LWN Articles on Linux Kernel (Liberated Thursday)

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Resurrecting fbdev [LWN.net]
The Linux framebuffer device (fbdev) subsystem has long languished in something of a purgatory; it was listed as "orphaned" in the MAINTAINERS file and saw fairly minimal maintenance, mostly driven by developers working elsewhere in the kernel graphics stack. That all changed, in an eye-opening way, on January 17, when Linus Torvalds merged a change to make Helge Deller the new maintainer of the subsystem. But it turns out that the problems in fbdev run deep, at least according to much of the rest of the kernel graphics community. By seeming to take on the maintainer role in order to revert the removal of some buggy features from fbdev, Deller has created something of a controversy.
Part of the concern within the graphics community is the accelerated timeline that these events played out on. Deller posted his intention to take over maintenance of the framebuffer on Friday, January 14, which received an ack from Geert Uytterhoeven later that day. Two days later, before any other responses had come in, Deller sent a pull request to Torvalds to add Deller as the fbdev maintainer, which was promptly picked up. On January 19, Deller posted reversions of two patch sets that removed scrolling acceleration from fbdev. In the meantime, those reversions had already been made in Deller's brand new fbdev Git tree.
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The first half of the 5.17 merge window [LWN.net]
As of this writing, just short of 7,000 non-merge commits have been pulled into the mainline kernel repository for the 5.17 release. The changes pulled thus far bring new features across the kernel; read on for a summary of what has been merged during the first half of the 5.17 merge window.
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Struct slab comes to 5.17 [LWN.net]
The page structure is at the core of the memory-management subsystem. One of these structures exists for every page of physical memory in the system; they are used to track the status of memory as it is used (and reused) during the lifetime of the system. Physical pages can adopt a number of different identities over time; they can hold user-space data, kernel data structures, DMA buffers, and so on. Regardless of how a page is used, struct page is the data structure that tracks its state. These structures are stored in a discontiguous array known as the system memory map.
There are a few problems that have arisen with this arrangement. The page structure was significantly reorganized for 4.18, but the definition of struct page is still a complicated mess of #ifdefs and unions with no mechanisms to ensure that the right fields are used at any given time. The unlucky developer who needs to find more space in this structure will be hard put to understand which bits might be safe to use. Subsystems are normally designed to hide their internal data structures, but struct page is heavily used throughout the kernel, making any memory-management changes more complicated. One possible change — reducing the amount of memory consumed by page structures by getting rid of the need for a structure for every page — is just a distant dream under the current organization.
So there are a lot of good reasons to remove information from struct page and hide what remains within the memory-management subsystem. One of the outcomes from the folio discussions has been a renewed desire to get a handle on struct page, but that is not a job for the faint of heart — or for the impatient. Many steps will be required to reach that goal. The merging of the initial folio patches for 5.16 was one such step; the advent of struct slab in 5.17 is another.
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