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I have configured hibernate, its working, just to make sure it will not fail sometime - this question.

I have two swap files on different devices, first is small swap on SSD, second as big as ram on HDD. Hibernate configured to small one. It works fine for now, as hibernate not always requires too much(not everything written or compressed, I don't known).

How to configure hibernate to use both swaps? Or it process them automatically and nothing need to do? At kernel options I have setup for first small swap, and its good if it will use it first(as fastest) and then second.

I don't want to make SSD swap larger as SSD is small.

leonid@DevSSD:~$ grep resume < /etc/default/grub

GRUB_CMDLINE_LINUX_DEFAULT="no_console_suspend initcall_debug resume=UUID=050f8852-d8f6-4979-a4e4-c3d9b981bee9 resume_offset=34816"

/etc/fstab

UUID=050f8852-d8f6-4979-a4e4-c3d9b981bee9   /   ext4    relatime,grpquota,data=ordered,usrquota,rw,errors=remount-ro,quota  0   1

UUID=3bcf1591-7033-416a-addf-9cf8e2e10c93   /home/leonid/hdd    ext4    defaults,rw,errors=remount-ro   0   1

/swapfile                   none    swap    sw  0   0

/home/leonid/hdd/swapfile   none    swap    sw  0   0

UUID=26DA-1C76  /boot/efi   vfat    defaults    0   1

Update:
I have make even smaller swap for testing and setup priority. Hibernating not goes to swap with higher priority:

leonid@DevSSD:~$ swapon

NAME                      TYPE SIZE USED PRIO

/swap64k                  file  60K   0B    1

/home/leonid/hdd/swapfile file   8G   0B  100

leonid@DevSSD:~$ systemctl hibernate

Failed to hibernate system via logind: Sleep verb not supported

In short, no you have to use a single file or partition for hibernation.

TL;DR

There is nothing in the basic kernel documentation for Sleep States or Power Interface which says that the swap has to be in a single file. Indeed, there is some indication that the hibernation data is written to available swap space on the computer:

However, further exploration leads us to the documents for swsusp which has a short FAQ section, and the quote

Q: Does swsusp (to disk) use only one swap partition or can it use
multiple swap partitions (aggregate them into one logical space)?

A: Only one swap partition, sorry.

Although this only speaks directly to partitions I would certainly interpret this as applying to swap spaces on your machine.

Your potential problem of "What if there is not enough space on my swap file". Here we run into some vagueness. The documentation assures us that the system will attempt by default to create an image about 2/5th the size of memory:

/sys/power/image_size controls the size of hibernation images.

It can be written a string representing a non-negative integer that
will be used as a best-effort upper limit of the image size, in bytes.
The hibernation core will do its best to ensure that the image size
will not exceed that number. However, if that turns out to be
impossible to achieve, a hibernation image will still be created and
its size will be as small as possible. In particular, writing '0' to
this file will enforce hibernation images to be as small as possible.

However the documents to not indicate what might happen if the image exceeds swap size. My own experience when I have accidenatly had swap turned off and tried to hibernate, is that nothing happens.

LATER EDIT

Does this say something about me, Ubuntu users or Linux users?

I was curious about what happens if the swapfile is too small, so I created a 44KB swapfile (that worked!) and tried to hibernate:

chick@dad:~$ swapon

NAME   TYPE SIZE USED PRIO

/swap2 file  44K   0B   -2

chick@dad:~$ sudo systemctl hibernate

Failed to hibernate system via logind: Not enough swap space for hibernation

I further tested by using two swapfiles, the smaller one being higher priority:

chick@dad:~$ sudo swapon /swap2 -p 1

chick@dad:~$ sudo swapon /swapfile -p 2

chick@dad:~$ swapon

NAME      TYPE SIZE USED PRIO

/swap2    file  44K   0B    1

/swapfile file  16G   0B    2

chick@dad:~$ sudo systemctl hibernate

Failed to hibernate system via logind: Not enough swap space for hibernation