Global memory management in a workstation cluster

take-away

• Global memory
• Global LRU (probabilistic algo)

Overview

architecture

• global memory management in a cluster of machines connected by a high-speed LAN

• GMS (global memory service)

  • local and global page
  • algorithm
  • how to determine what to replace
    • global information
    • epoch (timeout and M pages to replace)
      • flush TLB
      • assign probabilities (lottery scheduling)
• compared to today’s system
  • In contrast, each operating system in today’s clusters acts as an autonomous agent, exporting services to other nodes, but not acting in a coordinated way.
• For example, global memory management allows the operating system to use cluster-wide memory to avoid many disk accesses

Goal

• minimize average data reference time

  • go to remote memory instead of disks

• Why can global memory management benefit application?

  • many nodes in LAN are often idle
  • use those idle resources on behalf of nodes with active application
  • GMS: use idle memory resources

Algorithm

• Model:
  • local pages and global pages
  • global pages are pages stroed on behalf of other nodes
  • global pages together constitute “global memory”
  • global memory adds another level of memory hierarchy

Implementation

• Three main aspects to implementation
  • maintaining page ages
  • finding pages in cluster
  • making replacement and eviction (逐出) decisions

Page Ages

• global page ages?
  • As times goes on
• local page ages?
  • File pages easy
  • Need to track accesses to mapped pages
• Use similar trick as in Ozalp’s paper

Global LRU

• There is too much overhead to maintain a global age. Instead, a probabilistic algorithm is used to decide which one to page out.

Making Replacement Decisions

• Common case is replacing oldest page in global memory
• the algorithm in paper?

How to design your experiments?

• The objective: Convince others and yourself about the idea and the system
• Question you should ask yourself
  • Given your idea and your system, what kind of would others have about the idea and the system?
  • Pick the Grapevine system as an example to design experimental evaluation for them