revert documentaion update for memcg's dirty ratio.

Subjct: Revert memory cgroup dirty_ratio Documentation.

The commit ece72400c2 adds documentation
for memcg's dirty ratio. But the function is not implemented yet.
Remove the documentation for avoiding confusing users.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Reviewed-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/cgroups/memory.txt

@@ -385,10 +385,6 @@ mapped_file	- # of bytes of mapped file (includes tmpfs/shmem)
 pgpgin		- # of pages paged in (equivalent to # of charging events).
 pgpgout		- # of pages paged out (equivalent to # of uncharging events).
 swap		- # of bytes of swap usage
-dirty		- # of bytes that are waiting to get written back to the disk.
-writeback	- # of bytes that are actively being written back to the disk.
-nfs_unstable	- # of bytes sent to the NFS server, but not yet committed to
-		the actual storage.
 inactive_anon	- # of bytes of anonymous memory and swap cache memory on
 		LRU list.
 active_anon	- # of bytes of anonymous and swap cache memory on active
@@ -410,9 +406,6 @@ total_mapped_file	- sum of all children's "cache"
 total_pgpgin		- sum of all children's "pgpgin"
 total_pgpgout		- sum of all children's "pgpgout"
 total_swap		- sum of all children's "swap"
-total_dirty		- sum of all children's "dirty"
-total_writeback		- sum of all children's "writeback"
-total_nfs_unstable	- sum of all children's "nfs_unstable"
 total_inactive_anon	- sum of all children's "inactive_anon"
 total_active_anon	- sum of all children's "active_anon"
 total_inactive_file	- sum of all children's "inactive_file"
@@ -460,73 +453,6 @@ memory under it will be reclaimed.
 You can reset failcnt by writing 0 to failcnt file.
 # echo 0 > .../memory.failcnt
 
-5.5 dirty memory
-
-Control the maximum amount of dirty pages a cgroup can have at any given time.
-
-Limiting dirty memory is like fixing the max amount of dirty (hard to reclaim)
-page cache used by a cgroup.  So, in case of multiple cgroup writers, they will
-not be able to consume more than their designated share of dirty pages and will
-be forced to perform write-out if they cross that limit.
-
-The interface is equivalent to the procfs interface: /proc/sys/vm/dirty_*.  It
-is possible to configure a limit to trigger both a direct writeback or a
-background writeback performed by per-bdi flusher threads.  The root cgroup
-memory.dirty_* control files are read-only and match the contents of
-the /proc/sys/vm/dirty_* files.
-
-Per-cgroup dirty limits can be set using the following files in the cgroupfs:
-
-- memory.dirty_ratio: the amount of dirty memory (expressed as a percentage of
-  cgroup memory) at which a process generating dirty pages will itself start
-  writing out dirty data.
-
-- memory.dirty_limit_in_bytes: the amount of dirty memory (expressed in bytes)
-  in the cgroup at which a process generating dirty pages will start itself
-  writing out dirty data.  Suffix (k, K, m, M, g, or G) can be used to indicate
-  that value is kilo, mega or gigabytes.
-
-  Note: memory.dirty_limit_in_bytes is the counterpart of memory.dirty_ratio.
-  Only one of them may be specified at a time.  When one is written it is
-  immediately taken into account to evaluate the dirty memory limits and the
-  other appears as 0 when read.
-
-- memory.dirty_background_ratio: the amount of dirty memory of the cgroup
-  (expressed as a percentage of cgroup memory) at which background writeback
-  kernel threads will start writing out dirty data.
-
-- memory.dirty_background_limit_in_bytes: the amount of dirty memory (expressed
-  in bytes) in the cgroup at which background writeback kernel threads will
-  start writing out dirty data.  Suffix (k, K, m, M, g, or G) can be used to
-  indicate that value is kilo, mega or gigabytes.
-
-  Note: memory.dirty_background_limit_in_bytes is the counterpart of
-  memory.dirty_background_ratio.  Only one of them may be specified at a time.
-  When one is written it is immediately taken into account to evaluate the dirty
-  memory limits and the other appears as 0 when read.
-
-A cgroup may contain more dirty memory than its dirty limit.  This is possible
-because of the principle that the first cgroup to touch a page is charged for
-it.  Subsequent page counting events (dirty, writeback, nfs_unstable) are also
-counted to the originally charged cgroup.
-
-Example: If page is allocated by a cgroup A task, then the page is charged to
-cgroup A.  If the page is later dirtied by a task in cgroup B, then the cgroup A
-dirty count will be incremented.  If cgroup A is over its dirty limit but cgroup
-B is not, then dirtying a cgroup A page from a cgroup B task may push cgroup A
-over its dirty limit without throttling the dirtying cgroup B task.
-
-When use_hierarchy=0, each cgroup has dirty memory usage and limits.
-System-wide dirty limits are also consulted.  Dirty memory consumption is
-checked against both system-wide and per-cgroup dirty limits.
-
-The current implementation does not enforce per-cgroup dirty limits when
-use_hierarchy=1.  System-wide dirty limits are used for processes in such
-cgroups.  Attempts to read memory.dirty_* files return the system-wide
-values.  Writes to the memory.dirty_* files return error.  An enhanced
-implementation is needed to check the chain of parents to ensure that no
-dirty limit is exceeded.
-
 6. Hierarchy support
 
 The memory controller supports a deep hierarchy and hierarchical accounting.