cgroups: Update cgroup.conf manpage

Update cgroup.conf(5) with documentation for new parameters
CgroupMountpoint, MinRAMSpace, MaxRAMPercent and MaxSwapPercent.
Also include information about handling of AllowedRAMSpace when
memory is not explicitly allocated by SLURM.

doc/man/man5/cgroup.conf.5

@@ -25,6 +25,12 @@ one is a proctrack plugin, the second one a task plugin.
 The following cgroup.conf parameters are defined to control the general behavior
 of Slurm cgroup plugins.
 
+.TP
+.BICgroupMountpoint " PATH"
+Specify the \fIPATH\fR under which cgroups should be mounted. This
+should be a writeable directory which will contain cgroups mounted
+one per subsystem. The default \fIPATH\fR is /cgroup.
+
 .TP
 \fBCgroupAutomount\fR=<yes|no>
 Slurm cgroup plugins require valid and functional cgroup subsystem to be mounted
@@ -105,17 +111,19 @@ would be added :
 .TP
 \fBAllowedRAMSpace\fR=<number>
 Constrain the job cgroup RAM to this percentage of the allocated memory.
-The default value is 100.
-If the limit is exceeded, the job steps will be killed and a warning message
-will be written to standard error.
-Also see \fBConstrainRAMSpace\fR.
+The default value is 100. If SLURM is not allocating memory to jobs,
+The percentage supplied may be expressed as floating point
+number, e.g. 98.5. If the \fBAllowedRAMSpace\fR limit is exceeded, the
+job steps will be killed and a warning message will be written to standard
+error.  Also see \fBConstrainRAMSpace\fR.
 
 .TP
 \fBAllowedSwapSpace\fR=<number>
-Constrain the job cgroup swap space to this percentage of the allocated memory.
-The default value is 0.
-If the limit is exceeded, the job steps will be killed and a warning message
-will be written to standard error.
+Constrain the job cgroup swap space to this percentage of the allocated
+memory.  The default value is 0, which means that RAM+Swap will be limited
+to \fBAllowedRAMSpace\fR. The supplied percentage may be expressed as a
+floating point number, e.g. 50.5.  If the limit is exceeded, the job steps
+will be killed and a warning message will be written to standard error.
 Also see \fBConstrainSwapSpace\fR.
 
 .TP
@@ -130,6 +138,28 @@ If configured to "yes" then constrain the job's swap space usage.
 The default value is "no".
 Also see \fBAllowedSwapSpace\fR.
 
+.TP
+\fBMaxRAMPercent\fR=\fIPERCENT\fR
+Set an upper bound in percent of total RAM on the RAM constraint for a job.
+This will be the memory constraint applied to jobs that are not explicitly
+allocated memory by SLURM. The \fIPERCENT\fR may be an arbitrary floating
+point number. The default value is 100.
+
+.TP
+\fBMaxSwapPercent\fR=\fIPERCENT\fR
+Set an upper bound (in percent of total RAM) on the amount of RAM+Swap
+that may be used for a job. This will be the swap limit applied to jobs
+on systems where memory is not being explicitly allocated to job. The
+\fIPERCENT\fR may be an arbitrary floating point number between 0 and 100.
+The default value is 100.
+
+.TP
+\fBMinRAMSpace\fR=<number>
+Set a lower bound (in MB) on the memory limits defined by
+\fBAllowedRAMSpace\fR and \fBAllowedSwapSpace\fR. This prevents
+accidentally creating a memory cgroup with such a low limit that slurmstepd
+is immediately killed due to lack of RAM. The default limit is 30M.
+
 .TP
 \fBConstrainDevices\fR=<yes|no>
 If configured to "yes" then constrain the job's allowed devices based on GRES