Swapfile Swapon invalid argument

Question

I had swap from a swapfile working for quite some time, but for some reason it stopped working.
sudo fallocate -l 4G /home/.swap/swapfile
sudo chmod 600 /home/.swap/swapfile
sudo mkswap /home/.swap/swapfile

# /etc/fstab
/home/.swap/swapfile swap swap defaults 0 0

sudo swapon -a

swapon: /home/.swap/swapfile: swapon failed: Invalid argument
I'm running the newest version of Fedora, so is it maybe possible something has changed with an update or what could be the reason?

valecs · Answer

Building on the accepted answer with an explanation: 
Quoting from swapon(8):

Files with holes
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 files with holes or on copy-on-write files on filesystems like Btrfs.
Commands like cp(1) or truncate(1) create files with holes. 
These files will be rejected by swapon.
Preallocated files created by fallocate(1) may be interpreted as files with holes too depending of the filesystem. 
Preallocated swap  files are supported on XFS since Linux 4.18.
The most portable solution to create a swap file is to use dd(1) and /dev/zero.

The italicized note seems to explain everything. 
Unfortunately, even with verbose output,
swapon doesn't mention the cause (files with holes) of failure.

Artem S. Tashkinov · Answer

Please try replacing
fallocate -l 4G /home/.swap/swapfile
with
dd if=/dev/zero of=/home/.swap/swapfile bs=1M count=4096

Swapfile Swapon invalid argument

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