Memory allocation in the kernel – which APIs to use when

A really quick summary of what we have learned so far: the kernel’s underlying engine for memory allocation (and freeing) is called the page (or buddy system) allocator. Ultimately, every single memory allocation (and subsequent free) goes through this layer. It has its share of problems, though, the chief one being internal fragmentation or wastage (due to its minimum granularity being a page or multiple pages). Thus, we have the slab allocator (or slab cache) layered above it, providing the power of object caching and caching fragments of a page (helping alleviate the page allocator’s wastage issues). Also, don’t forget that you can create your own custom slab caches. Further, the kernel has a vmalloc region and APIs to allocate large virtual memory swathes from within it.

With this information in mind, let’s move along. To understand which API to use when, let’s first look at...