A severe performance regression has been identified in the Linux 7.0 development kernel's new SLUB 'sheaves' slab allocator series. The regression causes a ~64% IOPS drop in workloads with persistent cross-CPU alloc/free patterns (from ~36M to ~13M IOPS on ublk null target benchmarks). Red Hat's Ming Lei reported the issue, and SUSE engineer Vlastimil Babka has devised a partial fix allowing sheaf refill when blocking is not allowed. The fix is pending in a pull request and is expected to land before the Linux 7.0-rc3 release on Sunday, with a follow-up patch still needed for memory-less node scenarios.
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