I'd like to use another machine's unused RAM as swapspace for my primary Linux installation. I was just curious about performance of network ramdisks compared to local (slow) mechanical hard disks.

The swapfile is on a tmpfs mountpoint and is shared through samba. However, every time I try to issue:

swapon /mnt/ramswap/swapfile

I get:

swapon: /mnt/ramswap/swapfile: swapon failed: Invalid argument

and in dmesg I read:

[ 9569.806483] swapon: swapfile has holes

I've tried to allocate the swapfile with dd if=/dev/zero of=swapfile bs=1024 (but also =4096 and =1048576) and with truncate -s 2G (both followed by mkswap swapfile) but the result is always the same.

In this post (dated back to 2002) someone says that using a swapfile over NFS/SMB is not possible in Linux. Is this statement still valid? And if yes, what is the reason of this choice and is there any workaround to have this working?