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- z3fold
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- 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.
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