Ubuntu – Does Ubuntu support dynamic swap file sizing

17.04swap

I can't imagine why a swap file needs to be fixed size. Why not let it resize dynamically, like the hard drive image file for a virtual box?

Best Answer

It doesn't look like Linux supports dynamic swap file sizing (at any rate, I couldn't get it to detect that a swap file had changed size without a swapoff/swapon).

Presumably it is easier to assume that a swap file doesn't change file size dynamically when writing code for supporting it. I don't see any great use for it either. Since you can use multiple swap files, nothing's preventing you from creating more swap files as needed.

Also note this paragraph from the swapon manpage:

The  swap file implementation in the kernel expects to be able to write
to the file directly, without the assistance of the  filesystem.   This
is  a problem on preallocated files (e.g.  fallocate(1)) on filesystems
like XFS or ext4, and on copy-on-write filesystems like btrfs.

I'd think the same problem would apply to a dynamically-sized swap file.

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