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    <p> The slab allocator is an abstraction layer to make easier allocation of numerous objects of a same type. The interface offers the function</p> <pre class="lang-c prettyprint-override"><code>struct kmem_cache * kmem_cache_create(const char *name, size_t size, size_t align, unsigned long flags, void (*ctor)(void*)); </code></pre> <p>This function creates a new slab allocator that will be able to handle allocation of <code>size</code>-bytes long objects. If the creation is successful, you get your pointer to the related <code>struct kmem_cache</code>. This structures holds information about the <em>slabs</em> it manages.</p> <p>As it is implied on the Wikipedia description, the purpose of such an extra layer is to prevent memory fragmentation issues that could happen if the memory allocation was made in a simple and intuitive manner. To do so, it introduces the notion of <em>slab</em> through the following data structure :</p> <pre class="lang-c prettyprint-override"><code>struct slab { struct list_head list; /* embedded list structure */ unsigned long colouroff; void *s_mem; /* first object in the slab */ unsigned int inuse; /* allocated objects in the slab */ kmem_bufctl_t free; /* first free object (if any) */ }; </code></pre> <p>Thus, the <code>kmem_cache</code> object holds 3 lists of its <em>slabs</em>, gathered in 3 flavours :</p> <ul> <li>Empty slabs : these slabs do not contain an in-use object.</li> <li>Partial slabs : these slabs contain objects currently used but there is still memory area that can hold new objects.</li> <li>Full slabs : these slabs contains objects being used and cannot host new objects (full ...).</li> </ul> <p>When requesting an object through the slab allocator, it will try to get the required memory area within a partial slab, if it cannot, it will get it from an empty slab.</p> <p>If you are eager to collect more information about this, you should take a look at Robert Love's <a href="http://rads.stackoverflow.com/amzn/click/0672329468" rel="nofollow"><em>Linux Kernel Development</em></a></p>
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