staging: zsmalloc: add gfp flags to zs_create_pool

zs_create_pool() currently takes a gfp flags argument
that is used when growing the memory pool.  However
it is not used in allocating the metadata for the pool
itself.  That is currently hardcoded to GFP_KERNEL.

zswap calls zs_create_pool() at swapon time which is done
in atomic context, resulting in a "might sleep" warning.

This patch changes the meaning of the flags argument in
zs_create_pool() to mean the flags for the metadata allocation,
and adds a flags argument to zs_malloc that will be used for
memory pool growth if required.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
staging: zsmalloc: remove unsed pool name

zs_create_pool() currently takes a name argument which is
never used in any useful way.

This patch removes it.

Signed-off-by: Seth Jennnings <sjenning@linux.vnet.ibm.com>
staging: zsmalloc: add page alloc/free callbacks

This patch allows users of zsmalloc to register the
allocation and free routines used by zsmalloc to obtain
more pages for the memory pool.  This allows the user
more control over zsmalloc pool policy and behavior.

If the user does not wish to control this, alloc_page() and
__free_page() are used by default.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
staging: zsmalloc: make CLASS_DELTA relative to PAGE_SIZE

Right now ZS_SIZE_CLASS_DELTA is hardcoded to be 16.  This
creates 254 classes for systems with 4k pages. However, on
PPC64 with 64k pages, it creates 4095 classes which is far
too many.

This patch makes ZS_SIZE_CLASS_DELTA relative to PAGE_SIZE
so that regardless of the page size, there will be the same
number of classes.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
debugfs: add get/set for atomic types

debugfs currently lack the ability to create attributes
that set/get atomic_t values.

This patch adds support for this through a new
debugfs_create_atomic_t() function.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
zsmalloc: promote to lib/

This patch promotes the slab-based zsmalloc memory allocator
from the staging tree to lib/

zswap depends on this allocator for storing compressed RAM pages
in an efficient way under system wide memory pressure where
high-order (greater than 0) page allocation are very likely to
fail.

For more information on zsmalloc and its internals, read the
documentation at the top of the zsmalloc.c file.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
--
This patch is similar to a patch Minchan has on out on the list
to promote for use in zram.
mm: break up swap_writepage() for frontswap backends

swap_writepage() is currently where frontswap hooks into the swap
write path to capture pages with the frontswap_store() function.
However, if a frontswap backend wants to "resume" the writeback of
a page to the swap device, it can't call swap_writepage() as
the page will simply reenter the backend.

This patch separates swap_writepage() into a top and bottom half, the
bottom half named __swap_writepage() to allow a frontswap backend,
like zswap, to resume writeback beyond the frontswap_store() hook and
by notified when the writeback completes.

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
zswap: add to mm/

zswap is a thin compression backend for frontswap. It receives
pages from frontswap and attempts to store them in a compressed
memory pool, resulting in an effective partial memory reclaim and
dramatically reduced swap device I/O.

Additional, in most cases, pages can be retrieved from this
compressed store much more quickly than reading from tradition
swap devices resulting in faster performance for many workloads.

This patch adds the zswap driver to mm/

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
zswap: add documentation

This patch adds the documentation file for the zswap functionality

Signed-off-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Merge branch '3.7/zswap' into 3.7/master