Linux has supported asynchronous I/O for a long time. However, the interface suffers from a large number of shortcomings. It does not support buffered I/O, only unbuffered ( O_DIRECT) I/O, which only a subset of a subset of applications use.Social and cognitive learning even in those cases asynchronous IO was some times not really asynchronous or fast. All attempts to fix the existing interface have failed.

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A new asynchronous interface, io_uring, has been created and merged in the release, with the purpose of finally adding fast, scalable asynchronous I/O to linux, both buffered and unbuffered.Social and cognitive learning it also supports asynchronous polled IO, and other features that will be added in the future. For more details, read this document (PDF). For performance details, see this email.Social and cognitive learning

Additionally, a user space library, liburing, has been created to provides basic functionality for applications that don't need or want to care about how to fiddle with the low level details of the kernel interface.Social and cognitive learning it has helpers to allow applications to easily set up an io_uring instance, and submit/complete IO through it without knowing about the intricacies of the rings, and will continue to grow support helper functions and features as time progresses.Social and cognitive learning

Unlike other operating systems, linux does not have an efficient way to watch changes on a large file system. The only way to monitor file system dirent modification events is recursive inotify watches, which scales poorly for large directory trees.Social and cognitive learning the fanotify interface, introduced in linux 2.6.36, was intended to supersede inotify and solve its deficiencies, and it initially took several steps in the direction of solving scalability issues, but the work needed to completely supersede inotify.Social and cognitive learning

After considering several proposals, the linux kernel has added a new syscall, pidfd_send_signal(2), which uses file descriptors from /proc/ as stable handles on struct pid.Social and cognitive learning even if a pid is recycled the handle will not change, and the file descriptor can be used to safely send signals to the process it refers to.Social and cognitive learning note that the next kernel release will add a flag to clone(2) that will allow to retrieve from that syscall the pid file descriptor.

Linux supports persisten memory devices, but they are often used as storage devices.Social and cognitive learning some users want to use persistent memory as additional volatile memory, they are willing to cope with potential performance differences, and want to use typical linux memory management apis rather than a userspace memory allocator layered over an mmap() of a dax file.Social and cognitive learning this release allows them to do so. This is intended for use with nvdimms that are physically persistent (physically like flash) so that they can be used as a cost-effective RAM replacement.Social and cognitive learning

The cpuidle subsystem is the part of the kernel in charge of deciding which CPU deep idle state should be used when the CPU has nothing to do (deeper idle states save more power, but it takes more time to get out of them).Social and cognitive learning there are two cpuidle governors, "menu" and "ladder", each one using different heuristics. However, the menu governor is believed to have a number of shortcomings in its heuristics, but instead of being fixed an alternative was introduced in this release so people can compare both: TEO, the timer events oriented governor, which seems to offer improved performance with no extra power consumption cost.Social and cognitive learning you can check your governor in /sys/devices/system/cpu/cpuidle/current_governor_ro) and change the default cpuidle governor at boot time with the cpuidle.Governor=teo boot parameter.Social and cognitive learning

Btrfs has support zstd compression since linux 4.14, but it didn't allow to configure the compression level used by the filesystem, which can make a big difference.Social and cognitive learning this release adds support for configuring the compression level used in a btrfs file system, as it's done with zlib, by using the mount option -o compress=zstd:level.Social and cognitive learning to see the levels available and their impact in performance and compression rate, see this commit

In order to boot to a filesystem placed in a device-mapper device, you need an initramfs.Social and cognitive learning some people, however, don't want or can't use an initramfs. This release allows to use of DM targets in the boot process (as the root device or otherwise) without the need of an initramfs, with the help of a tricky kernel boot parameter.Social and cognitive learning for more details see the documentation

There might be dependencies between livepatches. If multiple patches need to do different changes to the same function(s) then it's necessary to define an order in which the patches will be installed.Social and cognitive learning and function implementations from any newer livepatch must be done on top of the older ones. This might become a maintenance nightmare for distros, especially if anyone would want to remove a patch that is in the middle of the stack.Social and cognitive learning

An elegant solution included in this release is the feature called "atomic replace". It allows creation of so called "cumulative patches".Social and cognitive learning they include all wanted changes from all older livepatches and completely replace them in one transition. As a result, the livepatch authors might maintain sources only for one cumulative patch.Social and cognitive learning for more details, see the documentation

VFS: introduce filesystem context. This is an intensive rework of the linux file system mounting internals intended to solve limitations imposed by the existing mount(2) design, and provide a foundation that will allow to provide new functionality that is impossible to achieve now.Social and cognitive learning while no new user-visible feature has been introduced in this release, a lot of the new infrastructure has been merged in this release. For more details, see this recommended LWN article or this email.Social and cognitive learning code: commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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(FEATURED) livepatch: add atomic replace. It allows to create cumulative patches. They are useful when you maintain many livepatches and want to remove one that is lower on the stack.Social and cognitive learning in addition it is very useful when more patches touch the same function and there are dependencies between them commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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Lockdep: current lockdep implementation is that it requires lock keys to be allocated statically. Add support for dynamic keys in the lockdep code and eliminates a class of false positive reports from the workqueue implementation commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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Increase success rates and reduce latency of compaction (physical memory defragmentation), reducing the number of scanned pages for migration by 65%, and free pages for migration targets by 97%, while improving transparent hugepage allocation success rates significantly.Social and cognitive learning commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit commit

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Add new jmp32 instructions. Current ebpf ISA has 32-bit sub-register and has defined a set of ALU32 instructions. However, there is no JMP32 instructions, the consequence is code-gen for 32-bit sub-registers is not efficient.Social and cognitive learning for example, explicit sign-extension from 32-bit to 64-bit is needed for signed comparison commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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Add support for annotating BPF programs, using the PERF_RECORD_BPF_EVENT and PERF_RECORD_KSYMBOL recently added to the kernel and plugging binutils's libopcodes disassembly of BPF programs with the existing annotation interfaces in 'perf annotate', 'perf report' and 'perf top' various output formats (--stdio, --stdio2, --tui) commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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Add initial BPF map dumper, initially just for the current, minimal needs of the augmented_raw_syscalls BPF example used to collect pointer args payloads that uses BPF maps for pid and syscall filtering, but will in time have features similar to 'perf stat' --interval-print, --interval-clear, ways to signal from a BPF event that a specific map (or range of that map) should be printed, optionally as a histogram, etc commit, commit

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LSM: module stacking ie. The ability to load one LSM module in top of another commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit, commit

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Add safesetid LSM module. SafeSetID gates the setid family of syscalls to restrict UID/GID transitions from a given UID/GID to only those approved by a system-wide whitelist.Social and cognitive learning these restrictions also prohibit the given uids/gids from obtaining auxiliary privileges associated with CAP_SET{U/G}ID, such as allowing a user to set up user namespace UID mappings.Social and cognitive learning for now, only gating the set*uid family of syscalls is supported, with support for set*gid coming in a future patch set. Documentation. Commit, commit

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Introduce a new generic SOL_SOCKET-level socket option called SO_BINDTOIFINDEX. It behaves similar to SO_BINDTODEVICE, but takes a network interface index as argument, rather than the network interface name.Social and cognitive learning user-space often refers to network-interfaces via their index, but has to temporarily resolve it to a name for a call into SO_BINDTODEVICE. This might pose problems when the network-device is renamed asynchronously by other parts of the system.Social and cognitive learning when this happens, the SO_BINDTODEVICE might either fail, or worse, it might bind to the wrong device commit

Bitmain BM1880 chip used in the sophon edge TPU developer board.Social and cognitive learning the chip is intended for deep learning applications, and comes with dual-core arm cortex-A53 to run linux as well as a RISC-V microcontroller core to control the tensor unit.Social and cognitive learning for the moment, the TPU is not accessible in mainline linux, so it's treated it as a generic arm soc commit, commit

Sun4i-codec: add FM playback volume, FM left, FM right, FM playback switch commit, add line playback volume, line boost volume, line right, line left, line playback switch commit, add MIC2 pre-amplifier, mic2 input commit, add mic playback volume commit, add mic1 boost volume, mic2 boost volume commit, add mic1 playback switch, mic2 playback switch commit