Migration
Movement Process of a currently executing process to a new processor Process migration mechanism how the system migrates a process from source to destination
Homogenous Heterogeneous Distributed shared memory
Remote execution process execution on a new machine Load balancing policy when and where to transfer a process
E.g., CPU resource, network bandwidth
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Example : Heart Transplant
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Metrics of Process Migration
Process migration time
The time from issuing the migration request until the process can execute on the new machine
Excision time
The time it takes for the process of extracting process information from the operating system kernel
Insertion
The time it takes for the process to insert process information to the operating system kernel
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What needs to be migrated?
Process control information
Priority, state, process ID, parent process ID
Execution state
Processor state, registers, stack pointer, program counter
Address space
The entire virtual memory of the process
Message
Buffer messages, e.g., in the network stack or from other processes
File information
Can all processes be migrated?
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Process Migration Algorithms
Total copy
As its name suggests Simple Heavy overhead
Demand page
No virtual memory pages Transfer on demand in case of page faults
File Server
Introduce a third server
Freeze free
Send current code, stack and the current heap page Separate process state from the state of communication links, the later is migrate separately
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OS Virtualization in MobiDesk
Each session gets its own virtual private namespace
Virtual: all OS resources are accessed through virtual identifiers Private: only processes within session can see the namespace
Virtualization layer associate a virtual name with the OS physical name Traps all calls to OS and translates names
System call interposition: wrappers around system calls that translate names virtual to physical names and prevent accesses across the session boundary chroot and file system stacking to provide each session with its own file system namespace
Reminds of cygwin?
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OS Virtualization in MobiDesk(Contd)
Migration of session
Use check-point restart
Suspend the session Save high-level representation Digital signed and transfer to another machine
Only applicable to the same platform, may accommodate different kernel version
Comments:
Software like VMWare, Windows Virtual Desktop provides virtualization of entire OS and allows running applications compiled for one platform to run another platform but sessions cannot be migrated across platforms
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Network Virtualization in MobiDesk
Issues
Multiple sessions on the same server may run the same service Ongoing network connections must be preserved when a session is migrated from one server to another
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Case 1: All servers on same subnet
Solutions:
Each session gets an IP address from the DHCP server Uses it as an alias on the NIC on the attached physical machine Gratuitous ARP is used to resolve MAC address change when sessions are migrated Proxy...