After linux 5.0, swapfile is supported on BTRFS. However I found the hibernation does not work correctly on 5.0 kernel.
Distro: Arch Linux
$ truncate -s 0 /swapfile
$ chattr +C /swapfile
$ fallocate -l 32G /swapfile
$ chmod 0600 /swapfile
$ mkswap /swapfile
# Add /swapfile to /etc/fstab
swapfile works correctly as swap memory
$ filefrag -v /swapfile
Get the physical offset of first extent as 57869156
Added kernel parameter
After rebooting try hibernate with systemctl hibernate
The hibernation failed after blanking the screen and dmesg shows:
PM: Cannot find swap device, try swapon -a
BTW, the similar setup swapfile works correctly to hibernate with ext4 file system or swap partition.
BTW after hibernation failure and dmesg showing Cannot find swap device, try swapon -a. swapon shows the swapfile is functioning correctly. Running swapon -a does not help the issue.
Adding Omar to CC.
This is because on Btrfs, the "physical" offset you get from filefrag isn't the real physical offset on disk; we have a virtual disk address space in order to support multiple devices. I'll hack up a tool you can use to get the actual physical offset on Btrfs.
Thanks Omar for the explanation. Let me know when you have the tool to get the actual physical offset on Btrfs.
Later, do we need to implement the functionality in e2fsprogs we can have the tool to get actual physical address?
Also we may need to update the man 5 btrfs.
Please try out https://github.com/osandov/osandov-linux/blob/master/scripts/btrfs_map_physical.c
It should compile with `gcc -O2 -o btrfs_map_physical btrfs_map_physical.c`. Run it with `./btrfs_map_physical /swapfile | column -ts $'\t'`. resume_offset should be the first physical offset.
Thanks Omar for the tool
I tried to run:
$ sudo ./btrfs_map_physical /swapfile | column -ts $'\t'
'FILE OFFSET EXTENT TYPE LOGICAL SIZE LOGICAL OFFSET PHYSICAL SIZE DEVID PHYSICAL OFFSET
0 regular 4096 248324816896 268435456 1 216112562176
4096 prealloc 268431360 248324820992 268431360 1 216112566272
268435456 prealloc 268435456 248593252352 268435456 1 216380997632
536870912 prealloc 268435456 248861687808 268435456 1 216649433088
805306368 prealloc 268435456 249130123264 268435456 1 241613930496
1073741824 prealloc 268435456 249398558720 268435456 1 241882365952
1342177280 prealloc 268435456 249666994176 268435456 1 242150801408
1610612736 prealloc 268435456 249935429632 268435456 1 242419236864
1879048192 prealloc 268435456 250203865088 268435456 1 242687672320
2147483648 prealloc 268435456 250472300544 268435456 1 242956107776
2415919104 prealloc 268435456 250740736000 268435456 1 243224543232
I used offset 216112562176 in kernel parameter:
NAME TYPE SIZE USED PRIO
/swapfile file 16G 0B -2
Run hibernate, I still got error:
[ 26.828436] PM: Cannot find swap device, try swapon -a
[ 26.828441] PM: Cannot get swap writer
Ah, apparently the unit is pages, so if this is x86, it should be 216112562176 / 4096 = 52761856. Also, `systemctl hibernate` seems to override those settings incorrectly. Can you try `echo disk > /sys/power/state` instead?
Yup, systemd overrides what you configure on the command line with the result of fiemap and stat, neither of which correspond to the physical device on Btrfs.
Thanks for the tool. Works for me with `echo disk > /sys/power/state` and
$ sudo ./btrfs_map_physical /.swap/swapfile | column -ts $'\t' | head -n2
FILE OFFSET EXTENT TYPE LOGICAL SIZE LOGICAL OFFSET PHYSICAL SIZE DEVID PHYSICAL OFFSET
0 regular 4096 2407055360 268435456 1 2407055360
GRUB_CMDLINE_LINUX="cryptdevice=PARTLABEL=cryptsystem:cryptroot resume=/dev/mapper/cryptroot resume_offset=587660"
Ah, I see. `echo disk > /sys/power/state` works with offset pages.
I filed a bug in systemd tracker also:
(In reply to Liberty from comment #10)
> Ah, I see. `echo disk > /sys/power/state` works with offset pages.
> I filed a bug in systemd tracker also:
I've pushed a proposed fix for the systemd bug which checks for and honours previously set resume_offset values before attempting to calculate it. If anybody wants to give it a try to confirm it works (or not) with their setup, that would be helpful. https://github.com/systemd/systemd/pull/12760
(In reply to Zach Smith from comment #11)
> (In reply to Liberty from comment #10)
> > Ah, I see. `echo disk > /sys/power/state` works with offset pages.
> > I filed a bug in systemd tracker also:
> > https://github.com/systemd/systemd/issues/11939
> I've pushed a proposed fix for the systemd bug which checks for and honours
> previously set resume_offset values before attempting to calculate it. If
> anybody wants to give it a try to confirm it works (or not) with their
> setup, that would be helpful. https://github.com/systemd/systemd/pull/12760
This issue should be resolved with the merge of PR https://github.com/systemd/systemd/pull/12760 and issue https://github.com/systemd/systemd/issues/11939 has been closed.
Yes, I have verified that systemd and btrfs swapfile working. The only pending issue is that we need to use Omar's script to calculate the physical offset of btrfs swapfile.