Commit 9a001fc1 authored by Vitaly Wool's avatar Vitaly Wool Committed by Linus Torvalds
Browse files

z3fold: the 3-fold allocator for compressed pages 

This patch introduces z3fold, 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.

This patch comes as a follow-up to the discussions at the Embedded Linux
Conference in San-Diego related to the talk [1].  The outcome of these
discussions was that it would be good to have a compressed page
allocator as stable and deterministic as zbud with with higher
compression ratio.

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 2.6x while zbud's one is around 1.7x.

The patch is based on the latest linux.git tree.

This version has been updated after testing on various simulators (e.g.
ARM Versatile Express, MIPS Malta, x86_64/Haswell) and basing on
comments from Dan Streetman [3].

[1] https://openiotelc2016.sched.org/event/6DAC/swapping-and-embedded-compression-relieves-the-pressure-vitaly-wool-softprise-consulting-ou
[2] https://lkml.org/lkml/2016/4/21/799
[3] https://lkml.org/lkml/2016/5/4/852

Link: http://lkml.kernel.org/r/20160509151753.ec3f9fda3c9898d31ff52a32@gmail.com


Signed-off-by: default avatarVitaly Wool <vitalywool@gmail.com>
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d5ee7c3b

Documentation/vm/z3fold.txt

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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.

mm/Kconfig

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@@ -567,7 +567,7 @@ config ZPOOL 
	  zsmalloc.

	  zsmalloc.





config ZBUD

config ZBUD

	tristate "Low density storage for compressed pages"

	tristate "Low (Up to 2x) density storage for compressed pages"

	default n

	default n

	help

	help

	  A special purpose allocator for storing compressed pages.

	  A special purpose allocator for storing compressed pages.
@@ -576,6 +576,16 @@ config ZBUD 
	  deterministic reclaim properties that make it preferable to a higher

	  deterministic reclaim properties that make it preferable to a higher

	  density approach when reclaim will be used.

	  density approach when reclaim will be used.





config Z3FOLD

	tristate "Up to 3x density storage for compressed pages"

	depends on ZPOOL

	default n

	help

	  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 so the simplicity and determinism are

	  still there.



config ZSMALLOC

config ZSMALLOC

	tristate "Memory allocator for compressed pages"

	tristate "Memory allocator for compressed pages"

	depends on MMU

	depends on MMU

mm/Makefile

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@@ -89,6 +89,7 @@ obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o 
obj-$(CONFIG_ZPOOL)	+= zpool.o

obj-$(CONFIG_ZPOOL)	+= zpool.o

obj-$(CONFIG_ZBUD)	+= zbud.o

obj-$(CONFIG_ZBUD)	+= zbud.o

obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o

obj-$(CONFIG_ZSMALLOC)	+= zsmalloc.o

obj-$(CONFIG_Z3FOLD)	+= z3fold.o

obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o

obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o

obj-$(CONFIG_CMA)	+= cma.o

obj-$(CONFIG_CMA)	+= cma.o

obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o

obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o

mm/z3fold.c

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