Implementation of a constant‐time dynamic storage allocator

Abstract

This paper describes the design criteria and implementation details of a dynamic storage allocator for real-time systems. The main requirements that have to be considered when designing a new allocator are concerned with temporal and spatial constraints. The proposed algorithm, called TLSF (two-level segregated fit), has an asymptotic constant cost, O(1), maintaining a fast response time (less than 200 processor instructions on a x86 processor) and a low level of memory usage (low fragmentation). TLSF uses two levels of segregated lists to arrange free memory blocks and an incomplete search policy. This policy is implemented with word-size bitmaps and logical processor instructions. Therefore, TLSF can be categorized as a good-fit allocator. The incomplete search policy is shown also to be a good policy in terms of fragmentation. The fragmentation caused by TLSF is slightly smaller (better) than that caused by best fit (which is one of the best allocators regarding memory fragmentation). In order to evaluate the proposed allocator, three analyses are presented in this paper. The first one is based on worst-case scenarios. The second one provides a detailed consideration of the execution cost of the internal operations of the allocator and its fragmentation. The third analysis is a comparison with other well-known allocators from the temporal (number of cycles and processor instructions) and spatial (fragmentation) points of view. In order to compare them, a task model has been presented.

Fast Bitmap Fit: A CPU Cache Line friendly memory allocator for single object allocations

“…The implementation relies on specific processor instructions related to bit manipulation, and the run-time cost is linear in the worst case. There have been more efficient variants proposed [8], but these remain fairly complex in terms of implementation complexity.…”

A switchable approach to large object allocation in real-time Java

“…More information on memory allocators can be found in Wilson et al's survey [28]. A review of the most well-known allocators can also be found in [27]. This paper focuses on contiguous allocation and presents a switchable approach to large object allocation, partially based on Boyer and Moore's string search algorithm.…”

“…As this study is about large object allocation we will not cover the details of defragmentation support of Ovm. On the other hand, for efficient memory allocation, one can prefer to use state-of-the-art allocators like binary-buddy [22][23][24], half-fit [25], Masmano et al's TLSF [26,27], or Doug Lea's (a memory allocator, Unix/Mail 1996) allocators. More information on memory allocators can be found in Wilson et al's survey [28].…”

“…More information on memory allocators can be found in Wilson et al's survey [28]. A review of the most well-known allocators can also be found in [27].…”