Kernel 6.19 integrates RSEQ-based fix for TCMalloc performance regression

The Linux kernel 6.19 introduces a fix for a TCMalloc performance regression by leveraging restartable sequences (RSEQ). RSEQ is a kernel feature that allows user-space applications to perform lockless operations while detecting preemption events. If preemption occurs during an RSEQ operation, the kernel signals the application to restart the operation, avoiding race conditions without traditional locking overhead.

This fix targets applications using TCMalloc, a memory allocator optimized for low-latency and high-throughput scenarios. The regression likely stemmed from inefficiencies in handling preemption during critical memory operations, which RSEQ mitigates by ensuring atomicity without explicit locks. However, the fix requires both kernel support (version 6.19 or later) and user-space integration, meaning applications must explicitly adopt RSEQ-aware code paths.

For engineers, the change reduces latency spikes in TCMalloc-dependent workloads but introduces a dependency on kernel features. Applications running on older kernels or without RSEQ support will not benefit from the fix. Additionally, RSEQ operations are limited to simple, bounded sequences, so complex memory operations may still require traditional synchronization mechanisms. The fix is most relevant for performance-critical systems where TCMalloc is already in use.