Cannot enforce memory limits in SLURM

I am using Slurm on a single node (control and compute) and I cannot seem to correctly limit memory. The script seems to call SBATCH with small memory values (3G), but I see values in top that exceed 25G. Sacct gives me the correct values:

squeue -o "%C %m"
CPUS MIN_MEMORY
2 3G

This is my slurm.conf:

#
SlurmctldHost=schopenhauer
#
#DisableRootJobs=NO
#EnforcePartLimits=NO
#Epilog=
#EpilogSlurmctld=
#FirstJobId=1
#MaxJobId=999999
#GresTypes=
#GroupUpdateForce=0
#GroupUpdateTime=600
#JobFileAppend=0
#JobRequeue=1
#JobSubmitPlugins=1
#KillOnBadExit=0
#LaunchType=launch/slurm
#Licenses=foo*4,bar
#MailProg=/bin/mail
#MaxJobCount=5000
#MaxStepCount=40000
#MaxTasksPerNode=128
MpiDefault=none
#MpiParams=ports=#-#
#PluginDir=
#PlugStackConfig=
#PrivateData=jobs
#ProctrackType=proctrack/cgroup
ProctrackType=proctrack/linuxproc
#Prolog=
#PrologFlags=
#PrologSlurmctld=
#PropagatePrioProcess=0
#PropagateResourceLimits=
#PropagateResourceLimitsExcept=
#RebootProgram=
ReturnToService=1
#SallocDefaultCommand=
SlurmctldPidFile=/var/run/slurmctld.pid
SlurmctldPort=6817
SlurmdPidFile=/var/run/slurmd.pid
SlurmdPort=6818
SlurmdSpoolDir=/var/spool/slurmd
SlurmUser=slurm
#SlurmdUser=root
#SrunEpilog=
#SrunProlog=
StateSaveLocation=/var/spool/slurmd
SwitchType=switch/none
#TaskEpilog=
TaskPlugin=task/affinity
TaskPluginParam=Sched
#TaskProlog=
#TopologyPlugin=topology/tree
#TmpFS=/tmp
#TrackWCKey=no
#TreeWidth=
#UnkillableStepProgram=
#UsePAM=0
#
#
# TIMERS
#BatchStartTimeout=10
#CompleteWait=0
#EpilogMsgTime=2000
#GetEnvTimeout=2
#HealthCheckInterval=0
#HealthCheckProgram=
InactiveLimit=0
KillWait=30
#MessageTimeout=10
#ResvOverRun=0
MinJobAge=300000
#OverTimeLimit=0
SlurmctldTimeout=120
SlurmdTimeout=300
#UnkillableStepTimeout=60
#VSizeFactor=0
Waittime=0
#
#
# SCHEDULING
#DefMemPerCPU=0
#MaxMemPerCPU=0
#SchedulerTimeSlice=30
SchedulerType=sched/backfill
SelectType=select/cons_tres
SelectTypeParameters=CR_Core
#
#
# JOB PRIORITY
#PriorityFlags=
#PriorityType=priority/basic
#PriorityDecayHalfLife=
#PriorityCalcPeriod=
#PriorityFavorSmall=
#PriorityMaxAge=
#PriorityUsageResetPeriod=
#PriorityWeightAge=
#PriorityWeightFairshare=
#PriorityWeightJobSize=
#PriorityWeightPartition=
#PriorityWeightQOS=
#
#
# LOGGING AND ACCOUNTING
#AccountingStorageEnforce=0
#AccountingStorageHost=
AccountingStorageLoc=/var/log/slurm/slurm_jobacct.log
#AccountingStoragePass=
#AccountingStoragePort=
AccountingStorageType=accounting_storage/filetxt
#AccountingStorageUser=
AccountingStoreJobComment=YES
ClusterName=cluster
#DebugFlags=
#JobCompHost=
JobCompLoc=/var/log/slurm/slurm_jobcomp.log
#JobCompPass=
#JobCompPort=
JobCompType=jobcomp/filetxt
#JobCompUser=
#JobContainerType=job_container/none
JobAcctGatherFrequency=30
JobAcctGatherType=jobacct_gather/linux
SlurmctldDebug=info
SlurmctldLogFile=/var/log/slurm/slurmctld.log
SlurmdDebug=debug5
SlurmdLogFile=/var/log/slurm/slurmd.log
#SlurmSchedLogFile=
#SlurmSchedLogLevel=
#
#
# POWER SAVE SUPPORT FOR IDLE NODES (optional)
#SuspendProgram=
#ResumeProgram=
#SuspendTimeout=
#ResumeTimeout=
#ResumeRate=
#SuspendExcNodes=
#SuspendExcParts=
#SuspendRate=
#SuspendTime=
#
#
# COMPUTE NODES
NodeName=schopenhauer CPUs=128 Boards=1 SocketsPerBoard=2 CoresPerSocket=32 ThreadsPerCore=2 RealMemory=500000 State=UNKNOWN
PartitionName=short Nodes=schopenhauer Default=YES MaxTime=INFINITE State=UP

Did I misunderstand something? Why does it say minimum memory when I want to make that minimum and maximum as well?

EDIT: I just noticed by setting required memory to a larger one that this doesn't work as a minimum either i.e. many tasks were started even though there was enough RAM for only 12 of them (I requested 40G and I have 500G). Is this the same problem?

Solution

Slurm controls memory through the Linux cgroup functionality. You need to set TaskPlugin=task/cgroup in slurm.conf (Cf. https://slurm.schedmd.com/cgroups.html) and ConstrainRAMSpace=yes in cgroup.conf (Cf. https://slurm.schedmd.com/cgroup.conf.html). Then the memory requested by jobs with --mem or --mem-per-cpu becomes effectively a hard limit in addition to being a resource request.

The -m option of gives the memory requested by the job. As a request, it is considered a minimum requirement. But if you configure cgroup it effectively also becomes the maximum.