technical:slurm:node-memory-sizes

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technical:slurm:node-memory-sizes [2019-02-18 12:15] – [Proposed RealMemory sizes] freytechnical:slurm:node-memory-sizes [2019-02-18 12:32] – [Requesting specific node types] frey
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 The changes did not need to be rolled-back, since an additional mode (//FastSchedule=2//) instructs Slurm to ignore such disparity.  Thus, the v1.1.3 changes went into production in that mode circa 10:00. The changes did not need to be rolled-back, since an additional mode (//FastSchedule=2//) instructs Slurm to ignore such disparity.  Thus, the v1.1.3 changes went into production in that mode circa 10:00.
  
-One additional problem could present itself under the v1.1.3 use of nominal physical memory size for the nodes  Consider the following:+One additional problem could present itself under the v1.1.3 use of nominal physical memory size for the nodes.  Consider the following:
  
   * A node runs a job requesting 28 cores and 100 GiB of memory, leaving 8 cores and 28 GiB of memory available according to the node configuration.   * A node runs a job requesting 28 cores and 100 GiB of memory, leaving 8 cores and 28 GiB of memory available according to the node configuration.
-  * A second job from a different user, requesting 4 cores and 28 GiB of memory, is scheduled on the node.+  * The same node runs a second job that requests 4 cores and 28 GiB of memory.
  
-Since the OS itself occupies some non-trivial amount of the physical memory, the second job eventually extends memory usage above and beyond the amount of physical memory present.  This causes memory usage to spill into swap space, slowing all jobs on the node.+Since the OS itself occupies some non-trivial amount of the physical memory, the second job eventually extends memory usage above and beyond the amount of physical memory present in the node.  This causes memory usage to spill into swap space, slowing all jobs on the node considerably.
  
 <WRAP negative round> <WRAP negative round>
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 A workgroup QOS which under v1.1.3 had ''cpu=756,mem=3801088'' reflecting (13) //Gen1/128 GiB// nodes and (8) //Gen1/256 GiB// nodes will change to ''cpu=756,mem=3698688'' to reflect the RealMemory sizes specified above. A workgroup QOS which under v1.1.3 had ''cpu=756,mem=3801088'' reflecting (13) //Gen1/128 GiB// nodes and (8) //Gen1/256 GiB// nodes will change to ''cpu=756,mem=3698688'' to reflect the RealMemory sizes specified above.
 +
 +==== Requesting specific node types ====
 +
 +Our Slurm has always defined several //features// on each node in the cluster:
 +
 +<code bash>
 +$ scontrol show node r00n00 
 +NodeName=r00n00 Arch=x86_64 CoresPerSocket=36
 +   CPUAlloc=0 CPUErr=0 CPUTot=72 CPULoad=0.07
 +   AvailableFeatures=E5-2695,E5-2695v4,128GB,HT
 +   ActiveFeatures=E5-2695,E5-2695v4,128GB,HT
 +      :
 +</code>
 +
 +It is possible to constrain a job to execute on a node with a specific nominal memory size using these features:
 +
 +<code bash>
 +$ sbatch … --constraint=128GB …
 +$ sbatch … --constraint=256GB …
 +$ sbatch … --constraint=512GB …
 +</code>
 +
 +The other features reflect the model processor present in the node.  All Gen1 nodes use the Intel ''E5-2695v4''; node ''r00n00'' is part of the ''devel'' partition and has hyperthreading enabled, hence the ''HT'' feature.
 ===== Implementation ===== ===== Implementation =====