[Devel] [PATCH 02/10] memcg: document cgroup dirty memory interfaces

[Greg Thelen]

Document cgroup dirty memory interfaces and statistics.

Signed-off-by: Andrea Righi <arighi at develer.com>
Signed-off-by: Greg Thelen <gthelen at google.com>
---
 Documentation/cgroups/memory.txt |   37 +++++++++++++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
index 7781857..eab65e2 100644
--- a/Documentation/cgroups/memory.txt
+++ b/Documentation/cgroups/memory.txt
@@ -385,6 +385,10 @@ 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		- # 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
@@ -453,6 +457,39 @@ 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_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.
+
+- 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_bytes: the amount of dirty memory (expressed in bytes)
+  in the cgroup at which background writeback kernel threads will start writing
+  out dirty data.
+
 6. Hierarchy support
 
 The memory controller supports a deep hierarchy and hierarchical accounting.
-- 
1.7.1

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