[Beowulf] [OOM killer/scheduler] disabling swap on cluster nodes?
Greg at Keller.net
Mon Feb 9 12:28:29 PST 2015
Any time you touch swap you need to consider both
The "Ratio" is 50% by default, and the math was counter-intuitive to me...
overcommit_memory set to Option 2 tells the kernel it is not permitted to
exceed swap + a configurable amount (default is 50%) of physical RAM.
So with Swap Set to 8 GB in a 128GB host the math would be...
Swap (8GB) + Ram @ 50% (64GB) = 72GB Max Committed by the kernel = bad
So disabling swap means....
Ram @ 50% (64GB) = worse!
Moral of the story is, either set swap to be at least 50% of RAM or the
Kernel will not use commit all the RAM it has with the default configs.
For Diskless & Swapless we set overcommit_memory to 2 and overcommit_ratio
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