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Comment by ghostly_s | Hacker News Reader

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Respectfully, what a stubborn position to take. You don't want to listen to anyone else, and you don't want to be taught any new information about it that might change your mind.

Debian supports swap files and has information about setting them up in the Debian wiki, so I don't know why you're implying they've taken a stand on the issue.

Also, this seems to be based on a email from 2005, about kernel version 2.4 and 2.6, and their differences. Things might have changed since then, and also depends on a lot of factors, not the least what filesystem you use. I'm not sure people should seriously follow advice that basically boils down to "do this always it's best".

Better instead to make yourself informed about the tradeoffs, then make your own choice, for your setup.

Just because there might exist tradeoffs doesn’t make them matter to someone. If you’re using a Linux distro then you’re already living off thousands of decisions made with tradeoffs and it’s hardly feasible to be informed or care about all of them.

This recommendation is based off the current implementation.

See:

https://github.com/torvalds/linux/blob/827751b699b79a6e56998...

The thread is quoted to show that they have been functionally equivalent for several decades and yet distros continue to push outdated recommendations.

> yet distros continue to push outdated recommendations

Is it possible perhaps that this advice doesn't apply equally to all situations? Is it the best for people on ZFS? Is it the best for distributions that have their own kernels builds?

I'm not saying it's a bad default, or that people should avoid it, just that it's likely not "the absolute best no questions asked" regardless of the situation, that was what I was trying to point out with my previous comment.

This is one of the most anti-intellectual and unsuitable for HN comments I've ever seen.

You're proudly proclaiming your lack of desire to learn or discuss on a forum meant for those things.

Go to Reddit. That's the right place for you.

It's actually incredibly sensible not to just make changes to core OS settings unless you know what you're doing. There are good reasons not to use swap files, which become evident in OOM situations.

How does a swap file vs swap partition change things in OOM situations?

One traditional reason to prefer a swap partition was that the filesystem driver might have to allocate memory. I think swap files bypass the filesystem driver, though - getting the block extents and then accessing the block device at those locations, instead of accessing the file.

As @mitxela says, if you need to fault in a page which is needed for some critical OS function, which requires going through the VFS layer, and that requires paging in another page, which has been swapped out due to memory pressure ... There are many edge cases.

Swap on primary partitions also complicates dump and restore, although hardly anyone seems to know what backups are now.

See, the thing is that swapping or paging to a file does not use the VFS layer, except when activating or deactivating it. So swapfiles may not be materially different from swap partitions during operations.

https://utcc.utoronto.ca/~cks/space/blog/linux/HowSwapFindsB...

And there are many things that complicate dump and restore. Dump and restore often need to account for what partitions were created, anyway, so don't swap partitions also complicate it?

https://utcc.utoronto.ca/~cks/space/blog/sysadmin/SwapfileAn...

The swap files do use a non+VFS path after setup in 2.6+ kernels, but it is complex and has had bugs:

https://lkml.iu.edu/hypermail/linux/kernel/2103.0/06524.html

The bug is in here: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...

This was 2021, and while this bug is fixed, maybe take Linus's advice. Rely on a partition for primary swap, and only add files if you need to. Don't put them on the root partition, preferably a second disk.

I can't resolve your links but this is a good reference: https://kernel-internals.org/mm/swapping/

Normally dump skips swap partitions entirely, and doesn't know anything about partitioning. Swap will refuse to activate on a non-mkswap partition so there is reasonable protection when you're migrating.

BTW you can swap over NFS and iSCSI with swap files, with NFSoIB, or use the Infiniswap modules:

https://github.com/SymbioticLab/Infiniswap

Great hack for when you have a massive working set but don't want to rewrite the code to be distributed/parallel.

Ah the old HN hug. I’ll fix it

What bug?

"Hug", not bug. Referring to a site (presumably under OP's control) crashing due to increased traffic from HN.

But how are they going to fix the hug?

Buying more instances to serve it, I presume.

The hug of death.

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