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CSE 490dp Resource Control. Robert Grimm. Problems. How to access resources? Basic usage tracking How to measure resource consumption? Accounting How to limit resource consumption? Policy We only cover first two issues. Resource Access. Issue How to track usage? Four models
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CSE 490dpResource Control Robert Grimm
Problems • How to access resources? • Basic usage tracking • How to measure resource consumption? • Accounting • How to limit resource consumption? • Policy • We only cover first two issues
Resource Access • Issue • How to track usage? • Four models • Don’t do it • Explicit creation and deletion • Automatic reclamation of unused resources • Leases
Don’t Do It • Example: NFS [Ousterhout 90] • Most operations are idempotent • No connection state • “Stateless” • Files persist • “Stateful” by definition of a file system
Advantages • Crash handling • No recovery on server • No reboots on client • Simplicity • No connection handling • No recovery code
Problems • Performance • No client-side caching • Consistency • Clients don’t know about others modifying same file • Semantics • Not implemented: locks • Not idempotent: mkdir
Explicit Creation and Deletion • Example: Connections in Sprite FS [Ousterhout 90] • Advantages • Consistency • Server ensures only one writer per file • Performance • Client-side caching • No synchronous writes to server • Files may be overwritten / deletedbefore they get sent to server
Problems • Complexity • More to do on server • Recovery • How to restore connections after failure? • Performance • Explicit open and close operations • Space overheads • Per-connection state
Pervasive Paradigm • new / delete • C, C++ • create / delete • Files • Tuples in T Spaces, one.world • run / kill • Applications, servers
Automatic Reclamation • Garbage collection • Basic idea • Keep track of used resources • Automatically reclaim unused resourcesin background • Examples • Locally for Java • Distributed for Java RMI
Discussion • Advantage • No need to worry about deletion • Problem • Complete and reliable usage information is hard to come by • Network connections and nodes fail • May depend on human factors • Hard to automate
Discussion • Can we automate creation and deletion? • Cluster-based service • Automatically run and kill serviceson individual nodes
Leases • Basic idea • Limit resource access by time-out • Reclaim resource after time-out expires • Operations • Acquire (open) • Renew • Cancel (close)
Examples • Remote resources • Java RMI • Jini’s remote events, transactions • File cache • V [Gray & Cheriton 89] • Storage • JavaSpaces • Resource access in general • one.world
Problem • A resource can always vanish • Lease renewal is delayed • E.g., message may be delayed, is lost • Lease expires
Tracking Usage • Don’t do it • Explicit creation and deletion • Garbage collection • Automate deletion based on usage • Leases • Automate deletion based on time-out
Resources • Transient • Objects, connections • Services • Applications • User data • Files, tuples
Resource Accounting • Problem • Traditionally, process represents • Protection domain • Resource principal • But, modern servers don’t follow this model • [Banga et al., 99]
HTTP Server Implementations • One process per connection • Event-based server • Multi-threaded server
Scheduling Entities and Activities • Classical application • Single process • Mostly user space • Modern applications • Considerable kernel processing • Multiple processes • Multiple threads
How to Account for Resources? • Introduce new abstraction • Resource container • Tracks usage information • CPU time • Memory • Networking bandwidth • … • Orthogonal to scheduling entities • Threads, processes have resource binding
Scheduler Binding • Problem • How to schedule threads that are bound to several resource containers? • E.g., event-based server • Solution • Scheduler binding • Set of all resource containers
Operations • Create • Set parent • Hierarchy of containers • Release • Reference counted • Share • Access attributes • Access usage information
Operations • Bind thread to a container • Reset scheduler binding • Bind socket, file to a container
Usage • One resource container per logical job • Create new container when accepting connection • Change thread’s container as necessary • Example policy • Different classes of clients, depending on source IP address • Low priority • High priority
Performance • Growing number of low priority clients
Performance • Growing number of concurrent CGI requests
Performance • Growing SYN-flood rate
Summary • Resource accounting is orthogonal to • Protection • Scheduling • Need explicit abstraction • Resource containers
Issues • How to express and enforce policies? • How to make resource containers scale across the network?