diff options
Diffstat (limited to 'Documentation/vm/z3fold.txt')
| -rw-r--r-- | Documentation/vm/z3fold.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/Documentation/vm/z3fold.txt b/Documentation/vm/z3fold.txt new file mode 100644 index 000000000000..38e4dac810b6 --- /dev/null +++ b/Documentation/vm/z3fold.txt @@ -0,0 +1,26 @@ +z3fold +------ + +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. |