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Paging out to disk is not going to go away until memory gets as cheap as disk or until we get much better at eliminating loading to memory stuff that is not use

Paging out to disk is not going to go away until memory gets as cheap as disk or until we get much better at eliminating loading to memory stuff that is not useful. When you have a server with virtual machines, you have a bunch of stuff in memory that just isn't all that useful. This might be libraries and functionalities nobody uses, parts of memory of processes that is used only at startup, etc. It is always better to page that memory to the disk so that the memory can be actively used to serve demand. While it is nice to have application fail in controlled manner when it allocates memory, the reality datacenter life is that once a process hits memory limit it can no longer be trusted to behave correctly and should be restarted, ideally along with entire instance. It is far better to have something kill the process than have the process try to continue after failed allocation request as most processes are not very well tested with regards to failing at random allocation and continue with no possibility to allocate more memory.

eru 6y ago
> When you have a server with virtual machines, you have a bunch of stuff in memory that just isn't all that useful. This might be libraries and functionalities nobody uses, parts of memory of processes that is used only at startup, etc. > It is always better to page that memory to the disk so that the memory can be actively used to serve demand. That's a good point. But interestingly, not a strong enough one to make eg Google turn on paging out to disk nor ssd. (At least not a few years ago. No clue if they do that these days.) Perhaps what you would want is a hybrid: let the OS page stuff out by default so you can free up the libraries and startup code and data structures etc. But if your disk hits some thrashing threshold because the working sets get larger than memory, let some variant of OOM killer loose?
- offlinemark 6y ago
  > Perhaps what you would want is a hybrid: let the OS page stuff out by default so you can free up the libraries and startup code and data structures etc. But if your disk hits some thrashing threshold because the working sets get larger than memory, let some variant of OOM killer loose? Linux does a form of this. File mappings are paged out to disk (reclaimed) by default, and the OOM killer is only triggered if this is not enough. This gets you pretty far, as it includes all binaries and libraries.
  - eru 6y ago
    Oh, true. My suggestion would mostly only add paging out of seldom used data structures.

eru 6y ago

> When you have a server with virtual machines, you have a bunch of stuff in memory that just isn't all that useful. This might be libraries and functionalities nobody uses, parts of memory of processes that is used only at startup, etc. > It is always better to page that memory to the disk so that the memory can be actively used to serve demand. That's a good point. But interestingly, not a strong enough one to make eg Google turn on paging out to disk nor ssd. (At least not a few years ago. No clue if they do that these days.) Perhaps what you would want is a hybrid: let the OS page stuff out by default so you can free up the libraries and startup code and data structures etc. But if your disk hits some thrashing threshold because the working sets get larger than memory, let some variant of OOM killer loose?

offlinemark 6y ago
> Perhaps what you would want is a hybrid: let the OS page stuff out by default so you can free up the libraries and startup code and data structures etc. But if your disk hits some thrashing threshold because the working sets get larger than memory, let some variant of OOM killer loose? Linux does a form of this. File mappings are paged out to disk (reclaimed) by default, and the OOM killer is only triggered if this is not enough. This gets you pretty far, as it includes all binaries and libraries.
- eru 6y ago
  Oh, true. My suggestion would mostly only add paging out of seldom used data structures.