On Sun, 8 Dec 2019 at 00:53, Martin Verges <martin.verges(a)croit.io> wrote: Given the commentary on this page advocating at least some swap to enable Linux to manage memory when under pressure: https://utcc.utoronto.ca/~cks/space/blog/unix/NoSwapConsequence is it worth modifying the advice to at least have some swap available (even if only say 5% of overall memory)? There was a hnews thread here but to me it seemed inconclusive about solving the overall problem (other than applications taking more responsibility for memory consumption): https://news.ycombinator.com/item?id=20641551

I’ve had one or two situations where swap might have helped a memory consumption problem, but others in which it would have *worsened* cluster performance. Sometimes it’s better for the *cluster* for an OSD to die / restart / get OOMkilled than for it to limp along sluggishly. In the past RAM capacity and cost were such that one had to compromise on the amount provisioned, today with a Ceph cluster if one can’t get CapEx to properly outfit OSD nodes, one has bigger problems than just RAM. Eg. maybe one filled all DIMM slots with small-capacity modules and retrofitting would mean throwing a bunch of them away. Anyone remember how the Sun 4/110 was shipped back in the day if ordered with minimum RAM? Or the similar crap that NCD pulled? So basically I agree that there’s little or no benefit to it. Especially if only 5% of physmem as suggested below — a tiny amount of swap has a tiny benefit at best. In other words, if you really do need swap, arguably what you REALLY need is more RAM. I suggest that the OP has swap configured because NVMe is mentioned, perhaps there’s the idea that swap on NVMe is fast enough to be usable without horquing user experience. But that was only slightly implied, in the OP’s deployment it’s still possible that the swap is on a SATA/SAS/etc. boot drive, not NVMe. Swap on any kind of SSD is going to add unnecessary wear, esp. if you provision low-durability drives.