alt Hacker NewsWhich is a major way turning off overcommit can cause problems. The expectation for disabling it is that if you request memory you're going to use it, which is frequently not true. So if you turn it off, your memory requirements go from, say, 64GB to 512GB.
Obviously you don't want to have to octuple your physical memory for pages that will never be used, especially these days, so the typical way around that is to allocate a lot of swap. Then the allocations that aren't actually used can be backed by swap instead of RAM.
Except then you've essentially reimplemented overcommit. Allocations report success because you have plenty of swap but if you try to really use that much the system grinds to a halt.
> your memory requirements go from, say, 64GB to 512GB.
Then your memory requirements always were potentially 512GB. It may just happen to be even with that amount of allocation you may only need 64GB of actual physical storage; however, there is clearly a path for your application to suddenly require 512GB of storage. Perhaps when it's under an attack or facing misconfigured clients.
If your failure strategy is "just let the server fall over under pressure" then this might be fine for you.