Bug 987136

Summary:	RFE: add 'discard' swap option support for /etc/fstab
Product:	[Fedora] Fedora	Reporter:	Carl Roth <roth>
Component:	systemd	Assignee:	Jan Synacek <jsynacek>
Status:	CLOSED RAWHIDE	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	medium	Docs Contact:
Priority:	unspecified
Version:	rawhide	CC:	johannbg, jsynacek, lnykryn, msekleta, plautrba, roth, rvokal, systemd-maint, vpavlin, zbyszek
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Hardware:	Unspecified
OS:	Unspecified
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Fixed In Version:	systemd-216-4.fc21	Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2014-10-17 17:10:58 UTC	Type:	Bug
Regression:	---	Mount Type:	---
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Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
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Embargoed:

Description Carl Roth 2013-07-22 19:11:00 UTC

Description of problem:

systemd-fstab-generator ignores the 'discard' mount option in /etc/fstab for swap partitions.  Additionally, there is no syntax in the systemd.swap unit files to specify this feature.

Version-Release number of selected component (if applicable):

systemd-201-2.fc18.7.x86_64

How reproducible:

always

Steps to Reproduce:
1. 
2. 
3.

Actual results:


Expected results:


Additional info:

It's an open question how to actually tell if a swap partition is using 'discard' (not systemd-specific).  It's definitely the case that the option is not reflected in the unit file.

Comment 1 Carl Roth 2013-07-22 20:37:22 UTC

If the dmesg results are to be believed, I think this is the difference between 'discard' and 'no discard' (see the 'D' flag):

# swapon /dev/disk/by-uuid/d8e4b4bf-9f1e-446a-a5b0-0325c4ef7d73
# dmesg | grep swap | tail -1
[773331.002898] Adding 8388604k swap on /dev/mapper/M4_CT256_AF15-scruffy_f18_swap.  Priority:-1 extents:1 across:8388604k SS

# swapon --discard /dev/disk/by-uuid/d8e4b4bf-9f1e-446a-a5b0-0325c4ef7d73
# dmesg | grep swap | tail -1
[773346.691092] Adding 8388604k swap on /dev/mapper/M4_CT256_AF15-scruffy_f18_swap.  Priority:-1 extents:1 across:8388604k SSD

More importantly, my /etc/fstab lists that partition with the 'discard' option, and at boot time the option is ignored (presumably because of systemd):
# dmesg | grep swap | head -1
[    2.527089] Adding 8388604k swap on /dev/mapper/M4_CT256_AF15-scruffy_f18_swap.  Priority:-1 extents:1 across:8388604k SS

So this is more of a general systemd/bootup problem.

Comment 2 Carl Roth 2013-07-22 20:39:04 UTC

As per

http://cgit.freedesktop.org/systemd/systemd/tree/src/core/swap.c

this is not currently a supported feature in systemd.

Comment 3 Carl Roth 2013-07-22 20:46:47 UTC

(In reply to Carl Roth from comment #1)
> If the dmesg results are to be believed, I think this is the difference
> between 'discard' and 'no discard' (see the 'D' flag):

Found it at

http://lxr.free-electrons.com/source/mm/swapfile.c?v=3.9#L2136

Comment 4 Lennart Poettering 2014-06-19 18:56:08 UTC

Does "swapon -a" read this from fstab? We should probably support the same syntax.

Comment 5 Carl Roth 2014-06-19 19:43:46 UTC

(In reply to Lennart Poettering from comment #4)
> Does "swapon -a" read this from fstab? We should probably support the same
> syntax.

Yes, see

https://git.kernel.org/cgit/utils/util-linux/util-linux.git/tree/sys-utils/swapon.c#n640

Comment 6 Jan Synacek 2014-09-30 05:52:50 UTC

http://cgit.freedesktop.org/systemd/systemd/commit/?id=86b23b07c96b185126bfbf217227dad362a20c25
http://cgit.freedesktop.org/systemd/systemd/commit/?id=4f52d3fe2da7c3449b7fbfaa7c64a83354d3b56c
http://cgit.freedesktop.org/systemd/systemd/commit/?id=cdc8982030271785d650af410230397bbb5a4be9
http://cgit.freedesktop.org/systemd/systemd/commit/?id=4afbccded23f5144e39a7f7b243393799186ba39