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    • Seth Jennings's avatar
      zbud: add to mm/ · 4e2e2770
      Seth Jennings authored
      zbud is an special purpose allocator for storing compressed pages.  It
      is designed to store up to two compressed pages per physical page.
      While this design limits storage density, it has simple and
      deterministic reclaim properties that make it preferable to a higher
      density approach when reclaim will be used.
      
      zbud works by storing compressed pages, or "zpages", together in pairs
      in a single memory page called a "zbud page".  The first buddy is "left
      justifed" at the beginning of the zbud page, and the last buddy is
      "right justified" at the end of the zbud page.  The benefit is that if
      either buddy is freed, the freed buddy space, coalesced with whatever
      slack space that existed between the buddies, results in the largest
      possible free region within the zbud page.
      
      zbud also provides an attractive lower bound on density.  The ratio of
      zpages to zbud pages can not be less than 1.  This ensures that zbud can
      never "do harm" by using more pages to store zpages than the
      uncompressed zpages would have used on their own.
      
      This implementation is a rewrite of the zbud allocator internally used
      by zcache in the driver/staging tree.  The rewrite was necessary to
      remove some of the zcache specific elements that were ingrained
      throughout and provide a generic allocation interface that can later be
      used by zsmalloc and others.
      
      This patch adds zbud to mm/ for later use by zswap.
      Signed-off-by: default avatarSeth Jennings <sjenning@linux.vnet.ibm.com>
      Acked-by: default avatarRik van Riel <riel@redhat.com>
      Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
      Cc: Nitin Gupta <ngupta@vflare.org>
      Cc: Minchan Kim <minchan@kernel.org>
      Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
      Cc: Dan Magenheimer <dan.magenheimer@oracle.com>
      Cc: Robert Jennings <rcj@linux.vnet.ibm.com>
      Cc: Jenifer Hopper <jhopper@us.ibm.com>
      Cc: Mel Gorman <mgorman@suse.de>
      Cc: Johannes Weiner <jweiner@redhat.com>
      Cc: Larry Woodman <lwoodman@redhat.com>
      Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
      Cc: Dave Hansen <dave@sr71.net>
      Cc: Joe Perches <joe@perches.com>
      Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
      Cc: Cody P Schafer <cody@linux.vnet.ibm.com>
      Cc: Hugh Dickens <hughd@google.com>
      Cc: Paul Mackerras <paulus@samba.org>
      Cc: Bob Liu <bob.liu@oracle.com>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      4e2e2770