Bug 181565

Summary:	[swap] Problem with vnode-backed swap space.
Product:	Base System	Reporter:	Eddy Beaupré <eddy>
Component:	kern	Assignee:	freebsd-fs (Nobody) <fs>
Status:	In Progress ---
Severity:	Affects Only Me	CC:	elij+freebsd, marklmi26-fbsd, rs, zsolt.ero
Priority:	Normal
Version:	10.0-CURRENT
Hardware:	Any
OS:	Any

Description Eddy Beaupré 2013-08-26 16:00:00 UTC

Vnode-backed swap space doesn't seem to work at boot. md0 is created but the swap memory is not added to the system and swapon complain that it is already in use.

Manually releasing md0 (mdconfig -d -u0) and running swapon -a fix the problem but must be done at every boot.

My fstab entry for the swapfile is the following:

md   none   swap   sw,file=/var/spool/swap/swapfile   0   0

Fix: 

More a workaround, once boot do the following as root:

# mdconfig -d -u0
# swapon -a
How-To-Repeat: 1) Add a swafile via /etc/fstab:
md   none   swap   sw,file=/var/spool/swap/swapfile   0   0

2) reboot the system and check if the swapfile is avalable.

Comment 1 Mark Linimon freebsd_committer

2013-08-27 02:49:31 UTC

Responsible Changed
From-To: freebsd-bugs->freebsd-fs

Make a random assignment.

Comment 2 elij 2014-11-15 23:10:49 UTC

Having the same problem.

This worked on 10.0-RELEASE. After upgrading to 10.1-RELEASE, it no longer works.

/etc/fstab:
md99		none		swap	sw,file=/swap0  0	0

After boot:
# mdconfig -lv
md99	vnode	  256M	/swap0

# swapinfo 
Device          1K-blocks     Used    Avail Capacity
# 


Deleting the md and calling swapon by hand works.

# mdconfig -d -u 99; swapon -a; swapinfo -h
swapon: adding /dev/md99 as swap device
Device          1K-blocks     Used    Avail Capacity
/dev/md99          262144       0B     256M     0%

Comment 3 Robert Schulze 2016-01-22 15:43:09 UTC

If you add "late" to the mount options, it will work. This is not properly documented.

With kind regards,
Robert Schulze

Comment 4 Mark Millard 2016-01-22 22:35:27 UTC

FYI: See

Bug 206048 - 11.0-CURRENT -r293227 (and others) arm (rpi2/BeagleBone Black) amd64 etc: swapfile usage hangs; swap partition works

for a problem that may apply to 10.x as well when using things like:

file=/var/spool/swap/swapfile
file=/swap0

--unless those files are on their own file systems/partitions not used for other (used) files. (A swap file by itself on its own partition/file system has not shown the problem. Mixing with other IO from the same file system/partition does. But only so much information can be put in a subject line.)

It may be worth testing if the involved 10.x context(s) hang before settling on this sort of placement of the file. One of the comments suggested a command like:

stress -d 2 -m 3 --vm-keep

was sufficient to show the problem on at least 11.0-CURRENT amd64 contexts. I guess that command is from the port sysutils/stress .

It would actually be good to have 10.x comments in Bug 206048 reporting how such testing went if someone tries it.

Comment 5 Eitan Adler freebsd_committer

2018-05-28 12:32:36 UTC

*** Bug 204485 has been marked as a duplicate of this bug. ***