The Unexpected Efficiency of Bin Packing Algorithms for Dynamic Storage Allocation in the Wild: An Intellectual Abstract

Recent work has shown that viewing allocators as black-box 2DBP solvers bears meaning. For instance, there exists a 2DBP-based fragmentation metric which often correlates monotonically with maximum resident set size (RSS). Given the field's indeterminacy with respect to fragmentation definitions, as well as the immense value of physical memory savings, we are motivated to set allocator-generated placements against their 2DBP-devised, makespan-optimizing counterparts. Of course, allocators must operate online while 2DBP algorithms work on complete request traces; but since both sides optimize criteria related to minimizing memory wastage, the idea of studying their relationship preserves its intellectual--and practical--interest. Unfortunately no implementations of 2DBP algorithms for DSA are available. This paper presents a first, though partial, implementation of the state-of-the-art. We validate its functionality by comparing its outputs' makespan to the theoretical upper bound provided by the original authors. Along the way, we identify and document key details to assist analogous future efforts. Our experiments comprise 4 modern allocators and 8 real application workloads. We make several notable observations on our empirical evidence: in terms of makespan, allocators outperform Robson's worst-case lower bound $93.75\%$ of the time. In $87.5\%$ of cases, GNU's \texttt{malloc} implementation demonstrates equivalent or superior performance to the 2DBP state-of-the-art, despite the second operating offline. Most surprisingly, the 2DBP algorithm proves competent in terms of fragmentation, producing up to $2.46$x better solutions. Future research can leverage such insights towards memory-targeting optimizations.Comment: 13 pages, 10 figures, 3 tables. To appear in ISMM '2

Conservation and building practice in a world heritage city : the case of Sana'a, Yemen

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Architecture, 2006.Includes bibliographical references (p. 480-497).The unique architecture of Sana'a, Yemen has been the focus of international conservation efforts, which have stimulated local interest and contributed to the formation of a local discourse. Because conservation followed so quickly on the heels of modernization, Sana'a provides an opportunity to study the interplay of these two global ideologies in the context of a strong local tradition of building. The "international" theory and practice of conservation developed in a specific cultural and intellectual context, that of modern Europe: it is based on the idea of an historic past that is radically different from the modern present. The artifacts of this past are frozen in time, relics of a past that has now been superseded. But the increasing museification of the built environment is untenable, and also incompatible with current notions of sustainability. Conservation in Sana'a and other cities in Yemen is unusual because the "historic past" is not so far in the past; in many cases, it is still part of the present. This provides not only an interesting case study, but an opportunity to reassess certain assumptions of international practice that are based on the idea of rupture between past and present, for example, the notions of historical value and authenticity.(cont.) In contrast to other studies of conservation, this dissertation does not focus on heritage as a project imposed by international agencies or by the state bureaucracy. Rather, it treats heritage as a discourse that is shaped on the ground by various actors, many of whom see themselves as representing the historic past. A unique approach has developed in Sana'a at the intersection of international and local practice, and it is this intersection that is the subject of the present work. The first chapter establishes the wider context of the project "site": it discusses the development of conservation theory and practice in Europe, with special attention to the idea of the historic city. Chapters two and three provide historical background on the development of the city of Sana'a and the UNESCO international safeguarding campaign of the 1980's. Chapters four and five take an ethnographic approach: they look at ways in which international practice has been understood and applied in the local context, by architects, builders, and residents. Chapter six traces the evolution of local discourse and practice through a series of projects, conducted with foreign assistance and by local organizations. The concluding chapter discusses the synthesis of international and local ideas and practices in Sana'a, and proposes policy directions based on this synthesis.by Michele Lamprakos.Ph.D

Architecture, memory and the future: The mosque-cathedral of Cordoba

La Gran Mezquita de Córdoba es uno de los monumentos más importantes de la civilización islámica y un famoso sitio en la lista del Patrimonio Mundial. Sin embargo, durante casi ocho siglos ha servido como la catedral de la ciudad. En tanto que otras mezquitas en la península Ibérica fueron finalmente demolidas y reemplazadas por iglesias y catedrales en algún momento posterior a la conquista castellana, la Gran Mezquita de Córdoba sobrevivió. Fue modificada para el culto católico, en una adaptación que culminó con la inserción de un gran coro y un presbiterio (crucero) en el siglo XVI. Esto produjo una imagen curiosa y dual que ha confundido, perturbado y fascinado a los visitantes durante siglos: el edificio es una catedral, pero parece una mezquita. Tras la inserción del crucero, la estructura fue progresivamente "cristianizada", aunque solo para ser "re-islamizada" en los siglos XIX al XX. El intento actual de la Iglesia por afianzar su control, y la resistencia que esto ha provocado entre los activistas cívicos, es solo el último episodio de una extraordinaria historia de 800 años. La confrontación sobre la fábrica e interpretación del edificio testimonia la poderosa continuidad del legado arquitectónico islámico. Pero también es un barómetro del cambio de actitudes hacia el pasado islámico, y el significado de ese mismo pasado para la cultura y la sociedad españolas.The Great Mosque of Córdoba is one of the foremost monuments of Islamic civilization and a famous World Heritage site.  But for almost eight centuries, it has served as the city’s cathedral. While other mosques on the Iberian peninsula were eventually demolished and replaced by churches and cathedrals at some point after the Castilian conquest, the Great Mosque of Cordoba survived.  It was modified for Catholic worship, culminating in the insertion of a massive choir and presbytery (crucero) in the sixteenth century.  This produced a curious, dual image that has confused, disturbed and fascinated visitors over the centuries: the building is a cathedral, but it looks like a mosque.  Following the insertion of the crucero, the fabric was progressively “christianized” – only to be “re-islamicized” in the 19th-20th centuries.  The Church’s current attempt to tighten its hold, and the resistance this has provoked among citizen activists, is just the latest episode in a remarkable 800-year story.  The struggle over the fabric and interpretation of the building attests to the continuing power of the Islamic architectural legacy.  But it is also a barometer of changing attitudes toward the Islamic past  –  and the meaning of that past for Spanish culture and society

Towards plug&play smart thermostats inspired by reinforcement learning

Buildings are immensely energy-demanding and this fact is enhanced by the expectation of even more increment of energy consumption in the future. In order to mitigate this problem, a low-cost, flexible and high-quality Decision-Making Mechanism for supporting the tasks of a Smart Thermostat is proposed. Energy efficiency and thermal comfort are the two primary quantities regarding control performance of a building's HVAC system. Apart from demonstrating a conflicting relationship, they depend not only on the building's dynamics, but also on the surrounding climate and weather, thus rendering the problem of finding a long-term control scheme hard, and of stochastic nature. The introduced mechanism is inspired by Reinforcement Learning techniques and aims at satisfying both occupants' thermal comfort and limiting energy consumption. In contrast to to existing methods, this approach focuses on a plug&play solution, that does not require detailed building models and is applicable to a wide variety of buildings as it learns the dynamics using gathered information from the environment. The proposed control mechanisms were evaluated via a well-known building simulation framework and implemented on ARM-based, low-cost embedded devices