Question & Answer
Question
Why is the available memory reported in graph "
Answer
The available memory reported by LSF is the sum of free, buffers and cached from 'free' command.
Some of the memory in the system is used for disk cache, i.e. memory temporarily used by operating system to speed up data access by keeping data in memory and therefore avoiding reads from disk every time. That memory will be made available to an application if the reported free memory runs out. That is why memory reserved by disk cache is also counted for free memory by LSF.
For example,
# free -m
total used free shared buffers cached
Mem: 3961 3719 241 0 163 256
-/+ buffers/cache: 3300 661
Swap: 2047 1 2046
The actual free memory available to a system = (total memory - inuse memory), where inuse memory = (memory reported as used - (buffers + cached)). i.e. 3961 - (3716 - (163+256)) = 661M
Similar value is reported by lsload command of LSF.
# lsload
HOST_NAME status r15s r1m r15m ut pg ls it tmp swp mem
hostname-1. ok 0.4 0.3 0.6 5% 0.0 1 2 12G 1.9G 644M
Note: Above values reported by lsload, free, and "Cur:" in graph are similar, but not identical because it depends on the time of collection.
Also whether a system starts swapping even before free memory runs out depends on vm.swappiness. If it is not 0, a system may start swapping even before free memory runs out.
# sysctl vm.swappiness # (to display current value)
# sysctl -w vm.swappiness=0 # only use swap when we're actually out of available RAM
[{"Product":{"code":"SSZT2D","label":"IBM Spectrum LSF RTM"},"Business Unit":{"code":"BU059","label":"IBM Software w\/o TPS"},"Component":"Not Applicable","Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"10.1","Edition":"","Line of Business":{"code":"LOB10","label":"Data and AI"}},{"Product":{"code":"SSVMSD","label":"Platform RTM"},"Business Unit":{"code":"BU054","label":"Systems w\/TPS"},"Component":"Graphs","Platform":[{"code":"PF025","label":"Platform Independent"}],"Version":"Version Independent","Edition":"","Line of Business":{"code":"","label":""}}]
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Document Information
Modified date:
30 August 2019
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isg3T1024865