A study of memory management for web-based applications on multicore processors

Abstract

More and more server workloads are becoming Web-based. In these Web-based workloads, most of the memory objects are used only during one transaction. We study the effect of the memory management approaches on the performance of such Web-based applications on two modern multicore processors. In particular, using six PHP applications, we compare a general-purpose allocator (the default allocator of the PHP runtime) and a region-based allocator, which can reduce the cost of memory management by not supporting per-object free. The region-based allocator achieves better performance for all workloads on one processor core due to its smaller memory management cost. However, when using eight cores, the region-based allocator suffers from hidden costs of increased bus traffics and the performance is reduced for many workloads by as much as 27.2% compared to the default allocator. This is because the memory bandwidth tends to become a bottleneck in systems with multicore processors. We propose a new memory management approach, defrag-dodging , to maximize the performance of the Web-based workloads on multicore processors. In our approach, we reduce the memory management cost by avoiding defragmentation overhead in the malloc and free functions during a transaction. We found that the transactions in Web-based applications are short enough to ignore heap fragmentation, and hence the costs of the defrag-mentation activities in existing general-purpose allocators outweigh their benefits. By comparing our approach against the region-based approach, we show that a per-object free capability can reduce bus traffic and achieve higher performance on multicore processors. We demonstrate that our defrag-dodging approach improves the performance of all the evaluated applications on both processors by up to 11.4% and 51.5% over the default allocator and the region-based allocator, respectively.

ABT and SBT Revisited: Efficient Memory Management Techniques for Object Oriented and Web-based Applications

“…This is the case for web-based applications where memory objects belong to transactions. Inoue et al have shown that allocators which tend to perform coalescing on each case of freeing an object behave poorly in multicore environments [18]. The allocation technique that they suggested eliminates coalescing, which in turn reduces bus tra c in multicore processors; it makes 11.4% to 51.5% performance improvement compared to default allocators which do perform coalescing [18].…”