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Aujourd’hui — 28 mai 2024LWN

[$] Filesystems and iomap

Par : jake
28 mai 2024 à 13:56
The iomap block-mapping abstraction is being used by more filesystems, in part because of its support for large folios. But there are some challenges in adopting iomap, which was the topic of a discussion led by Ritesh Harjani in a combined storage and filesystem session at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit. One of the main trouble spots is how to handle metadata, which is not an area that iomap has been aimed at.

[$] Measuring memory fragmentation

Par : corbet
28 mai 2024 à 13:29
In the final session in the memory-management track of the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit, the exhausted group of developers looked one more time at the use of huge pages and the associated problem of memory fragmentation. At its worst, this problem can make huge pages harder (and more expensive) to allocate. Luis Chamberlain, who ran the session, felt that people were worried about this problem, but that there was little data on how severe it truly is.

[$] The state of the memory-management community in 2024

Par : corbet
28 mai 2024 à 13:28
A longstanding tradition in the memory-management track of the Linux Storage, Filesystem, Memory-Management and BPF Summit is a session with maintainer Andrew Morton to discuss the overall state of the community and the development process. The 2024 gathering upheld that tradition toward the end of the final day of the event. It seems that Morton and the assembled developers were all happy with how memory-management work is going, but there is always room for improvement.
Hier — 27 mai 2024LWN

Huston: Calling Time on DNSSEC?

Par : corbet
27 mai 2024 à 21:56
Geoff Huston suggests that it is time to give up on DNSSEC and look for a better way to secure the Internet namespace.

What appears to be very clear (to me at any rate!) is that DNSSEC as we know it today is just not going anywhere. It's too complex, too fragile and just too slow to use for the majority of services and their users. Some value its benefits highly enough that they are prepared to live with its shortcomings, but that's not the case for the overall majority of name holders and for the majority of users, and no amount of passionate exhortations about DNSSEC will change this.

[$] LLVM improvements for BPF verification

Par : daroc
27 mai 2024 à 17:04

Alan Jowett gave a remote presentation at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit about what features could be added to LLVM to make writing BPF programs easier. While there is nothing specific to LLVM about BPF code (and the next session in the track was led by GCC developer José Marchesi about better support for that compiler), LLVM is currently the most common way to turn C code into BPF bytecode. That translation, however, runs into problems when the BPF verifier cannot understand the code LLVM's optimizations produce.

[$] Fleshing out memory descriptors

Par : corbet
27 mai 2024 à 13:39
One of the long-term goals of the folio conversion in the kernel's memory-management subsystem is the replacement of the page structure, which describes a page of physical memory, with an eight-byte "memory descriptor". This change would reduce the overhead of tracking physical memory, increase type safety, and make memory management more flexible. Thus far, though, details on what the memory-descriptor future will look like have been relatively scarce. At the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit, Matthew Wilcox led a discussion to try to fill in the picture somewhat.

Security updates for Monday

Par : jake
27 mai 2024 à 13:35
Security updates have been issued by Debian (apache2, bluez, chromium, fossil, libreoffice, python-pymysql, redmine, and ruby-rack), Fedora (buildah, crosswords, dotnet7.0, glycin-loaders, gnome-tour, helix, helvum, libipuz, loupe, maturin, mingw-libxml2, ntpd-rs, perl-Email-MIME, and a huge list of Rust-based packages due to a "mini-mass-rebuild" that updated the toolchain to Rust 1.78 and picked up fixes for various pieces), Mageia (chromium-browser-stable, mariadb, and roundcubemail), Oracle (kernel, libreoffice, nodejs, and tomcat), and SUSE (cJSON, libfastjson, opera, postgresql15, python3, and qt6-networkauth).

[$] The rest of the 6.10 merge window

Par : corbet
27 mai 2024 à 13:04
Linus Torvalds released 6.10-rc1 and closed the 6.10 merge window on May 26. By that time, 11,534 non-merge changesets had been pulled into the mainline for the next release; nearly 5,000 of those came in after "The first half of the 6.10 merge window" was written. While the latter half of the merge window tends to focus more on fixes, there was also a lot of new functionality that landed during this time.

[$] The next steps for the maple tree

Par : corbet
27 mai 2024 à 12:48
The maple tree data structure was added during the 6.1 development cycle; since then, it has taken its place at the core of the kernel's memory-management subsystem. Unsurprisingly, work on maple trees is not yet done. Maple-tree maintainer Liam Howlett ran a session in the memory-management track of the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit to discuss the current state of the maple tree and which features can be expected next.
À partir d’avant-hierLWN

[$] Two talks on multi-size transparent huge page performance

Par : corbet
25 mai 2024 à 16:38
Using huge pages has been known for years to improve the performance of many workloads. But traditional huge pages, often sized by the CPU at 2MB, can be difficult to allocate and can waste memory due to internal fragmentation. Driven by both the folio transition and hardware improvements, attention to smaller, multi-size transparent huge pages (mTHPs) has been on the rise. In two memory-management-track sessions at the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit, developers discussed the kernel's ability to reliably allocate mTHPs and the performance gains that result.

[$] Atomic writes without tears

Par : jake
24 mai 2024 à 21:33
John Garry and Ted Ts'o led a discussion about supporting atomic writes for buffered I/O, without any torn (or partial) writes to the device, at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit. It is something of a continuation of a discussion at last year's summit. The goal is to help PostgreSQL, which writes its data using 16KB buffered I/O; it currently has to do a lot of extra work to ensure that its data is safe on disk. A promise of non-torn, 16KB buffered writes would allow the database to avoid doing double writes.

[$] Allocator optimizations for transparent huge pages

Par : corbet
24 mai 2024 à 20:42
The original Linux kernel, posted in 1991, ran on a system with a 4KB page size. Over 30 years later, most of us are still running on systems with 4KB pages, even though the amount of installed memory has grown by a few orders of magnitude. It is generally accepted that using large page sizes results in better performance for most applications, but allocating larger pages is often difficult. During a memory-management session at the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit, Yu Zhao presented his ideas on improving the allocation of huge pages in the kernel.

[$] Recent improvements to BPF's struct_ops mechanism

Par : daroc
24 mai 2024 à 19:37

Kui-Feng Lee spoke early in the BPF track at the 2024 Linux Storage, Filesystem, Memory Management, and BPF Summit about some of the recent improvements to BPF. These changes were largely driven by the sched_ext work that David Vernet had covered in the previous talk. Lee focused on changes relevant to struct_ops programs, but several of those changes apply to all BPF programs.

[$] Readying DNF5 for Fedora 41

Par : jzb
24 mai 2024 à 16:51

With the release of Fedora 40 it's time to start looking ahead to what Fedora 41 has in store. One of the largest changes planned for the next release is a switch to DNF5, a C++ rewrite of the DNF package manager. A previous attempt to make the switch, during the Fedora 39 cycle, was called off, and deferred to Fedora 41. The developers have had nearly a year to address compatibility problems and bring DNF5 to a state suitable to replace DNF4. Signs point to a successful switch in the upcoming release, though there may be a few surprises lurking for Fedora users.

[$] Large-folio support for shmem and tmpfs

Par : corbet
24 mai 2024 à 14:02
The kernel contains a pair of related filesystems that, among other things, can be used for shared-memory applications; shmem is an internal mechanism used within the kernel, while the tmpfs filesystem is mounted and accessible from user space. As is the case elsewhere in the kernel, these subsystems would benefit from the addition of large-folio support. During a joint storage, filesystem, and memory-management session at the 2024 Linux Storage, Filesystem, Memory-Management and BPF Summit, Daniel Gomez talked about the work he is doing to add that support.

BitKeeper, Linux, and licensing disputes: How Linus wrote Git in 14 days (Graphite blog)

Par : corbet
24 mai 2024 à 13:34
This Graphite blog post retells the history of the BitKeeper fiasco and the dawn of the Git era.

When we think of history, we often romanticize it as being born of a sudden stroke of inspiration. But the creation of git shows the far harsher reality of invention: a slowly escalating disagreement over a license; the need for a scrappy backup solution to unblock work; and then continued polishing and iteration through years and years, led not by the inventor, but rather a community.

For those who weren't around in those days, a perusal of the LWN coverage from the time might be of interest too, including:

...and a lot more for those who care to search for it.

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