Software Suspend - Features

Software Suspend's features include:

Image compression (LZF - very fast and highly recommended).
Full asynchronous I/O and readahead for synchronous I/O for maximum throughput.
Multithreaded compression & I/O.
Support for any number of swap partitions and/or files.
The ability to cancel a suspend cycle (during suspending) by pressing escape.
The ability to specify a maximum image size.
Support for saving a full image of your memory, resulting in a fast, responsive system after resuming.
Support for plugins: data transformers (compression, encryption) and new storage backends (NFS support is planned).
Works out of the box for most configurations.
Nice user interface (GenSplash compatible).
Support for Highmem (up to 4GB), SMP and preemptive kernels.
Scripting support.
Speed and reliability - Software Suspend has been extensively tested in a variety of configurations over many months. It is not guaranteed to be perfect, but bugs found will be hunted and fixed quickly.
Can be configured to be a drop-in replacement for swsusp (for swap partitions - swap files are configured more simply with TuxOnIce).
Preliminary FUSE support.
(Work in progress:) Cluster support.

Suspend-to-disk implementations explained

Since the original Software Suspend code was written by Gabor Kuti and Pavel Machek back in 1998, four different implementations have been created for the 2.6 kernel, all forks of the same original codebase. Here is a quick comparison between the three that still exist. The first column refers to CONFIG_SOFTWARE_SUSPEND in the 2.6 kernel. pmdisk has been merged back into the original "swsusp" implementation in the kernel, and hence is no longer listed here. The second column refers to what is now commonly called "TuxOnIce" (previously Suspend2) and is what this site largely deals with. The third is userspace swsusp, developed by Rafael Wysocki.

Name	swsusp	TuxOnIce	uswsusp
Available in kernel	2.6.x	patch against 2.6.x	since 2.6.17
Kernel config option	CONFIG_HIBERNATION	CONFIG_TUXONICE	CONFIG_HIBERNATION
Principle author	Rafael Wysocki	Nigel Cunningham	Rafael Wysocki
PM subsystem required	none	none	none
Telling kernel at boot where to save image	resume=/dev/hda#	resume=<file:\|swap:>/dev/[node]<:sector> `If file & swap allocators are both compiled in, swap is the default.`
How to activate suspend	`echo -n disk > /sys/power/state`	`echo > /sys/power/tuxonice/do_suspend or echo disk > /sys/power/state if replacing swsusp is enabled.`	`Userspace program`
Telling kernel not to try and resume in case of a problem	`noresume`	`noresume`	`?`
Architecture support	i386, ppc, x86_64, ia64	i386, ppc, x86_64, ia64	i386, ppc, x86_64, ia64
Max. Image size	1/2 memory	See below	1/2 memory
Highmem support	Yes (up to 4GB)	Yes (up to 4GB)	Yes (up to 4GB)
Discontiguous memory support	Yes	Yes	Yes
SMP support	Yes	Yes	Yes
Preemption support	Yes	Yes	Yes
Compression	No	via cryptoapi - LZF recommended	Yes, with libraries
Encryption	No	by writing to dm-crypt partition	With libraries
Suspend-to-swapfile support	No	Yes	Yes?
Suspend-to-multiple swap partitions/files	No	Yes	No
Suspend-to-file support	No	Yes	No
Modular support	No	Yes (post 2.2.9)	No
Initrd support (needed for LVM/dm-crypt)	Yes	Yes	Required
UML support	No	No	No
Wake alarm support	No	Yes	No
Cluster support	No	In progress	No
Suspend-over-NFS support	No	No (also planned ;)	No
Auto swapon when starting to hibernate	No	Yes	No
Easy location of resume= values	No	Yes	No
Reconfigure without rebooting	No	Yes	No
Full mem. accounting, leak detection, failure path testing.	No	Yes	No
Expected compression ratio to avoid freeing too much mem.	No	Yes	No
Scripting support.	No	Yes	No
Keep image mode (For kiosks).	No	Yes	No
Mark resume attempted (sane default if resuming fails).	No	Yes	No
Multithreaded I/O	No	Yes	No
Readahead.	No	Yes	No
Cluster support.	No	In progress	No
Interactive debugging	No	Yes	No
Cancel hibernating via keyboard	No	Yes	Yes
Cancel resuming via keyboard	No	Yes	No
Switch poweroff method while hibernating	No	Yes	No
Checksummed image	No	Yes	No
Unloadable modules when not in use	No	Yes	No
Fuse support	No	Preliminary	No

TuxOnIce saves the image in two parts. The first part consists of the page cache, and is generally 70%+ of the memory in use. TuxOnIce saves this first, since it's not needed while saving the remainder. It then makes an atomic copy of the remainder, using the pages previously saved, and stores the atomic copy. Working in this way, TuxOnIce can normally save a full image of memory. Only if the page cache is smaller than 50% and there is no other free memory will TuxOnIce be unable to save a full image of memory.