RHmalloc : a very large, highly concurrent dynamic memory manager
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Dynamic memory management (DMM) is a fundamental aspect of computing, directly affecting the capability, performance and reliability of virtually every system in existence today. Yet oddly, the fifty year research into DMM has not taken memory capacity into account, having fallen significantly behind hardware trends. Comparatively little research work on scalable DMM has been conducted – of the order of ten papers exist on this topic – all of which focus on CPU scalability only; the largest heap reported in the literature to date is 600MB. By contrast, symmetric multiprocessor (SMP) machines with terabytes of memory are now commercially available. The contribution of our research is the formal exploration, design, construction and proof of a general purpose, high performance dynamic memory manager which scales indefinitely with respect to both CPU and memory – one that can predictably manage a heap of arbitrary size, on any SMP machine with an arbitrary number of CPU’s, without a priori knowledge. We begin by recognizing the scattered, inconsistency of the literature surrounding this topic. Firstly, to ensure clarity, we present a simplified introduction, followed by a catalog of the fundamental techniques. We discuss the melting pot of engineering tradeoffs, so as to establish a sound basis to tackle the issue at hand – large scale DMM. We review both the history and state of the art, from which significant insight into this topic is to be found. We then explore the problem space and suggest a workable solution. Our proposal, known as RHmalloc, is based on the novel perspective that, a highly scalable heap can be viewed as, an unbounded set of finite-sized sub-heaps, where each sub-heap maybe concurrently shared by any number of threads; such that a suitable sub-heap can be found in O(1) time, and an allocation from a suitable sub-heap is also O(1). Testing the design properties of RHmalloc, we show by extrapolation that, RHmalloc will scale to at least 1,024 CPU’s and 1PB; and we theoretically prove that DMM scales indefinitely with respect to both CPU and memory. Most importantly, the approach for the scalability proof alludes to a general analysis and design technique for systems of this nature.
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