1. System suspend
(short version)
Pavel Machek,
SUSE Labs
7/4/2018

2. Suspend to RAM
a.k.a. S3
we have enough kernel support that it works on most machines, with exception of video
ugly hacks were developed to fix video
better keep them in userland
suspend.sf.net tries to integrate them in easy-to-use package
being easy-to-use introduced problems on lots of strange machines, Stefan Seyfried is working with users on expanding whitelist.
contains DMI-based whitelist of notebooks

3. Using suspend to RAM ./s2ram
If it does not work, see opensuse website for nice troubleshooting guide.
what to do with desktops? Match both DMI and PCI ID of the video card? What about multihead setups?
fortunately (?) it seems that noone cares
HAL integration?

4. Brief history
'Software suspend' or 'Swap suspend'
Swsusp
* suspend-to-disk done by linux kernel, does not need BIOS support
* originally for 2.4.X by Gabor Kuti
* Nigel forked suspend2
* I created proof-of-concept uswsusp-like patches in late 2006
* Rafael added uswsusp in rc1

5. Swsusp Very simple, in-kernel implementation
Can use swap partition (no need for dedicated partition)
Faster than BIOS suspend-to-disk (but slower than suspend2/uswsusp)
Supports SMP, HIGHMEM, etc
i386, x86-64, frv, ppc32
optionaly saves up to 50% of memory (including caches)
stable: SUSE ships/supports it (in openSUSE <= 10.1)
Fedora ships it
still possible to shoot yourself into the foot, fortunately distros make it hard

6. Nigel's suspend2 All the features possible, and then some more
Up to 100% of memory saved
Encryption, compression support
Can suspend to regular file and swapfile
Bootsplash integration, esc aborts suspend
Complex
14K LoC of kernel code
Homebrew plugins support
UI in kernel
Fortunately (?) I scared Nigel away by now?

7. uSwsusp Allows userland to do all the hard work
Kernel only exports low-level functions
This allows to keep kernel complexity low (~1K LoC) while retaining flexibility
Userland code available at suspend.sf.net
Supports compression, encryption (password only asked during resume), suspend to file (slightly hacky, -mm?)
Abort by key, bootsplash support
Suspending over network should be doable without kernel patches

8. Suspend to both
uSwsusp enables us to support „store image on disk, then suspend to RAM“
gets you fast resume, without risk of loosing data when battery runs flat
Experimental, but quite simple
Relies on s2ram being single binary