From ad56b738c5dd223a2f66685830f82194025a6138 Mon Sep 17 00:00:00 2001 From: Mike Rapoport Date: Wed, 21 Mar 2018 21:22:47 +0200 Subject: docs/vm: rename documentation files to .rst Signed-off-by: Mike Rapoport Signed-off-by: Jonathan Corbet --- Documentation/vm/z3fold.rst | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) create mode 100644 Documentation/vm/z3fold.rst (limited to 'Documentation/vm/z3fold.rst') diff --git a/Documentation/vm/z3fold.rst b/Documentation/vm/z3fold.rst new file mode 100644 index 000000000000..224e3c61d686 --- /dev/null +++ b/Documentation/vm/z3fold.rst @@ -0,0 +1,30 @@ +.. _z3fold: + +====== +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. -- cgit v1.2.3