The slab allocator: an object-caching kernel memory allocator . Jeff Bonwick, Jonathan Adams, Magazines and Vmem: Extending the Slab. Implementation of the Slab Allocator as described in “The Slab Allocator: An Object-Caching Kernel Memory Allocator” by Jeff Bonwick. – lucastsa/ slab_allocator. This package provides a simple implementation of a Slab memory allocator (Jeff Bonwick: “The Slab Allocator: An Object-Caching Kernel Memory Allocator”).

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The new object gets allocated from this slab, and its location becomes marked as “partial”. The reason for the large slabs having a different layout from the small slabs is that it allows large slabs to pack better into page-size units, which helps with fragmentation. Slab allocation is a memory management mechanism intended for the efficient memory allocation of kernel objects.

A small slab is exactly one page, and has a defined structure that allows bufctls to be avoided. Slab allocation was first introduced in the Solaris 2. The slab contains a list of bufctls, which are simply controllers for each buffer that can be allocated a buffer is the memory that the user of a slab allocator would use. It represents one memory allocation to the cache from the machine, and whose size is customarily a multiple of the page size. It is analogous to an object poolbut only applies to memory, not other resources.

This page was last edited on 23 Decemberat 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. From Wikipedia, the free encyclopedia.

Advanced Search Include Citations. 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. This allows the small slab’s bufctl to be bypassed. The last part of the page contains the ‘slab header’, which is the information needed to retain the slab. The notion of object caching was therefore introduced in order to avoid the invocation of functions used to initialize object state.


This number depends on the size of the associated slabs. However, in many cases the cost of initializing and destroying the object exceeds the cost of allocating and freeing mem This allocator is based on a set of object-caching primitives that reduce the cost of allocating complex objects by retaining their state between uses.

The discussion page may contain suggestions. The allocator’s object bonwicck respond dynamically to global memory pressure, and employ an objectcoloring scheme that improves the system’s overall cache utilization and bus balance. Not to be confused with Slab unit.

By using this site, you agree to the Terms of Use and Privacy Policy. Views Read Edit View history. Instead of using bufctls, we use the buffers themselves to retain the free list links.

Retrieved 18 November 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. A fast kernel memory allocator is therefore essential.

Slab allocation

When the process calls for a new kernel object, the system tries to find a free location for that object on a partial slab allocaator a cache for that type of object. The allocator also has several statistical and debugging features that can detect a wide range of problems throughout the system.

Initially, the system marks each slab as “empty”. Retrieved 28 December With slab allocation, memory chunks suitable to fit aallocator objects of certain type or size are preallocated.

If no such location exists, the system allocates a new slab from contiguous physical pages and assigns it to a cache. Retrieved from ” https: When a program sets up a cache, it allocates a number of objects to the slabs associated with that cache. These same primitives prove equally effective for managing stateless memory e.


This article may need to be rewritten entirely to comply with Wikipedia’s quality standards. In this context, a slab is one or more contiguous pages in the memory containing pre-allocated memory chunks.

A slab is the amount by which a cache can grow or shrink.

CiteSeerX — The Slab Allocator: An Object-Caching Kernel Memory Allocator

Abstract This paper presents a comprehensive design overview of the SunOS 5. Advanced Search Include Citations Disambiguate. It eliminates fragmentation caused by allocations and deallocations. Starting at the first address of that page, there are as many buffers as can be allocated without running into jfef slab header at the end of the page.

A slab must contain a list of free buffers or bufctlsas well as jeft list of the bufctls that have been allocated in the case of a large slab size.

Slab Allocator | Oracle Jeff Bonwick’s Blog

The allocation takes place quickly, because the system builds the objects in advance and readily allocates them from a slab. Introduction The allocation and freeing of objects are among the most common operations in the kernel.

These small slabs need to be optimized further from the logical layout, by avoiding using bufctls which would be just as large as the data itself and cause memory usage to be much jefd. This process eliminates the need to search for suitable memory space and greatly alleviates memory fragmentation.

The next call to allocate memory of the same size will return the now unused memory slot. Webarchive template wayback links Use dmy dates from August Wikipedia articles needing rewrite from May All articles needing rewrite All articles with unsourced statements Articles with unsourced statements from April