PDL Talk Series

July 27, 2023

TIME: 12:00 noon - to approximately 1:00 pm EDT
PLACE: Virtual - a zoom link will be emailed closer to the seminar

SPEAKER: Dimitrios Skarlatos
Assistant Professor, CSD, Carnegie Mellon University

Contiguitas: The Pursuit of Physical Memory Contiguity in Datacenters
The unabating growth of the memory needs of emerging datacenter applications has exacerbated the scalability bottleneck of virtual memory. However, reducing the excessive overhead of address translation will remain onerous until the physical memory contiguity predicament gets resolved. To address this problem, this paper presents Contiguitas, a novel redesign of memory management in the operating system and hardware that provides ample physical memory contiguity. We identify that the primary cause of memory fragmentation in Meta’s datacenters is unmovable allocations scattered across the address space that impede large contiguity from being formed. To provide ample physical memory contiguity by design, Contiguitas first separates regular movable allocations from unmovable ones by placing them into two different continuous regions in physical memory and dynamically adjusts the boundary of the two regions based on memory demand. Drastically reducing unmovable allocations is challenging because the majority of unmovable pages cannot be moved with software alone given that access to the page cannot be blocked for a migration to take place. Furthermore, page migration is expensive as it requires a long downtime to (a) perform TLB shootdowns that scale poorly with the number of victim TLBs, and (b) copy the page. To this end, Contiguitas eliminates the primary source of unmovable allocations by introducing hardware extensions in the last-level cache to enable the transparent and efficient migration of unmovable pages even while the pages remain in use.

BIO: Dimitrios is an assistant professor in the Computer Science Department at Carnegie Mellon University. His research bridges computer architecture and operating systems with a focus on performance, security, and scalability. He has received several awards for his cross-cutting research including the NSF CAREER award, four Meta Faculty Awards in systems and security, the joint 2021 ACM SIGARCH & IEEE CS TCCA Outstanding Dissertation award, the David J. Kuck Outstanding Ph.D. Thesis Award, an ISCA Best Paper Award, two ASPLOS Best Paper Awards, and three IEEE MICRO Top Picks. Dimitrios has released several open-source frameworks, with some of his work upstreamed in Linux and Android and deployed in production at Meta.

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