[PATCH 1/2] doc: cgroup: use graphviz code instead of ASCII art

Otto Sabart
2018-12-30T16:50:04Z

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The graphviz looks better. This patch also fixes multiple build warnings:
"WARNING: Block quote ends without a blank line; unexpected unindent."

Signed-off-by: Otto Sabart <ottosabart@seberm.com>
---
Documentation/admin-guide/cgroup-v2.rst | 83 ++++++++++++++++++++-----
1 file changed, 66 insertions(+), 17 deletions(-)

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index 7bf3f129c68b..80c88a0869e4 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -344,10 +344,21 @@ example, to start a clean-up operation after all processes of a given
sub-hierarchy have exited. The populated state updates and
notifications are recursive. Consider the following sub-hierarchy
where the numbers in the parentheses represent the numbers of processes
-in each cgroup::
+in each cgroup:

- A(4) - B(0) - C(1)
- \ D(0)
+.. kernel-render:: DOT
+ :alt: hierarchy
+
+ digraph subhierarchy {
+ edge [
+ arrowhead="none"
+ ];
+ rankdir=LR;
+
+ "A(4)" -> "B(0)";
+ "B(0)" -> "C(1)";
+ "B(0)" -> "D(0)";
+ }

A, B and C's "populated" fields would be 1 while D's 0. After the one
process in C exits, B and C's "populated" fields would flip to "0" and
@@ -380,10 +391,21 @@ are specified, the last one is effective.
Enabling a controller in a cgroup indicates that the distribution of
the target resource across its immediate children will be controlled.
Consider the following sub-hierarchy. The enabled controllers are
-listed in parentheses::
+listed in parentheses:
+
+.. kernel-render:: DOT
+ :alt: hierarchy

- A(cpu,memory) - B(memory) - C()
- \ D()
+ digraph subhierarchy {
+ edge [
+ arrowhead="none"
+ ];
+ rankdir=LR;
+
+ "A(cpu,memory)" -> "B(memory)";
+ "B(memory)" -> "C()";
+ "B(memory)" -> "D()";
+ }

As A has "cpu" and "memory" enabled, A will control the distribution
of CPU cycles and memory to its children, in this case, B. As B has
@@ -497,12 +519,30 @@ in from or push out to outside the sub-hierarchy.

For an example, let's assume cgroups C0 and C1 have been delegated to
user U0 who created C00, C01 under C0 and C10 under C1 as follows and
-all processes under C0 and C1 belong to U0::
+all processes under C0 and C1 belong to U0:
+
+.. kernel-render:: DOT
+ :alt: cgroup hierarchy

- ~~~~~~~~~~~~~ - C0 - C00
- ~ cgroup ~ \ C01
- ~ hierarchy ~
- ~~~~~~~~~~~~~ - C1 - C10
+ digraph hierarchyc0 {
+ edge [
+ arrowhead="none"
+ ];
+
+ "C0" -> "C00";
+ "C0" -> "C01";
+ }
+
+.. kernel-render:: DOT
+ :alt: cgroup hierarchy
+
+ digraph hierarchyc1 {
+ edge [
+ arrowhead="none"
+ ];
+
+ "C1" -> "C10";
+ }

Let's also say U0 wants to write the PID of a process which is
currently in C10 into "C00/cgroup.procs". U0 has write access to the
@@ -1505,12 +1545,21 @@ The limits are only applied at the peer level in the hierarchy. This means that
in the diagram below, only groups A, B, and C will influence each other, and
groups D and F will influence each other. Group G will influence nobody.

- [root]
- / | \
- A B C
- / \ |
- D F G
-
+.. kernel-render:: DOT
+ :alt: Peer hierarchy
+
+ digraph hierarchy {
+ edge [
+ arrowhead="none"
+ ];
+
+ "[root]" -> "A";
+ "[root]" -> "B";
+ "[root]" -> "C";
+ "A" -> "D";
+ "A" -> "F";
+ "B" -> "G";
+ }

So the ideal way to configure this is to set io.latency in groups A, B, and C.
Generally you do not want to set a value lower than the latency your device
--
2.17.2

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