zswap: add to mm/

zswap: add to mm/

zswap is a thin backend for frontswap that takes pages that are in the
process of being swapped out and attempts to compress them and store
them in a RAM-based memory pool.  This can result in a significant I/O
reduction on the swap device and, in the case where decompressing from
RAM is faster than reading from the swap device, can also improve
workload performance.

It also has support for evicting swap pages that are currently
compressed in zswap to the swap device on an LRU(ish) basis.  This
functionality makes zswap a true cache in that, once the cache is full,
the oldest pages can be moved out of zswap to the swap device so newer
pages can be compressed and stored in zswap.

This patch adds the zswap driver to mm/

Signed-off-by: Seth Jennings <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Nitin Gupta <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Dan Magenheimer <[email protected]>
Cc: Robert Jennings <[email protected]>
Cc: Jenifer Hopper <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Larry Woodman <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Joe Perches <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Cody P Schafer <[email protected]>
Cc: Hugh Dickens <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Fengguang Wu <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>