbird, golang, haproxy, and samba), Slackware (dnsmasq and kernel), and SUSE (apache-commons-configuration2, apache2, apptainer, chromedriver, cups-filters, curl, dnsmasq, expat, ffmpeg-4, ffmpeg-7, firebird, firewalld, flux2-cli, glibc, go1.25, go1.26, gosec, grub2, ImageMagick, java-11-openj9, java-17-openj9, java-1_8_0-openj9, java-1_8_0-openjdk, java-21-openj9, java-25-openj9, kdenlive, kernel, kernel-devel, keylime-config, krb5, libIex-3_4-33, mozjs115, mozjs78, nginx, openssh, openvswitch, ovmf, PackageKit, perl-Crypt-URandom, perl-CryptX, perl-libwww-perl, perl-Net-CIDR-Lite, perl-Text-CSV_XS, podman, postgresql17, postgresql18, python-pyOpenSSL, python310, rsync, sed, tekton-cli, valkey, xen, and zypper-docker).

Kernel prepatch 7.1-rc4

Post Syndicated from corbet original https://lwn.net/Articles/1073193/

The 7.1-rc4 kernel prepatch is out for
testing.

Some of the documentation updates might be worth highlighting: the
continued flood of AI reports has basically made the security list
almost entirely unmanageable, with enormous duplication due to
different people finding the same things with the same
tools. People spend all their time just forwarding things to the
right people or saying “that was already fixed a week/month ago”
and pointing to the public discussion.

Which is all entirely pointless churn, and we’re making it clear
that AI detected bugs are pretty much by definition not secret, and
treating them on some private list is a waste of time for everybody
involved – and only makes that duplication worse because the
reporters can’t even see each other’s reports.

(He is referring to this
pull request with patches from Willy Tarreau defining what constitutes a security
bug and responsible
ways to use AI to find bugs).

[$] Controlling memory-management with BPF

Post Syndicated from corbet original https://lwn.net/Articles/1072538/

Roman Gushchin began his session in the memory-management track of the
2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit by saying that the
community has seen a lot of proposals adding BPF-based interfaces for
memory management. None of them have made their way into the mainline,
though. He wanted to explore the ways in which BPF might be helpful and
the obstacles that have kept BPF-based solutions out so far. This session
was followed by a discussion led by Shakeel Butt on what the requirements
for a new, BPF-based interface for memory control groups might look like.

[$] HugeTLB preservation over live update

Post Syndicated from corbet original https://lwn.net/Articles/1072531/

Recent times have seen a lot of effort put into the implementation of the kexec handover and live update orchestrator
features in the Linux kernel. But that work is not yet complete. At the
2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, Pratyush Yadav led a
memory-management-track session on adding the ability to preserve hugetlbfs-provided
memory during the live-update process.

[$] Policy groups for memory management

Post Syndicated from corbet original https://lwn.net/Articles/1072517/

The kernel’s control-group
subsystem works well for resource management, Chris Li said at the
beginning of his memory-management-track session at the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit. Control groups work
less well for other use cases, though. He was there to present his
proposed enhancement, called “policy groups”, that would address some of
the shortcomings that he has encountered. A consensus on how this feature
should look still seems distant, though.

[$] Keeping COWs in context (a.k.a. anonymous reverse mapping)

Post Syndicated from corbet original https://lwn.net/Articles/1072378/

The kernel’s reverse-mapping machinery is charged with locating the
page-table entries that refer to a given page in memory. The reverse
mapping of anonymous pages is handled differently than for file-backed
pages. The kernel’s implementation of reverse mapping for anonymous pages
is, according to Lorenzo Stoakes in his proposal
for a memory-management-track session at the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, “a very broken
abstraction“, due to its complexity. It also has some performance
problems. Stoakes was there to present, in raw form, a proposed
replacement that he calls a “COW context”.

[$] LWN.net Weekly Edition for May 14, 2026

Post Syndicated from corbet original https://lwn.net/Articles/1071535/

Inside this week’s LWN.net Weekly Edition:

  • Front: Fedora AI; Forgejo "carrot" disclosure; memory-management maintainership; huge THPs; mshare; 64KB base pages; DAMON; direct map.
  • Briefs: Dirty Frag; Fragnesia; Mythos and curl; killswitch; Debian reproducible builds; KDE investment; Quotes …
  • Announcements: Newsletters, conferences, security updates, patches, and more.

[$] Managing pages outside of the direct map

Post Syndicated from corbet original https://lwn.net/Articles/1072367/

When Brendan Jackman proposed
a session for the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, his topic was “a
pagetable library for the kernel“. During the actual
memory-management-track session, though, he stated that the idea had
“fizzled” and he was going to cover related topics instead. What
resulted was a session on ways to efficiently manage pages that are not
present in the kernel’s direct map.

[$] Revisiting mshare

Post Syndicated from corbet original https://lwn.net/Articles/1072333/

Linux can share memory between processes, but each process (almost always)
has its own set of page tables. In situations where vast numbers of
processes are sharing a memory region, the combined size of the page
tables can exceed that of the shared memory itself. There has, thus, long
been an interest in enabling unrelated processes to share page tables
referring to shared memory. Anthony Yznaga is the latest developer to try
to push this idea (known as “mshare”) forward; he described the status of
that work in a memory-management-track discussion at the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit (LSFMM+BPF).

[$] Using dma-bufs for read and write operations

Post Syndicated from corbet original https://lwn.net/Articles/1072317/

The kernel’s dma-buf
subsystem provides a way for drivers to share memory buffers, usually
in order to support efficient device-to-device I/O. At the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, Pavel Begunkov, assisted
by Kanchan Joshi, led a joint session of the storage and memory-management
tracks to explore ways to make the use of dma-bufs more efficient yet, and
to make them available for read and write operations initiated by user
space.

[$] Scaling transparent huge pages to 1GB

Post Syndicated from corbet original https://lwn.net/Articles/1071716/

As a general rule, when developers talk about huge pages, they are
referring to PMD-level pages that are 1MB or 2MB in size, depending on the
CPU architecture. Most CPUs can support other huge-page sizes, though. On
x86 systems, PUD-level huge pages hold 1GB of data. Providing such large
pages transparently to processes has generally not been considered as
either feasible or desirable, but Usama Arif is trying to change that
assessment. At the 2026 Linux Storage,
Filesystem, Memory Management, and BPF Summit, he led a session in the
memory-management track on how to make transparent huge pages (THPs) truly
huge.

[$] Providing 64KB base pages with 4KB kernels, two different ways

Post Syndicated from corbet original https://lwn.net/Articles/1071484/

Some CPU architectures are able to run with a number of different base-page
sizes; using a larger size can often result in better performance at the
cost of increased memory use. Other architectures are more limited. At
the 2026 Linux
Storage, Filesystem, Memory Management, and BPF Summit, two sessions in
the memory-management track explored options for letting processes run with
64KB page sizes when the underlying kernel does not. The first was focused
on letting each process have its own page size, while the second concerned
bringing 64KB pages to x86 systems.

Debian to require reproducible builds

Post Syndicated from corbet original https://lwn.net/Articles/1072314/

Paul Gevers has slipped an interesting bit of news into a “bits from the release
team” message:

Aided by the efforts of the Reproducible Builds project, we’ve
decided it’s time to say that Debian must ship reproducible
packages. Since yesterday, we have enabled our migration software
to block migration of new packages that can’t be reproduced or
existing packages (in testing) that regress in reproducibility.

As Gioele Barabucci pointed
out, “reproducible” in this sense is limited to building within an
instance of Debian’s build environment, which is a tighter requirement than
is normally used. It is still a big step forward for reproducible builds.

killswitch for short-term emergency vulnerability mitigation

Post Syndicated from corbet original https://lwn.net/Articles/1071861/

It seems that we are in for an extended period of the disclosure of
vulnerabilities before fixes become available. One possible way of coping
with this flood might be the killswitch
proposal from Sasha Levin. In short, killswitch can immediately disable
access to specific functionality in a running kernel, essentially blasting
a vulnerable path (and its associated functionality) out of existence until
a fix can be installed. “For most users, the cost of ‘this socket
family stops working for the day’ is much smaller than the cost of running
a known vulnerable kernel until the fix land.“

[$] A 2026 DAMON update

Post Syndicated from corbet original https://lwn.net/Articles/1071256/

The kernel’s DAMON subsystem
provides user-space monitoring and management of system memory. DAMON is
developing rapidly, so an update on its progress has become a regular
feature of the annual Linux Storage,
Filesystem, Memory Management, and BPF Summit. This tradition
continued at the 2026 gathering with an update from DAMON creator SeongJae
Park covering a long list of new capabilities — tiering, data attributes
monitoring, transparent huge pages, and more — being added to this subsystem.