Youngjin Kwon

Current hardware and application storage trends put immense pressure on the operating system's storage subsystem. On the hardware side, the market for storage devices has diversified to a multi-layer storage topology spanning multiple orders of magnitude in cost and performance. Above the file system, applications increasingly need to process small, random IO on vast data sets with low latency, high throughput, and simple crash consistency. File systems designed for a single storage layer cannot

Modern computing is hungry for RAM, with today's enormous capacities eagerly consumed by diverse workloads. Hardware address translation overheads have grown with memory capacity, motivating hardware manufacturers to provide TLBs with thousands of entries for large page sizes (called huge pages). Operating systems and hypervisors support huge pages with a hodge-podge of best-effort algorithms and spot fixes that made sense for architectures with limited huge page support, but the time has come f

In multi-tenant systems, the CPU overhead of distributed file systems (DFSes) is increasingly a burden to application performance. CPU and memory interference cause degraded and unstable application and storage performance, in particular for operation latency. Recent client-local DFSes for persistent memory (PM) accelerate this trend. DFS offload to SmartNICs is a promising solution to these problems, but it is challenging to fit the complex demands of a DFS onto simple SmartNIC processors locat

Large commercial latency-sensitive services, such as web search, run on dedicated clusters provisioned for peak load to ensure responsiveness and tolerate data center outages. As a result, the average load is far lower than the peak load used for provisioning, leading to resource under-utilization. The idle resources can be used to run batch jobs, completing useful work and reducing overall data center provisioning costs. However, this is challenging in practice due to the complexity and stringe

The availability of large pages has dramatically improved the efficiency of address translation for applications that use large contiguous regions of memory. However, large pages can be difficult to allocate due to fragmented memory, non-movable pages, or the need to split a large page into regular pages when part of the large page is forced to have a different permission status from the rest of the page. Furthermore, they can also be expensive due to memory bloating caused by sparse accesses to

In this paper, a fault location algorithm using travelling waves and a cross correlation method is proposed for HVDC cable lines. The arriving instants of the first fault-induced transient backward travelling wave and its subsequent reflected wave can be detected by using a cross correlation method. The fault distance is estimated by using the time difference between the two instants of incident waves and the velocity of the travelling wave. Because the fault-induced backward wave is much simila

Performance-asymmetric multi-cores consist of heterogeneous cores, which support the same ISA, but have different computing capabilities. To maximize the throughput of asymmetric multi-core systems, operating systems are responsible for scheduling threads to different types of cores. However, system virtualization poses a challenge for such asymmetric multi-cores, since virtualization hides the physical heterogeneity from guest operating systems. In this paper, we explore the design space of hyp

Sego is a hypervisor-based system that gives strong privacy and integrity guarantees to trusted applications, even when the guest operating system is compromised or hostile. Sego verifies operating system services, like the file system, instead of replacing them. By associating trusted metadata with user data across all system devices, Sego verifies system services more efficiently than previous systems, especially services that depend on data contents. We extensively evaluate Sego's performance

Memory capacity and demand have grown hand in hand in recent years. However, overheads for memory virtualization, in particular for address translation, grow with memory capacity as well, motivating hardware manufacturers to provide TLBs with thousands of entries for larger pages, or huge pages. Current OSes and hypervisors support huge pages with a hodge-podge of best-effort algorithms and spot fixes that make less and less sense as architectural support for huge pages matures. The time has com

Let <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>R</mml:mi> </mml:math> be a smooth Riemannian manifold of finite volume, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Δ</mml:mi> </mml:math> its Laplace (-Beltrami) operator. Canonical direct-sum decompositions of certain subspaces of the Wiener and Royden algebras of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>R</mml:mi> </mml:math> are found, and for biharmonic functions (those for

Sego is a hypervisor-based system that gives strong privacy and integrity guarantees to trusted applications, even when the guest operating system is compromised or hostile. Sego verifies operating system services, like the file system, instead of replacing them. By associating trusted metadata with user data across all system devices, Sego verifies system services more efficiently than previous systems, especially services that depend on data contents. We extensively evaluate Sego's performance

1. The classification of Riemann surfaces with respect to the equation Δu = Pu ( P ≥ 0, P ≢ 0) was initiated by Ozawa [13] and further developed by L. Myrberg [8, 9], Royden [14], Nakai [10, 11], Sario-Nakai [15], Nakai-Sario [12], Glasner-Katz [3], and Kwon-Sario [7].

Sego is a hypervisor-based system that gives strong privacy and integrity guarantees to trusted applications, even when the guest operating system is compromised or hostile. Sego verifies operating system services, like the file system, instead of replacing them. By associating trusted metadata with user data across all system devices, Sego verifies system services more efficiently than previous systems, especially services that depend on data contents. We extensively evaluate Sego's performance

The P -harmonic boundary Δ P and the P -singular point s of a Riemannian manifold R have been shown to play an important role in the study of bounded energy-finite solutions of Δu = Pu (Nakai-Sario [7], Kwon-Sario [4], Kwon-Sario-Schiff [5]). The objective of the present paper is to establish, in terms of Δ P and s, properties of unbounded energy-finite solutions ( PE -functions) and of limits of decreasing sequences of positive PE -functions ( -functions). Also, PE- and -minimal functions will

Conventional phasor estimation methods can causes error if the envelope of the signal is changed according to time. In this paper, a modified dynamic phasor estimation method was proposed to overcome the disadvantages of conventional phasor estimation methods. To evaluate the performance of the proposed method, a fault location algorithm which uses the proposed phasor estimation method was tested over varying fault distances and fault resistances. The fault location result using the proposed pha