https://wiki.archlinux.org/index.php/Uswsusp

Step A:

install https://aur.archlinux.org/packages/us/uswsusp-git/uswsusp-git.tar.gz

tar zxf uswsusp-git.tar.gz

makepkg

pacman -U uswsusp-git-xxxx-1-x86_64.pkg.tar.xz

em /etc/suspend.conf

like this:

snapshot device = /dev/snapshot
resume device = /dev/sda5
resume offset = 123456                                          <----# swap-offset <swap_file_path>
shutdown method = platform
compress = y

Step B:

1) Create the swap file and make it active, eg.

# dd if=/dev/zero of=<swap_file_path> bs=1024 count=<swap_file_size_in_k>

# mkswap <swap_file_path>

# swapon <swap_file_path>

 2) Use an application that will bmap the swap file with the help of the

 FIBMAP ioctl and determine the location of the file's swap header, as the

 offset, in <PAGE_SIZE> units, from the beginning of the partition which

 holds the swap file.

# swap-offset <swap_file_path>

next line maybe useless

 3) Add the following parameters to the kernel command line:

 resume=<swap_file_partition> resume_offset=<swap_file_offset>

Step C:

s2disk