Hey,

while the node_reg_mem_percent parameter sounds interesting, it would only be feasible for us on a per job basis (I wasn't able to find it there at first glance). Many of our users need a certain amount of RAM and jobs would fail if they have less. Therefore, this doesn't solve our issue.

Best regards,
Xaver

On 8/14/25 10:42, Guillaume COCHARD via slurm-users wrote:
Hello,

You might want to use the node_reg_mem_percent parameter ( https://slurm.schedmd.com/slurm.conf.html#OPT_node_reg_mem_percent ). For example, if set to 80, it will allow a node to work even if it has only 80% of the declared memory.

Guillaume

De: "Xaver Stiensmeier via slurm-users" <slurm-users@lists.schedmd.com>
À: slurm-users@lists.schedmd.com
Envoyé: Jeudi 14 Août 2025 10:01:26
Objet: [slurm-users] Nodes Become Invalid Due to Less Total RAM Than Expected

Dear slurm-user list,

in the past we had a bigger buffer between RealMemory and the instance memory. We then discovered that the right way is to activating the memory option (SelectTypeParameters=CR_Core_Memory) and setting MemSpecLimit to secure RAM for system processes.

However, now we run into the problem that due to on demand scheduling, we have to setup the slurm.conf in advance by using the RAM values from our flavors as reported by our cloud provider (OpenStack). These RAM values are higher than the RAM values the machines actually have later on:

ram_in_mib by openstack
 total_ram_in_mib by top/slurm
2048 1968
16384 15991
32768 32093
65536 64297
122880 120749
245760 241608
491520 483528

Given that we have to define the slurm.conf in advance, we kinda have to predict how much total ram the instances have once created. Of course I used linear regression to approximate the total ram and then lowered it a bit to have some cushion, but this feels unsafe given that future flavors could differ from that.

From the kernel documentation I know that MemTotal is

MemTotal: Total usable ram (i.e. physical ram minus a few reserved bits and the kernel binary code)

but given that the concrete reserved bits are quite complex, I am wondering whether I am doing something wrong as this issue doesn't feel niche enough to be that complicated.

---

Anyway, setting the RAM value in the slurm.conf above total ram by predicting too much, leads to errors and nodes being marked as invalid:

[2025-08-11T08:19:04.736] debug:  Node NODE_NAME has low real_memory size (241607 / 245760) < 100.00%
[2025-08-11T08:19:04.736] error: _slurm_rpc_node_registration node=NODE_NAME: Invalid argument

or

[2025-07-03T12:57:18.486] error: Setting node NODE_NAME state to INVAL with reason:Low RealMemory (reported:64295 < 100.00% of configured:68719)

Any hint on how to solve this is much appreciated!

Best regards,
Xaver

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