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Stop making swap partitions—use swap files instead

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Re: Stop making swap partitions—use swap files instead

#31

Post by pndc »

ducktective wrote: post #14

Tangential, but does anyone know why in 2026 and on Debian 13, my machine still hangs when some process exhausts RAM? Is there really no higher-priority kernel process to prevent total freeze of the system and send a SIGKILL to the culprit process when such a scenario happens?

I had a 1GB Debian VM which started freezing (requiring a hard reboot) after a routine aptitude upgrade to apply security patches. It was indeed caused by low memory, but not out of memory as there was still enough swap space remaining.

The culprit turned out to be the kernel itself, and rolling back to a 6.1 series kernel made the problem go away. I see that Linus's love for vibe-coding is already paying dividends.

Re: Stop making swap partitions—use swap files instead

#34

Post by cedilla »

killerstorm wrote: post #19
pasc1878 wrote: post #12

Earlier quoted context omitted.

MacOS seems to have no problem with hibernating and it and its predecessor NeXT have been using swap files for over 30 years.

MacOS has no problem with hibernation because hardware and software are designed together: it uses TPM to manage swap encryption. I assume "BIOS" is also optimized to enable fast boot on sleep. Linux can work with TPM but it's never as smooth. (Unless I guess you make it custom for your specific setup.)

I have FDE with keys in the TPM. It's pretty smooth bit required a one time additional step in Fedora. It's also probably not very secure, but my threat model is simple theft.

Re: Stop making swap partitions—use swap files instead

#35

Post by BoredomIsFun »

ducktective wrote: post #14

Tangential, but does anyone know why in 2026 and on Debian 13, my machine still hangs when some process exhausts RAM? Is there really no higher-priority kernel process to prevent total freeze of the system and send a SIGKILL to the culprit process when such a scenario happens?

It does not if you switch swapp off and use zram instead. I am typing right now on such a setup wityh 16 GiB ram and it occasionally, once a week or so, kills my firefox due to oom.

If you are you using disk swap - not sure why would if you have a SSD, but I once heard some justification for doing that - then install early OOM.

Re: Stop making swap partitions—use swap files instead

#36

Post by jenders »

Kim_Bruning wrote: post #11

Every rule has an exception. Beware of this advice on zfs, for instance. Meanwhile zswap (of no relation with zfs) is free performance. Is it a rule that everything starting with a 'z' must be cool?

That’s a good call out. I’ve never used ZFS on root. Been a ZFS user on Linux since the FUSE days but it has never seemed particular well suited (O_DIRECT support came late, ARC/page cache redundancy, etc). I can’t guarantee a consistent enough workload to optimize ZFS for and I don’t feel like it’s general purpose enough. Large object storage though? I’m sitting on a PB of ZFS.

Re: Stop making swap partitions—use swap files instead

#37

Post by holowoodman »

jenders wrote: post #32
holowoodman wrote: post #9

Stop using partitions. Use LVM!

How often are you needing to change partition geometry after install, on a server?

Depends. Some customers do run a lot of "pets, not cattle" servers, and those can get a few extra hard disks if space runs out. Some security guidelines prescribe separate volumes/filesystems for e.g. /home or /var/log, so log spam doesn't kill the whole system as easily. But of course, this means that sometimes the initial sizes aren't right and you need to extend something. In those cases, which happen a few times per year, not using LVM would be a huge problem.

But even for the "frequently reinstalled cattle"-usecase, LVM has benefits, e.g. snapshots for backups, debugging and forensics.

Re: Stop making swap partitions—use swap files instead

#38

Post by crabbone »

Oh, the irony of:

    echo "/swapfile none swap defaults 0 0" >> /etc/fstab
If we are going full modern, why not create a Systemd unit? ( https://www.freedesktop.org/software/systemd/man/latest/syst... ) if you need more info. If you didn't know this: /etc/fstab is not used directly after the pivot. Systemd parses it, creates units for every record in it, and that's what gets executed in reality. I can't imagine why would you want a swap file before pivot.

Re: Stop making swap partitions—use swap files instead

#39

Post by fc417fc802 »

optionalsquid wrote: post #27
Kim_Bruning wrote: post #11

Every rule has an exception. Beware of this advice on zfs, for instance. Meanwhile zswap (of no relation with zfs) is free performance. Is it a rule that everything starting with a 'z' must be cool?

It also doesn't sound like a particularly good idea on BTRFS, judging by the linked documentation: https://btrfs.readthedocs.io/en/latest/Swapfile.html

And since you should probably be running a modern CoW filesystem then you probably shouldn't be using swapfiles ... is the conclusion I arrived at anyway. Either install multiple times more RAM than you need and enable zswap or else set aside a swap partition as has always been done.

Re: Stop making swap partitions—use swap files instead

#40

Post by wongarsu »

fc417fc802 wrote: post #29
ducktective wrote: post #14

Tangential, but does anyone know why in 2026 and on Debian 13, my machine still hangs when some process exhausts RAM? Is there really no higher-priority kernel process to prevent total freeze of the system and send a SIGKILL to the culprit process when such a scenario happens?

> does anyone know why In a nutshell, overcommit. It's more or less broken by design but it's also incredibly practical so pretty much everyone does it. Couple that with the fact that it's difficult bordering on impossible to correctly determine the culprit. If you've got 16 GB RAM and the user launches 3 processes each of which attempts to use 8 GB who should you kill?

Notably windows doesn't use overcommit, and degrades much more gracefully under memory pressure. The biggest tradeoff is the amount of disk space consumed by a page file that also has to reserve space for unused pages that have been allocated but never been swapped in. On linux you can turn overcommit off, but there's too much software written around the assumption that overcommit is on
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