Linux 7.3 Preview: Btrfs 5x Speedup, Chinese Engineers Drive Key Optimizations

Release Timeline

The Linux 7.3 merge window closed on August 30 with rc1. Weekly release candidates followed: rc2 on September 6, rc3 on September 13, rc4 on September 20, then rc5 on September 27, rc6 on October 4, and rc7 on October 11. The stable release is projected for October 18, with a possible one-week slip to October 25 if a serious regression requires an rc8. Notably, Ubuntu 26.10 is scheduled for October 15, three days before the upstream stable release, meaning it will likely ship with a rc7 kernel. This reflects Canonical's 2024 strategy of freezing on the latest upstream kernel at release time.

Storage: Btrfs and EXT4 Speedups

Btrfs receives two fixes that each yield roughly a 5x performance improvement: one targets the logging path, the other targets fsync. Direct I/O throughput rises from about half the theoretical peak to over 90%. EXT4 also benefits from a reworked iomap layer: on high-end NVMe, IOPS increase from 1.92 million to 2.19 million per second, and parallel direct I/O writes are now fully enabled. These changes affect both server and desktop workloads, delivering speed that is imperceptible in latency but measurable in benchmarks. Additionally, Btrfs removes free space v1 as the default; free space tree v2 has been the mkfs default since kernel 5.15, and the kernel side now aligns with that. Existing v1 filesystems remain compatible.

Memory: Fixing a Decade-Old Stutter

Engineers from ZTE identified a bug in Kernel Samepage Merging (KSM): under memory pressure, a single lock could stall applications for hundreds of milliseconds. After the fix, the worst-case latency drops from 705 ms to 1.44 ms. This primarily impacts hosts running virtual machines or containers (KVM, Docker), where occasional freezes may have been caused by KSM. Separately, Xiaomi engineers improved the zsmalloc compressed memory allocator, achieving up to 1.83x speedup on Raspberry Pi 4B, benefiting low-cost edge devices.

Scheduling: ByteDance's SMP Restructuring

ByteDance contributed a symmetric multiprocessing (SMP) restructuring of the scheduler. For network-intensive workloads, the worst-case inter-process call latency falls from 17 ms to 1.5 ms, a 90% reduction. For desktop users this means more stable game frame rates and fewer stutters when background tasks compete with foreground tasks; for servers it directly improves tail latency under heavy network load. The sched_ext extensible scheduling framework also sees significant activity — about 20% of non-driver patches in rc2 relate to sched_ext and its self-tests — signaling a move toward programmable scheduling policies via BPF.

Security: Substantial Hardening

NTFS3 receives a thorough hardening pass: a 21-commit, 922-line update fixes slab-out-of-bounds writes, out-of-bounds reads during reparse and objid initialization, an information leak in ntfs_rename(), and an integer overflow in MFT cluster validation. Basic support for NTFS alternate data streams is also added. Users who move NTFS drives between Linux and Windows will benefit directly.

The in-kernel SMB server ksmbd gets multiple use-after-free fixes in tree connection and oplock break notification handling, adds response name length validation, and implements safer session draining on logoff.

The BPF verifier continues to close attack surfaces: it now correctly infers whether registers are NULL after conditional jumps, rejects pseudo-function references to the main program, blocks dangerous direct tail calls from callback frames, marks certain syscall helpers as sleepable, and plugs speculative execution paths that could leak out-of-bounds pointers. Each closed hole removes a potential privilege escalation vector via eBPF.

For operators, the ksmbd and BPF fixes are exactly the type of patches that will be backported to stable branches. The advice is to avoid compiling mainline kernels for production and instead rely on distribution security announcements.

Hardware and Other Changes

Rust support expands to PowerPC (PPC32BE and PPC64LE), joining ARM32, ARM64, LoongArch, RISC-V, and x86_64. The architecture ports are initially marked experimental but have transitioned to maintained after follow-up patches.

Apple Silicon (M1, M2, M3) gains initial USB4 and Thunderbolt support via a 19-patch series from the Asahi Linux community. XDomain and USB3-over-USB4 tunneling work; PCIe, DisplayPort, and suspend are not yet functional. The accompanying Apple PMGR power management driver saves roughly 1 watt in s2idle.

Early support for AMD's next-generation Zen 6 platform lands, along with a large volume of AMD GPU code (about one-third of rc1). Intel hybrid processor optimizations and support for Xe3P and Nova Lake graphics are also included.

Linus Torvalds personally diagnosed and fixed a VRAM offset calculation error in the Intel Xe driver that caused black screens on Battlemage G21. The fix changed a single character: round_up() to round_down(). The debugging effort involved 24 instrumented patches and 18 reboots; the commit message was AI-generated.

How to Safely Test Linux 7.3

The least recommended approach is installing a mainline kernel on a production machine. Two safer paths:

Use Ubuntu 26.10 Beta or daily images (Beta available since September 24). Install on a spare machine or VM; after October 15 the upgrade to the final release is seamless.

Wait for your distribution to ship the update. Ubuntu 26.10 will include 7.3 on October 15; Ubuntu 26.04 LTS users will receive it via the HWE kernel on a slower cadence, which is appropriate for stability.

Regardless of the path, create a Timeshift snapshot before upgrading and never test on your only working machine.

Relevance to Your Use Case

Desktop daily use: Perceptible impact is low, but older machines see more stable frame rates.

Servers and storage workloads: Direct benefits from Btrfs and EXT4 performance improvements.

Container and VM hosts: KSM fix eliminates mysterious freezes.

NTFS data exchange: NTFS3 security hardening directly relevant.

ksmbd or BPF users: A batch of fixes will be backported; track stable updates.

Raspberry Pi and edge devices: zsmalloc speedup makes small machines smoother.

The author judges this release worth waiting for: it combines performance-oriented changes with concrete security hardening, and LTS maintainers typically cherry-pick patches from such versions for long-term maintenance.