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In a plenary session on the first day of the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit, Stephen Bates led a discussion about peer-to-peer DMA (P2PDMA). The idea is to remove the host system's participation in a transfer of data from one PCIe-connected device to another. The feature was originally aimed at NVMe SSDs so that data could simply be copied directly to and from the storage device without needing to move it to system memory and then from there to somewhere else.

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DAMON is a framework that allows user space to influence and control the kernel's memory-management operations. It first entered the kernel with the 5.15 release, and has been gaining capabilities ever since. At the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit, DAMON author Seongjae Park provided an overview of the current status of DAMON development and where it can be expected to go in the near future.

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In a remotely presented, memory-management-track session at the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit, Frank van der Linden pointed out that the line dividing resources controlled by the kernel from those managed by user space has moved back and forth over the years. He is currently interested in making it possible for user space to take more control over the management of memory resources. A proposal was discussed in general terms, but it will require some real scrutiny on its way toward the mainline, if it ever gets there.

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Overcommitting memory is a longstanding tradition in the Linux world (and beyond); it is rare that an application uses all of the memory allocated to it, so overcommitting can help to improve overall memory utilization. In situations where memory has been overcommitted, though, it may be necessary to respond quickly to ensure that applications have the memory they actually need, even when those needs change. At the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit, T.J. Alumbaugh (in the room) and Yuanchu Xie (remotely) presented a new mechanism intended to help hosts provide containerized guests with the memory resources they need.

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Virtual-machine hosting can be a fickle business; once a virtual machine has been placed on a physical host, there may arise a desire to move it to a different host. The problem with migrating virtual machines, though, is that there is a period during which the machine is not running; that can be disruptive even if it is brief. At the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit, Dragan Stancevic, presenting remotely, showed how CXL shared memory can be used to migrate virtual machines with no offline time.

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The Linux CPU scheduler will let realtime tasks hog the CPU to the exclusion of everything else — except when it doesn't. At the 2023 Open Source Summit North America, Joel Fernandes covered the problems with the kernel's realtime throttling mechanism and a couple of potential solutions. As a bonus, since the room was unscheduled for the following slot, attendees were treated to a spontaneous session on adaptive spinning in user space run by André Almeida.

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Memory tiering is the practice of dividing physical memory into separate levels according to its performance characteristics, then allocating that memory in a (hopefully) optimal manner for the workload the system is running. The subject came up repeatedly during the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit. One session, led by David Rientjes, focused directly on tiering and how it might be better supported by the Linux kernel.

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Kyungsan Kim began his talk at the 2023 Linux Storage, Filesystem, Memory-Management and BPF Summit with a claim that the Compute Express Link (CXL) technology is leading to fundamental changes in computer architecture. The kernel will have to respond with changes of its own, including in its memory-management layer. Drawing on some experience gained at Samsung, Kim had a few suggestions on the form those changes should take — suggestions that ran into some disagreement from other memory-management developers.

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In part one of the tale, Brandt Bucher looked specifically at the CPython optimizations that went into Python 3.11 as part of the Faster CPython project. More of that work will be appearing in future Python versions, but on day two of PyCon 2023 in Salt Lake City, Utah, Mark Shannon provided an overall picture of CPython optimizations, including efforts made over the last decade or more, with an eye toward the other areas that have been optimized, such as the memory layout for the internal C data structures of the interpreter. He also described some additional optimization techniques that will be used in Python 3.12 and beyond.

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Mike Rapoport has put a considerable amount of effort into solving the problem of direct-map fragmentation over the years; this has resulted in proposals like __GFP_UNMAPPED and a session at the 2022 Linux Storage, Filesystem, Memory-Management, and BPF Summit. Rapoport returned at the 2023 Summit to revisit this issue, but he started with a somewhat surprising spoiler.

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