Bug#911275: systemd: ignores swap options (discard) from /etc/fstab ?

[Bob Bib]

Package: systemd
Version: 232-25+deb9u4
Severity: normal

Dear Maintainer,

Apparently, systemd ignores swap options (namely, "discard") from 
"/etc/fstab";
i.e. my SSD swap partition gets activated, but with TRIM disabled.

For reference:
// 
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/swapfile.c?h=v4.9.133#n2567
pr_info("Adding %uk swap on %s.  Priority:%d extents:%d across:%lluk 
%s%s%s%s%s\n",
		p->pages<<(PAGE_SHIFT-10), name->name, p->prio,
		nr_extents, (unsigned long long)span<<(PAGE_SHIFT-10),
		(p->flags & SWP_SOLIDSTATE) ? "SS" : "",
		(p->flags & SWP_DISCARDABLE) ? "D" : "",
		(p->flags & SWP_AREA_DISCARD) ? "s" : "",
		(p->flags & SWP_PAGE_DISCARD) ? "c" : "",
		(frontswap_map) ? "FS" : "");

BTW, manually playing with discard options & swapoff/swapon has resulted
in the following (reasonable) changes
of the final word of the kernel message:
<no discard option> => SSFS
discard => SSDscFS
discard=pages => SSDcFS
discard=once => SSDsFS

P.S. I don't know whether the current issue is related to that old 
openSUSE bug,
but anyway I'm leaving these links here:
https://bugzilla.novell.com/show_bug.cgi?id=897422
https://github.com/systemd/systemd/commit/47cb901e38cd7092576fc8e76cc4a14f39bf719d

-- Package-specific info:

-- System Information:
Debian Release: 9.5
   APT prefers stable-updates
   APT policy: (500, 'stable-updates'), (500, 'stable')
Architecture: amd64 (x86_64)

Kernel: Linux 4.9.0-8-amd64 (SMP w/4 CPU cores)
Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 (charmap=UTF-8), 
LANGUAGE=en_US:en (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages systemd depends on:
ii  adduser         3.115
ii  libacl1         2.2.52-3+b1
ii  libapparmor1    2.11.0-3+deb9u2
ii  libaudit1       1:2.6.7-2
ii  libblkid1       2.29.2-1+deb9u1
ii  libc6           2.24-11+deb9u3
ii  libcap2         1:2.25-1
ii  libcryptsetup4  2:1.7.3-4
ii  libgcrypt20     1.7.6-2+deb9u3
ii  libgpg-error0   1.26-2
ii  libidn11        1.33-1
ii  libip4tc0       1.6.0+snapshot20161117-6
ii  libkmod2        23-2
ii  liblz4-1        0.0~r131-2+b1
ii  liblzma5        5.2.2-1.2+b1
ii  libmount1       2.29.2-1+deb9u1
ii  libpam0g        1.1.8-3.6
ii  libseccomp2     2.3.1-2.1
ii  libselinux1     2.6-3+b3
ii  libsystemd0     232-25+deb9u4
ii  mount           2.29.2-1+deb9u1
ii  procps          2:3.3.12-3+deb9u1
ii  util-linux      2.29.2-1+deb9u1

Versions of packages systemd recommends:
ii  dbus            1.10.26-0+deb9u1
ii  libpam-systemd  232-25+deb9u4

Versions of packages systemd suggests:
ii  policykit-1        0.105-18
pn  systemd-container  <none>
pn  systemd-ui         <none>

Versions of packages systemd is related to:
pn  dracut           <none>
ii  initramfs-tools  0.130
ii  udev             232-25+deb9u4

-- no debconf information

-- Some terminal output:
$ cat /etc/fstab
...
UUID=<UUID_4> none            swap    sw,discard=once              0       0
$ sudo swapoff -va
swapoff /dev/sda4
$ /sbin/swapon
$ sudo swapon -va
swapon: /dev/sda4: found signature [pagesize=4096, signature=swap]
swapon: /dev/sda4: pagesize=4096, swapsize=<size_0>, devsize=<size_0>
swapon /dev/sda4
$ sudo journalctl | grep -i swap
Oct 18 01:26:26 Computer1 kernel: zswap: loaded using pool lzo/zbud
Oct 18 01:26:26 Computer1 systemd[1]: Found device <SSD_model> Swap01.
Oct 18 01:26:26 Computer1 systemd[1]: Found device <SSD_model> Swap01.
Oct 18 01:26:26 Computer1 systemd[1]: Activating swap Swap Partition...
Oct 18 01:26:26 Computer1 kernel: Adding <size_1>k swap on /dev/sda4. 
Priority:-1 extents:1 across:<size>k SSFS
Oct 18 01:26:26 Computer1 systemd[1]: Activated swap Swap Partition.
Oct 18 01:26:26 Computer1 systemd[1]: Activated swap 
/dev/disk/by-uuid/<UUID_4>.
Oct 18 01:26:26 Computer1 systemd[1]: Reached target Swap.
Oct 18 01:27:14 Computer1 sudo[1049]:  user1 : TTY=tty1 ; 
PWD=/home/user1 ; USER=root ; COMMAND=/sbin/swapoff -va
Oct 18 01:27:27 Computer1 sudo[1057]:  user1 : TTY=tty1 ; 
PWD=/home/user1 ; USER=root ; COMMAND=/sbin/swapon -va
Oct 18 01:27:33 Computer1 kernel: Adding <size_1>k swap on /dev/sda4. 
Priority:-1 extents:1 across:<size>k SSDsFS

-- 
Best wishes,
Bob