|z3fold is a special purpose allocator for storing compressed pages.
|It is designed to store up to three compressed pages per physical page.
|It is a zbud derivative which allows for higher compression
|ratio keeping the simplicity and determinism of its predecessor.
|The main differences between z3fold and zbud are:
|* unlike zbud, z3fold allows for up to PAGE_SIZE allocations
|* z3fold can hold up to 3 compressed pages in its page
|* z3fold doesn't export any API itself and is thus intended to be used
| via the zpool API.
|To keep the determinism and simplicity, z3fold, just like zbud, always
|stores an integral number of compressed pages per page, but it can store
|up to 3 pages unlike zbud which can store at most 2. Therefore the
|compression ratio goes to around 2.7x while zbud's one is around 1.7x.
|Unlike zbud (but like zsmalloc for that matter) z3fold_alloc() does not
|return a dereferenceable pointer. Instead, it returns an unsigned long
|handle which encodes actual location of the allocated object.
|Keeping effective compression ratio close to zsmalloc's, z3fold doesn't
|depend on MMU enabled and provides more predictable reclaim behavior
|which makes it a better fit for small and response-critical systems.