mm: remove unused zpool layer

evict pages from its own compressed pool on an LRU basis and write them back to

the backing swap device in the case that the compressed pool is full.

Zswap makes use of zpool for the managing the compressed memory pool.  Each

allocation in zpool is not directly accessible by address.  Rather, a handle is

Zswap makes use of zsmalloc for the managing the compressed memory pool.  Each

allocation in zsmalloc is not directly accessible by address.  Rather, a handle is

returned by the allocation routine and that handle must be mapped before being

accessed.  The compressed memory pool grows on demand and shrinks as compressed

pages are freed.  The pool is not preallocated.  By default, a zpool

of type selected in ``CONFIG_ZSWAP_ZPOOL_DEFAULT`` Kconfig option is created,

but it can be overridden at boot time by setting the ``zpool`` attribute,

e.g. ``zswap.zpool=zsmalloc``. It can also be changed at runtime using the sysfs

``zpool`` attribute, e.g.::

	echo zsmalloc > /sys/module/zswap/parameters/zpool

The zsmalloc type zpool has a complex compressed page storage method, and it

can achieve great storage densities.

pages are freed.  The pool is not preallocated.

When a swap page is passed from swapout to zswap, zswap maintains a mapping

of the swap entry, a combination of the swap type and swap offset, to the zpool

handle that references that compressed swap page.  This mapping is achieved

with a red-black tree per swap type.  The swap offset is the search key for the

tree nodes.

of the swap entry, a combination of the swap type and swap offset, to the

zsmalloc handle that references that compressed swap page.  This mapping is

achieved with a red-black tree per swap type.  The swap offset is the search

key for the tree nodes.

During a page fault on a PTE that is a swap entry, the swapin code calls the

zswap load function to decompress the page into the page allocated by the page

	echo lzo > /sys/module/zswap/parameters/compressor

When the zpool and/or compressor parameter is changed at runtime, any existing

compressed pages are not modified; they are left in their own zpool.  When a

request is made for a page in an old zpool, it is uncompressed using its

original compressor.  Once all pages are removed from an old zpool, the zpool

and its compressor are freed.

When the compressor parameter is changed at runtime, any existing compressed

pages are not modified; they are left in their own pool.  When a request is

made for a page in an old pool, it is uncompressed using its original

compressor.  Once all pages are removed from an old pool, the pool and its

compressor are freed.

Some of the pages in zswap are same-value filled pages (i.e. contents of the

page have same value or repetitive pattern). These pages include zero-filled

.. kernel-doc:: mm/memremap.c

.. kernel-doc:: mm/hugetlb.c

.. kernel-doc:: mm/swap.c

.. kernel-doc:: mm/zpool.c

.. kernel-doc:: mm/memcontrol.c

.. #kernel-doc:: mm/memory-tiers.c (build warnings)

.. kernel-doc:: mm/shmem.c

  # echo 0 > /sys/module/zswap/parameters/enabled

  # echo 50 > /sys/module/zswap/parameters/max_pool_percent

  # echo deflate-iaa > /sys/module/zswap/parameters/compressor

  # echo zsmalloc > /sys/module/zswap/parameters/zpool

  # echo 1 > /sys/module/zswap/parameters/enabled

  # echo 100 > /proc/sys/vm/swappiness

  # echo never > /sys/kernel/mm/transparent_hugepage/enabled

  echo 0 > /sys/module/zswap/parameters/enabled

  echo 50 > /sys/module/zswap/parameters/max_pool_percent

  echo deflate-iaa > /sys/module/zswap/parameters/compressor

  echo zsmalloc > /sys/module/zswap/parameters/zpool

  echo 1 > /sys/module/zswap/parameters/enabled

  echo 100 > /proc/sys/vm/swappiness

L:	linux-mm@kvack.org

S:	Maintained

F:	Documentation/admin-guide/mm/zswap.rst

F:	include/linux/zpool.h

F:	include/linux/zswap.h

F:	mm/zpool.c

F:	mm/zswap.c

F:	tools/testing/selftests/cgroup/test_zswap.c

CONFIG_IOSCHED_BFQ=y

CONFIG_BFQ_GROUP_IOSCHED=y

CONFIG_BINFMT_MISC=m

CONFIG_ZPOOL=y

CONFIG_ZSWAP=y

CONFIG_ZSWAP_COMPRESSOR_DEFAULT_ZSTD=y

CONFIG_ZSMALLOC=y