The SLAB allocator allows to create caches, which contains a set of objects of the same size
The object size can be smaller or greater than the page size
The SLAB allocator takes care of growing or reducing the size of the cache as needed, depending on the number of allocated objects. It uses the page allocator to allocate and free pages.
SLAB caches are used for data structures that are present in many many instances in the kernel: directory entries, file objects, network packet descriptors, process descriptors, etc.