Merge branch 'akpm' (patches from Andrew)

Merge third patch-bomb from Andrew Morton:

 - even more of the rest of MM

 - lib/ updates

 - checkpatch updates

 - small changes to a few scruffy filesystems

 - kmod fixes/cleanups

 - kexec updates

 - a dma-mapping cleanup series from hch

* emailed patches from Andrew Morton <akpm@linux-foundation.org>: (81 commits)
  dma-mapping: consolidate dma_set_mask
  dma-mapping: consolidate dma_supported
  dma-mapping: cosolidate dma_mapping_error
  dma-mapping: consolidate dma_{alloc,free}_noncoherent
  dma-mapping: consolidate dma_{alloc,free}_{attrs,coherent}
  mm: use vma_is_anonymous() in create_huge_pmd() and wp_huge_pmd()
  mm: make sure all file VMAs have ->vm_ops set
  mm, mpx: add "vm_flags_t vm_flags" arg to do_mmap_pgoff()
  mm: mark most vm_operations_struct const
  namei: fix warning while make xmldocs caused by namei.c
  ipc: convert invalid scenarios to use WARN_ON
  zlib_deflate/deftree: remove bi_reverse()
  lib/decompress_unlzma: Do a NULL check for pointer
  lib/decompressors: use real out buf size for gunzip with kernel
  fs/affs: make root lookup from blkdev logical size
  sysctl: fix int -> unsigned long assignments in INT_MIN case
  kexec: export KERNEL_IMAGE_SIZE to vmcoreinfo
  kexec: align crash_notes allocation to make it be inside one physical page
  kexec: remove unnecessary test in kimage_alloc_crash_control_pages()
  kexec: split kexec_load syscall from kexec core code
  ...

1 files changed, 28 insertions, 8 deletions

diff --git a/Documentation/vm/zswap.txt b/Documentation/vm/zswap.txt
index 8458c0861e4e..89fff7d611cc 100644
--- a/Documentation/vm/zswap.txt
+++ b/Documentation/vm/zswap.txt
@@ -32,7 +32,7 @@ can also be enabled and disabled at runtime using the sysfs interface.
 An example command to enable zswap at runtime, assuming sysfs is mounted
 at /sys, is:
 
-echo 1 > /sys/modules/zswap/parameters/enabled
+echo 1 > /sys/module/zswap/parameters/enabled
 
 When zswap is disabled at runtime it will stop storing pages that are
 being swapped out.  However, it will _not_ immediately write out or fault
@@ -49,14 +49,26 @@ Zswap receives pages for compression through the Frontswap API and is able to
 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 zbud for the managing the compressed memory pool.  Each
-allocation in zbud is not directly accessible by address.  Rather, a handle is
+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
 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.
+pages are freed.  The pool is not preallocated.  By default, a zpool of type
+zbud is created, but it can be selected at boot time by setting the "zpool"
+attribute, e.g. zswap.zpool=zbud.  It can also be changed at runtime using the
+sysfs "zpool" attribute, e.g.
+
+echo zbud > /sys/module/zswap/parameters/zpool
+
+The zbud type zpool allocates exactly 1 page to store 2 compressed pages, which
+means the compression ratio will always be 2:1 or worse (because of half-full
+zbud pages).  The zsmalloc type zpool has a more complex compressed page
+storage method, and it can achieve greater storage densities.  However,
+zsmalloc does not implement compressed page eviction, so once zswap fills it
+cannot evict the oldest page, it can only reject new pages.
 
 When a swap page is passed from frontswap to zswap, zswap maintains a mapping
-of the swap entry, a combination of the swap type and swap offset, to the zbud
+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.
@@ -74,9 +86,17 @@ controlled policy:
 * max_pool_percent - The maximum percentage of memory that the compressed
     pool can occupy.
 
-Zswap allows the compressor to be selected at kernel boot time by setting the
-“compressor” attribute.  The default compressor is lzo.  e.g.
-zswap.compressor=deflate
+The default compressor is lzo, but it can be selected at boot time by setting
+the “compressor” attribute, e.g. zswap.compressor=lzo.  It can also be changed
+at runtime using the sysfs "compressor" attribute, e.g.
+
+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.
 
 A debugfs interface is provided for various statistic about pool size, number
 of pages stored, and various counters for the reasons pages are rejected.