Distributed shared memory
Encyclopedia
Distributed Shared Memory (DSM), in Computer Architecture
is a form of memory architecture where the (physically separate) memories can be addressed as one (logically shared) address space. Here, the term shared does not mean that there is a single centralized memory but shared essentially means that the address space is shared (same physical address on two processors refers to the same location in memory). Alternatively in computer science
it is known as (DGAS), a concept that refers to a wide class of software and hardware implementations, in which each node
of a cluster has access to shared memory
in addition to each node's non-shared private memory
.
Software DSM systems can be implemented in an operating system, or as a programming library. Software DSM systems implemented in the operating system can be thought of as extensions of the underlying virtual memory
architecture. Such systems are transparent to the developer; which means that the underlying distributed memory
is completely hidden from the users. In contrast, Software DSM systems implemented at the library or language level are not transparent and developers usually have to program differently. However, these systems offer a more portable approach to DSM system implementation.
Software DSM systems also have the flexibility to organize the shared memory region in different ways. The page based approach organizes shared memory into pages of fixed size. In contrast, the object based approach organizes the shared memory region as an abstract space for storing shareable objects of variable sizes. Another commonly seen implementation uses a tuple space
, in which the unit of sharing is a tuple
.
Shared memory
architecture may involve separating memory into shared parts distributed amongst nodes and main memory; or distributing all memory between nodes. A coherence protocol, chosen in accordance with a consistency model
, maintains memory coherence
.
Examples of such systems include:
Computer architecture
In computer science and engineering, computer architecture is the practical art of selecting and interconnecting hardware components to create computers that meet functional, performance and cost goals and the formal modelling of those systems....
is a form of memory architecture where the (physically separate) memories can be addressed as one (logically shared) address space. Here, the term shared does not mean that there is a single centralized memory but shared essentially means that the address space is shared (same physical address on two processors refers to the same location in memory). Alternatively in computer science
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
it is known as (DGAS), a concept that refers to a wide class of software and hardware implementations, in which each node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
of a cluster has access to shared memory
Shared memory
In computing, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Depending on context, programs may run on a single processor or on multiple separate processors...
in addition to each node's non-shared private memory
Random-access memory
Random access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
.
Software DSM systems can be implemented in an operating system, or as a programming library. Software DSM systems implemented in the operating system can be thought of as extensions of the underlying virtual memory
Virtual memory
In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
architecture. Such systems are transparent to the developer; which means that the underlying distributed memory
Distributed memory
In computer science, distributed memory refers to a multiple-processor computer system in which each processor has its own private memory. Computational tasks can only operate on local data, and if remote data is required, the computational task must communicate with one or more remote processors...
is completely hidden from the users. In contrast, Software DSM systems implemented at the library or language level are not transparent and developers usually have to program differently. However, these systems offer a more portable approach to DSM system implementation.
Software DSM systems also have the flexibility to organize the shared memory region in different ways. The page based approach organizes shared memory into pages of fixed size. In contrast, the object based approach organizes the shared memory region as an abstract space for storing shareable objects of variable sizes. Another commonly seen implementation uses a tuple space
Tuple space
A tuple space is an implementation of the associative memory paradigm for parallel/distributed computing. It provides a repository of tuples that can be accessed concurrently. As an illustrative example, consider that there are a group of processors that produce pieces of data and a group of...
, in which the unit of sharing is a tuple
Tuple
In mathematics and computer science, a tuple is an ordered list of elements. In set theory, an n-tuple is a sequence of n elements, where n is a positive integer. There is also one 0-tuple, an empty sequence. An n-tuple is defined inductively using the construction of an ordered pair...
.
Shared memory
Shared memory
In computing, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Depending on context, programs may run on a single processor or on multiple separate processors...
architecture may involve separating memory into shared parts distributed amongst nodes and main memory; or distributing all memory between nodes. A coherence protocol, chosen in accordance with a consistency model
Consistency model
In computer science, consistency models are used in distributed systems like distributed shared memory systems or distributed data stores . The system supports a given model, if operations on memory follow specific rules...
, maintains memory coherence
Memory coherence
Memory coherence is an issue that affects the design of computer systems in which two or more processors or cores share a common area of memory....
.
Examples of such systems include:
- KerrighedKerrighedKerrighed is an open source single-system image cluster software project. The project started in October 1998 at the Paris research group The French National Institute for Research in Computer Science and Control.-Background:...
- OpenSSIOpenSSIOpenSSI is an open source single-system image clustering system. It allows a collection of computers to be treated as one large system, allowing applications running on any one machine access to the resources of all the machines in the cluster....
- MOSIXMOSIXMOSIX is a distributed operating system. Although early versions were based on older UNIX systems, since 1999 it focuses on Linux clusters and grids...
- TreadMarksTreadMarksTreadMarks is a distributed shared memory system created at Rice University in the 1990s.-External links:*...
- DIPC
External links
- Distributed Shared Cache
- Memory coherence in shared virtual memory systems by Kai Li, Paul Hudak published in ACM Transactions on Computer Systems, Volume 7 Issue 4, Nov. 1989