[Condor-users] RAM allocated to dynamic slots

[Brian Candler <B.Candler@xxxxxxxxx>]

I wonder if someone can explain the following to me.  I am just getting
started with partitioned slots, but I find that if I submit jobs with
RequestMemory = 1991 then the apparent memory allocated for the slot is 2688
(which is 35% higher than I requested)

$ condor_status

Name               OpSys      Arch   State     Activity LoadAv Mem   ActvtyTime

slot1@dev-storage1 LINUX      X86_64 Unclaimed Idle     1.000  1792  0+00:04:42
slot1_1@dev-storag LINUX      X86_64 Claimed   Busy     1.010  2688  0+00:03:00
slot1_2@dev-storag LINUX      X86_64 Claimed   Suspende 1.910  2688  0+00:00:04
slot1@dev-storage2 LINUX      X86_64 Unclaimed Idle     1.000  1792  0+00:04:42
slot1_1@dev-storag LINUX      X86_64 Claimed   Busy     0.940  2688  0+00:03:31
slot1_2@dev-storag LINUX      X86_64 Claimed   Busy     1.440  2688  0+00:03:29
                     Total Owner Claimed Unclaimed Matched Preempting Backfill
        X86_64/LINUX     6     0       4         2       0          0        0
               Total     6     0       4         2       0          0        0

The slots are defined as follows in /home/condor/condor_config.local:

# On dev-storage1: a 2-core CPU with hyperthreading, 8GB RAM
SLOT_TYPE_1 = cpus=2, ram=90%, swap=100%, disk=100%
SLOT_TYPE_1_PARTITIONABLE = True
NUM_SLOTS_TYPE_1 = 1

# On dev-storage2: a 4-core CPU without hyperthreading, 8GB RAM
SLOT_TYPE_1 = cpus=4, ram=90%, swap=100%, disk=100%
SLOT_TYPE_1_PARTITIONABLE = True
NUM_SLOTS_TYPE_1 = 1

Now, if I retry with the job having RequestMemory = 750 I get an apparent
Mem used in the dynamic slot of 896, which is only a 20% premium. 
condor_status -long also shows Memory=896 and TotalSlotMemory=896 for the
used dynamic slots.

Is Condor over-estimating the declared memory usage on purpose? If so, where
can I look to tweak this down a bit?

Thanks,

Brian.

P.S. In the partitionable slots I see
  TotalMemory = 7965
  TotalSlotMemory = 7168
which correctly reflects the "ram=90%" for the slot.