Okay, we begin with the first of these design ideas – the notion of a cache of common objects. A long time ago, a SunOS developer, Jeff Bonwick, noticed that certain kernel objects – data structures, typically – were allocated and deallocated frequently within the OS. He thus had the idea of pre-allocating them in a cache of sorts. This evolved into what we call the slab cache.
Thus, on the Linux OS as well, the kernel (as part of the boot time initialization) pre-allocates a fairly large number of objects into several slab caches. The reason: performance! When core kernel code (or a device driver) requires memory for one of these objects, it directly requests the slab allocator. If cached, the allocation is almost immediate (the converse being true as well at deallocation). You might wonder, is all this really necessary? Indeed it is!
A good example of high performance being required is within the critical code paths of the network and...
