Hi,

After a boot this evening when back home:

$ cat /proc/swaps 
Filename				Type		Size	Used	Priority
/dev/zram0                              partition	947216	0	100
/dev/sda6                               partition	4607996	0	-1
$

**Only one device is created, and it has a 100 priority! (zram-config usually creates it with priority 5).


$ systemctl list-units | grep zram
  sys-devices-virtual-block-zram0.device                                                                loaded active plugged   /sys/devices/virtual/block/zram0
● zram-config.service                                                                                   loaded failed failed    Initializes zram swaping
  dev-zram0.swap                                                                                        loaded active active    /dev/zram0
$ apt-cache policy zram-config
zram-config:
  Installé : 0.3.1
  Candidat : 0.3.1
 Table de version :
 *** 0.3.1 0
        500 http://archive.ubuntu.com/ubuntu/ vivid-proposed/universe amd64 Packages
        100 /var/lib/dpkg/status
     0.3 0
        500 http://archive.ubuntu.com/ubuntu/ vivid/universe amd64 Packages
[melodie@bento64:~]$ 

=-=-=-=-=

then:

$ LANG=C systemctl status zram-config.service -l
* zram-config.service - Initializes zram swaping
   Loaded: loaded (/lib/systemd/system/zram-config.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Tue 2015-06-16 20:50:26 CEST; 1h 59min ago
  Process: 701 ExecStart=/usr/bin/init-zram-swapping (code=exited, status=255)
 Main PID: 701 (code=exited, status=255)

Jun 16 20:50:22 bento64 init-zram-swapping[701]: sh: echo: I/O error
Jun 16 20:50:22 bento64 init-zram-swapping[701]: mkswap: error: /dev/zram0 is mounted; will not make swapspace
Jun 16 20:50:22 bento64 init-zram-swapping[701]: swapon: /dev/zram0 : échec de swapon: Périphérique ou ressource occupé
Jun 16 20:50:22 bento64 init-zram-swapping[701]: /usr/bin/init-zram-swapping: 21: /usr/bin/init-zram-swapping: cannot create /sys/block/zram1/disksize: Directory nonexistent
Jun 16 20:50:22 bento64 init-zram-swapping[701]: /dev/zram1: Aucun fichier ou dossier de ce type
Jun 16 20:50:22 bento64 init-zram-swapping[701]: swapon: stat failed /dev/zram1: Aucun fichier ou dossier de ce type
Jun 16 20:50:26 bento64 systemd[1]: zram-config.service: main process exited, code=exited, status=255/n/a
Jun 16 20:50:26 bento64 systemd[1]: Failed to start Initializes zram swaping.
Jun 16 20:50:26 bento64 systemd[1]: Unit zram-config.service entered failed state.
Jun 16 20:50:26 bento64 systemd[1]: zram-config.service failed.
$ 


What else? Yes more information here:

$ uname -a
Linux bento64 3.19.0-21-generic #21-Ubuntu SMP Sun Jun 14 18:31:11 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
$

and also here about zram module:
$ cd /lib/modules
$ find . -name "zram*"
./3.19.0-18-generic/kernel/drivers/block/zram
./3.19.0-18-generic/kernel/drivers/block/zram/zram.ko
./3.19.0-20-generic/kernel/drivers/block/zram
./3.19.0-20-generic/kernel/drivers/block/zram/zram.ko
./3.19.0-21-generic/kernel/drivers/block/zram
./3.19.0-21-generic/kernel/drivers/block/zram/zram.ko
$ 

I wasn't aware it wasn't in the staging directory anymore. And about "is it loaded and how?":

$ grep ZRAM /boot/config-3.19.0-21-generic 
CONFIG_ZRAM=m
CONFIG_ZRAM_LZ4_COMPRESS=y
# CONFIG_ZRAM_DEBUG is not set
$

What about lsmod? 
$ lsmod | grep zram
zram                   24576  1 
lz4_compress           16384  1 zram
$ 


What do you think? How is zram loaded?

Here is a scheme brought by "systemd-analyze plot" (can that help?)
http://citrotux.org/Downloads/plot.svg