Swap Device Research Articles

Rectifying Skewed Kernel Page Reclamation in Mobile Devices for Improving User-Perceivable Latency

A crucial design factor for users of smart mobile devices is the latency of graphical interface interaction. Switching a background app to foreground is a frequent operation on mobile devices and the latency of this process is highly perceivable to users. Based on an Android smartphone, through analysis of memory reference generated during the app-switching process, we observe that file (virtual) pages and anonymous pages are both heavily involved. However, to our surprise, the amounts of the two types of pages in the main memory are highly imbalanced, and frequent I/O operations on file pages noticeably slows down the app-switching process. In this study, we advocate to improve the app-switching latency by rectifying the skewed kernel page reclaiming. Our approach involves two parts: proactive identification of unused anonymous pages and adaptive balance between file pages and anonymous pages. As mobile apps are found inflating their anonymous pages, we propose identifying unused anonymous pages in sync with the app-switching events. In addition, Android devices replaces the swap device with RAM-based zram, and swapping on zram is much faster than file accessing on flash storage. Without causing thrashing, we propose swapping out as many anonymous pages to zram as possible for caching more file pages. We conduct experiments on a Google Pixel phone with realistic user workloads, and results confirm that our method is adaptive to different memory requirements and greatly improves the app-switching latency by up to 43% compared with the original kernel.

Feasibility analysis of using a bubble column evaporator as a solvent swap device

A feasibility analysis was performed on the use of a bubble column evaporator (BCE) as a solvent swap device. Batch BCE simulations successfully proved that the BCE was capable of performing a solvent swap for both the dcm - methanol and the water - methanol systems with the aid of computational fluid dynamics (CFD). This was achieved by saturating the inlet gas with the new solvent which condensed inside the column. The old solvent then evaporated into the gas phase which exited via the column outlet. Progression of the solvent swap therefore caused the liquid mass fraction of the species to vary. The effect of bubble size, gas flowrate, gas inlet temperature and liquid mass fraction on the solvent swap efficiency was also investigated. The liquid mass fraction was found to have the greatest influence on the solvent swap efficiency. The evaporation rate decreased proportionately with the mass fraction of the evaporating species in the liquid phase which was a result of Raoult’s law. The thermodynamic model was used to validate the CFD solution and estimate the time required for a batch solvent swap. A smaller bubble size was found to enhance mass transfer in the solvent swap by increasing the evaporation and condensation thermodynamic efficiencies. The higher gas flowrate also improved the mass transfer in the system and reduced the time required for a solvent swap as there was a greater throughput of gas, however it resulted in a decreased evaporation efficiency due to a lower gas residence time in the column. The higher gas inlet temperature increased the rate of condensation and the time required for the a solvent swap. The increased condensation of the new solvent had a negative effect on the evaporation of the old solvent as a result of raoults law which resulted in a longer solvent swap operation. The increased gas inlet temperature also caused the evaporation rate to decrease because of the relationship between the density of an ideal gas and temperature. An increased inlet gas temperature resulted in a lower inlet gas density. There was therefore a reduced mass throughput of gas into the column and consequentially the rate of evaporation decreased. The liquid mass fraction was found to have the greatest influence on the solvent swap efficiency. The evaporation rate decreased proportionately with the mass fraction of the evaporating species in the liquid phase which was a result of Raoult’s law.

Numerical optimisation of a ship wind-assisted propulsion system using blowing and suction over a range of wind conditions

A Kriging surrogate model and a genetic algorithm are used to optimise the geometry of a ship wind assisted propulsion system (SWAP). The SWAP device is an actively controlled aerofoil mounted vertically on the deck of a ship in order to produce a forward propulsive force from the wind. The SWAP concept uses a circulation control system which employs both blowing from the leading edge and suction from the trailing edge. The aerodynamic parameters of the sail are found using a computational fluid dynamics (CFD) model validated against experimental data for a similar system, the coflow jet aerofoil. Further application of Kriging models is used to predict maximum lift coefficients for multiple freestream velocities, ensuring that the optimised device offers robust performance and low sensitivity to expected variations in wind speed. The maximum achievable lift coefficient was found to be 13.17% greater than for the baseline aerofoil over a range of wind speeds from 8–12 m/s.

A Remote Memory Sharing System for Virtualized Computing Infrastructures

Resource management is a critical issue in today’s virtualized computing infrastructures. Consolidation is the main technique used to optimize such infrastructure. Regarding memory management, it allows gathering overloaded and underloaded VM on the same server so that memory can be mutualized. However, because of infrastructures constraints and complexity of managing multiple resources, consolidation can hardly optimize memory management. In this article, we propose to rely on a remote memory sharing for mutualizing memory. We implemented a system which monitors the working set of virtual machines, reclaims unused memory and makes it available (as a remote swap device) for virtual machines which need memory. Our evaluations with HPC and Big Data benchmarks demonstrate the effectiveness of this approach. We show that remote memory can improve the performance of a standard Spark benchmark by up the 17 percent with an average performance degradation of 1.5 percent (for the providing application).

A Working-set Sensitive Page Replacement Policy for PCM-based Swap Systems

Due to the recent advances in Phage-Change Memory (PCM) technologies, a new memory hierarchy of computer systems with PCM is expected to appear. In this paper, we present a new page replacement policy that adopts PCM as a high speed swap device. As PCM has limited write endurance, our goal is to minimize the amount of data written to PCM. To do so, we defer the eviction of dirty pages in proportion to their dirtiness. However, excessive preservation of dirty pages in memory may deteriorate the page fault rate, especially when the memory capacity is not enough to accommodate full working-set pages. Thus, our policy monitors the current working-set size of the system, and controls the deferring level of dirty pages not to degrade the system performances. Simulation experiments show that the proposed policy reduces the write traffic to PCM by 160% without performance degradations.

Improving Cloud System Performances by Adopting Nvram-Based Storage Systems

NVRAM is being considered as an additional memory/storage component of future cloud computing systems. This paper investigates how much performance improvement can be obtained if we add NVRAM as the memory/storage media of cloud systems. As NVRAM is put on DDR slots, it is byte-accessible and hence can be used as a memory medium like DRAM. It can also be utilized as swap or journal devices if we use it as a block I/O device. We first consider NVRAM as a storage cache, and then, we measure the performance of systems that additionally use NVRAM as memory, swap, and journal devices. We use two workloads, I/O and memory intensive workloads. Our experiments show that using NVRAM as a journal device performs the best in I/O-intensive workload as it performs journaling I/O on NVRAM instead of slow storage. Using NVRAM as memory or swap devices does not show good results in I/O-intensive workload. However, in case of memory-intensive workload, NVRAM memory significantly improves the performance, and NVRAM swap also gains a certain level of improvement. We expect that our experiments will be helpful in the design of NVRAM-based cloud systems for memory or I/O intensive workload situations.

The Just-Meaningful Difference in Speech-to-Noise Ratio.

The speech-to-noise ratio (SNR) in an environment plays a vital role in speech communication for both normal-hearing (NH) and hearing-impaired (HI) listeners. While hearing-assistance devices attempt to deliver as favorable an SNR as possible, there may be discrepancies between noticeable and meaningful improvements in SNR. Furthermore, it is not clear how much of an SNR improvement is necessary to induce intervention-seeking behavior. Here, we report on a series of experiments examining the just-meaningful difference (JMD) in SNR. All experiments used sentences in same-spectrum noise, with two intervals on each trial mimicking examples of pre- and post-benefit situations. Different groups of NH and HI adults were asked (a) to rate how much better or worse the change in SNR was in a number of paired examples, (b) if they would swap the worse for the better SNR (e.g., their current device for another), or (c) if they would be willing to go to the clinic for the given increase in SNR. The mean SNR JMD based on better or worse ratings (one arbitrary unit) was similar to the just-noticeable difference, approximately 3 dB. However, the mean SNR JMD for the more clinically relevant tasks—willingness (at least 50% of the time) to swap devices or attend the clinic for a change in SNR—was 6 to 8 dB regardless of hearing ability. This SNR JMD of the order of 6 dB provides a new benchmark, indicating the SNR improvement necessary to immediately motivate participants to seek intervention.

PCM 기반 스왑 장치를 위한 클럭 기반 최소 쓰기 우선 교체 정책

본 논문은 PCM을 가상메모리 스왑 장치로 사용하는 시스템을 위한 새로운 페이지 교체 기법을 제안한다. 제안하는 기법은 메모리 내의 각 페이지에 대한 수정 정도를 고려해서 교체 대상 페이지를 선정하며 이를 통해 PCM에 발생시키는 쓰기량을 줄인다. 즉, 제안하는 기법은 페이지의 수정 정도를 서브페이지 단위로 관리하고 최근에 사용되지 않은 페이지 중 수정된 서브페이지의 수가 최소인 페이지를 교체한다. 트레이스를 이용한 재현 실험을 통해 제안한 기법이 기존 CLOCK 알고리즘 대비 평균 22.9% 최대 73.7%의 PCM 쓰기량을 절감함을 확인하였다. 또한 PCM의 수명과 에너지 소모율을 각각 평균 49.0%와 3.0% 개선함을 보였다.

LDF-CLOCK: The Least-Dirty-First CLOCK Replacement Policy for PCM-based Swap Devices

Phase-change memory (PCM) is a promising technology that is anticipated to be used in the memory hierarchy of future computer systems. However, its access time is relatively slower than DRAM and it has limited endurance cycle. Due to this reason, PCM is being considered as a high-speed storage medium (like swap device) or long-latency memory. In this paper, we adopt PCM as a virtual memory swap device and present a new page replacement policy that considers the characteristics of PCM. Specifically, we aim to reduce the write traffic to PCM by considering the dirtiness of pages when making a replacement decision. The proposed replacement policy tracks the dirtiness of a page at the granularity of a sub-page and replaces the least dirty page among pages not recently used. Experimental results with various workloads show that the proposed policy reduces the amount of data written to PCM by 22.9% on average and up to 73.7% compared to CLOCK. It also extends the lifespan of PCM by 49.0% and reduces the energy consumption of PCM by 3.0% on average.

Compressed memory swap for QoS of virtualized embedded systems

Virtualization has recently drawn attraction in smart consumer electronics as a way of completely isolating the main applications, which are in charge of the primary functionality of a device, from untrusted third-party applications. In a virtualized embedded device, flexible memory management is required to run multiple VMs efficiently on resource-constrained hardware. This paper presents an in-memory compressed swap device (CSW) for the virtualized consumer electronics environment. It swaps out only the memory of third-party applications in response to memory pressure on the main applications, to ensure its quality of service. To this end, CSW collaborates with memory ballooning, which is a scheme for dynamic memory partitioning between VMs. By compressing the swapped out memory pages, CSW can effectively provide memory to the main applications while preserving the availability of thirdparty applications. We implemented our scheme in a Xenbased virtualized system that has limited resources similar to conventional consumer electronics devices. The evaluation results show that CSW successfully provides memory to the main VM with a reasonable cost, while the third-party applications are not killed.

Label swapping device based on time-slot switching and planar lightwave circuit

A label swapping device based on a time-slot switching concept is proposed and demonstrated. It consists of two transversal-formed circuits fabricated on silica waveguides, and two optical gates. Its label swapping operation using 20 Gbit/s optical signals is successfully confirmed.

A very fast algorithm for RAM compression

Compressed virtual memory systems have been suggested, and in some cases implemented, to improve the effectiveness of use of physical RAM. However, most proposals and/or implementations are based on adaptive compression algorithms which achieve good compression ratios, but are slow compared to a local disk. Hence, they can only give some advantage with very slow (e.g. network-mounted) swap devices. In this paper we show that in many cases memory pages contain highly compressible data, with a very large amount of zero-valued elements. This suggests the replacement of slow, adaptive compression algorithms with very fast ones based on static Huffman codes.We present one such algorithm which, paired with a careful layout of the data, is able to compress 4KB pages at 40MB/s even when implemented in software on an inexpensive Pentium 100 system. We also show that the algorithm can achieve interesting compression ratios despite its simplicity.Since the compression/decompression speed of our algorithms exceeds disk bandwidth, its use in a compressed VM system can lead to both memory savings and speed improvements in servicing page faults. In this paper we discuss some possible applications of the algorithm in a compressed VM system.

Lot Scheduling in a Two-Machine Cell with Swapping Devices

This paper deals with the problem of part input sequencing in an automated flow shop system. The system consists of one input/output station, two machines and one AGV, which is used for all part transfer operations throughout the cell. The objective is the minimization of the makespan. This cell architecture has recently received considerable attention in the literature. Here we consider the case in which the two machines are equipped by a swapping device, allowing the AGV to exchange a new part for the one released by the machine. A similar device exists for the input/output station. If the transportation times are small enough, the problem can be formulated as a two-machine flow shop with limited intermediate buffer, which is NP-hard. Here we analyze the problem in the context of lot processing, i.e., when identical parts must be processed consecutively. Each set of identical parts forms a lot. The number of parts in the lot is the size of the lot. If the size of the ith lot is larger than a value b*i, ...