[Beowulf] [OOM killer/scheduler] disabling swap on cluster nodes?

[Greg Keller]

Any time you touch swap you need to consider both
overcommit_memory
AND
overcommit_ratio

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
near 100.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.beowulf.org/pipermail/beowulf/attachments/20150209/f6e75c4b/attachment.html>