jwmalloc: A Verified Memory Allocator for Mobile Devices

Dynamic memory allocators provide memory allocation and release functionality to languages such as C, C++, and Rust. Existing allocators have been primarily optimized for performance and timely memory release. However, emerging mobile workloads also emphasize CPU, energy, and memory usage under soft real-time constraints.

We present jwmalloc, a novel memory allocator built from the ground up to address these mobile-specific challenges. It is based on three key innovations: a uniform slab size with pooling that enables immediate cross-size-class reuse of any emptied slab; the closed sibling tree, a new data structure for efficiently managing fragments; and a two-buffer lifetime tracker that categorizes short- and long-lived objects to guide memory reclamation. For timely response in soft real-time and oversubscription scenarios, all operations are non-blocking. We verified jwmalloc with a bounded model checker under weak memory models. Replacing jemalloc on a flagship smartphone running real-world workloads, jwmalloc reduces whole-system instructions by 10% and cuts allocator-side instruction counts by 3.84x, while lowering CPU power consumption by 5-11%, all at a comparable memory footprint. jwmalloc has been deployed in production on 12 million commercial mobile devices, operating stably for over 30 billion user hours.