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* Allow resuming per-CPU arena selection via thread.arena With percpu_arena enabled, thread.arena control is one-directional. A thread can be bound to a manually created arena (an index at or above the per-CPU auto range) to route a bounded region of work to a dedicated, long-lived arena, but there is no way back: thread_arena_ctl returns EPERM for any index within the auto range, and arena_choose_impl only re-selects a per-CPU arena for threads whose current arena is already in that range. So once a thread is bound to a manual arena it stays pinned there forever, and its later allocations land there instead of following the CPU. Treat setting thread.arena to an index within the per-CPU range as a request to resume automatic per-CPU selection: hand the thread back to percpu management (rebinding it to the current CPU's arena via percpu_arena_update) and return 0 instead of EPERM. Binding to a manual arena is unchanged. The requested index is advisory; under percpu the thread is governed by its current CPU, so it resumes on the current CPU's arena regardless of the value passed. Add test/unit/percpu_arena_resume covering the manual-arena to resume round trip with allocs & dallocs happening meanwhile, and update test_thread_arena, which asserted the old EPERM. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
jemalloc is a general purpose malloc(3) implementation that emphasizes fragmentation avoidance and scalable concurrency support. jemalloc first came into use as the FreeBSD libc allocator in 2005, and since then it has found its way into numerous applications that rely on its predictable behavior. In 2010 jemalloc development efforts broadened to include developer support features such as heap profiling and extensive monitoring/tuning hooks. Modern jemalloc releases continue to be integrated back into FreeBSD, and therefore versatility remains critical. Ongoing development efforts trend toward making jemalloc among the best allocators for a broad range of demanding applications, and eliminating/mitigating weaknesses that have practical repercussions for real world applications. The COPYING file contains copyright and licensing information. The INSTALL file contains information on how to configure, build, and install jemalloc. The ChangeLog file contains a brief summary of changes for each release. URL: https://jemalloc.net/