SLUB Adapted To Be Real-Time Linux Compatible (PREEMPT_RT)
The big RT addition for Linux 5.15 was the PREEMPT_RT locking code being merged and that representing a bulk of the previously outstanding real-time patches needing to be upstreamed. That is a big milestone albeit not across the finish line yet and more of the kernel code continues to be adapted to make it compatible with RT configurations.
Linux's SLUB memory management code on Wednesday saw RT support merged. The SLUB allocation code is now considered "fully PREEMPT_RT compatible" and so far has been found to not introduce any performance regressions for RT or non-RT kernel configurations -- besides the expected RT tradeoff of some throughput regressions due to preemption improvements through the RT mutex.
The merge comment notes, "This series was initially inspired by Mel's pcplist local_lock rewrite, and also interest to better understand SLUB's locking and the new primitives and RT variants and implications. It makes SLUB compatible with PREEMPT_RT and generally more preemption-friendly, apparently without significant regressions, as the fast paths are not affected."
More details on the SLUB changes for Linux 5.15 via the merge.