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Slab allocation
Slab allocation is a memory management mechanism intended for the efficient memory allocation of kernel objects. It eliminates fragmentation caused by allocations and deallocations. The technique is used to retain allocated memory that contains a data object of a certain type for reuse upon subsequent allocations of objects of the same type. It is analogous to an object pool, but only applies to memory, not other resources.
Slab allocation was first introduced in the Solaris 5.4 kernel by Jeff Bonwick.〔 It is now widely used by many Unix and Unix-like operating systems including FreeBSD〔(FreeBSD Kernel Developer's Manual )〕 and Linux.〔M. Tim Jones, (Anatomy of the Linux slab allocator )〕
== Basis ==
The primary motivation for slab allocation is that the initialization and destruction of kernel data objects can actually outweigh the cost of allocating memory for them.〔Jeff Bonwick,(The Slab Allocator: An Object-Caching Kernel Memory Allocator (1994) )〕 As object creation and deletion are widely employed by the kernel, overhead costs of initialization can result in significant performance drops. The notion of object caching was therefore introduced in order to avoid the invocation of functions used to initialize object state.
With slab allocation, memory chunks suitable to fit data objects of certain type or size are preallocated.〔Abraham Silberschatz ''et al.'': ''Operating system concepts''. Wiley: 2004. ISBN 0-471-69466-5〕 The slab allocator keeps track of these chunks, known as caches, so that when a request to allocate memory for a data object of a certain type is received, it can instantly satisfy the request with an already allocated slot. Destruction of the object does not free up the memory, but only opens a slot which is put in the list of free slots by the slab allocator. The next call to allocate memory of the same size will return the now unused memory slot. This process eliminates the need to search for suitable memory space and greatly alleviates memory fragmentation. In this context, a slab is one or more contiguous pages in the memory containing pre-allocated memory chunks.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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