[swsusp fixes] Re: Linux 2.4.19pre5-ac3

[swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Pavel Machek]

Hi!

> > > Would love to but unless I mis-grepped it is not in the patch... Wanted
> > > to find out if it plays nice with ext3 now. :)
> > 
> > Its there ok
> 
> Including Documentation/swsusp.txt? Cos I can't see it in the patch.
> Just references to it.

Here it is, please apply.

Included is trivial fix to make it survive boot. I'm still
investigating why it crashes on suspend.
									Pavel

--- linux-ac.clean/Documentation/swsusp.txt	Tue Jan 29 12:16:13 2002
+++ linux-swsusp.24/Documentation/swsusp.txt	Sun Apr  7 11:42:03 2002
@@ -0,0 +1,168 @@
+From kernel/suspend.c:
+
+ * BIG FAT WARNING *********************************************************
+ *
+ * If you have unsupported (*) devices using DMA...
+ *				...say goodbye to your data.
+ *
+ * If you touch anything on disk between suspend and resume...
+ *				...kiss your data goodbye.
+ *
+ * If your disk driver does not support suspend... (IDE does)
+ *				...you'd better find out how to get along
+ *				   without your data.
+ *
+ * (*) pm interface support is needed to make it safe.
+
+You need to append resume=/dev/your_swap_partition to kernel command
+line. Then you suspend by echo 4 > /proc/acpi/sleep.
+
+[Notice. Rest docs is pretty outdated (see date!) It should be safe to
+use swsusp on ext3/reiserfs these days.]
+
+
+Article about goals and implementation of Software Suspend for Linux
+Author: Gábor Kuti
+Last revised: Jan 23rd, 2000
+
+Idea and goals to achieve
+
+Nowadays it is common in several laptops that they have a suspend button. It
+saves the state of the machine to a filesystem or to a partition and switches
+to standby mode. Later resuming the machine the saved state is loaded back to
+ram and the machine can continue its work. It has two real benefits. First we
+save ourselves the time machine goes down and later boots up, energy costs
+real high when running from batteries. The other gain is that we don't have to
+interrupt our programs so processes that are calculating something for a long
+time shouldn't need to be written interruptible.
+
+On desk machines the power saving function isn't as important as it is in
+laptops but we really may benefit from the second one. Nowadays the number of
+desk machines supporting suspend function in their APM is going up but there
+are (and there will still be for a long time) machines that don't even support
+APM of any kind. On the other hand it is reported that using APM's suspend
+some irqs (e.g. ATA disk irq) is lost and it is annoying for the user until
+the Linux kernel resets the device.
+
+So I started thinking about implementing Software Suspend which doesn't need
+any APM support and - since it uses pretty near only high-level routines - is
+supposed to be architecture independent code.
+
+Using the code
+
+The code is experimental right now - testers, extra eyes are welcome. To
+compile this support into the kernel, you need CONFIG_EXPERIMENTAL, 
+and then CONFIG_SOFTWARE_SUSPEND in menu General Setup to be  enabled. It
+cannot be used as a module and I don't think it will ever be needed.
+
+You have two ways to use this code. The first one is if you've compiled in
+sysrq support then you may press Sysrq-D to request suspend. The other way
+is with a patched SysVinit (my patch is against 2.76 and available at my
+home page). You might call 'swsusp' or 'shutdown -z <time>'.
+
+Either way it saves the state of the machine into active swaps and then
+reboots. By the next booting the kernel's resuming function is either triggered
+by swapon -a (which is ought to be in the very early stage of booting) or you
+may explicitly specify the swap partition/file to resume from with ``resume=''
+kernel option. If signature is found it loads and restores saved state. If the
+option ``noresume'' is specified as a boot parameter, it skips the resuming.
+Warning! Look at section ``Things to implement'' to see what isn't yet
+implemented.  Also I strongly suggest you to list all active swaps in
+/etc/fstab. Firstly because you don't have to specify anything to resume and
+secondly if you have more than one swap area you can't decide which one has the
+'root' signature. Also, it doesn't yet support ``embedded'' swapfiles, e.g. you
+have a dos partition mounted on /dos and also have a /dos/swapfile named
+swapfile..  I plan to add support to mount all necessary filesystems readonly.
+
+In the meantime while the system is suspended you should not touch any of the
+hardware!
+
+About the code
+Goals reached
+
+The code can be downloaded from
+http://falcon.sch.bme.hu/~seasons/linux/. It mainly works but there are still
+some of XXXs, TODOs, FIXMEs in the code which seem not to be too important. It
+should work all right except for the problems listed in ``Things to
+implement''. Notes about the code are really welcome.
+
+How the code works
+
+When suspending is triggered it immediately wakes up process bdflush. Bdflush
+checks whether we have anything in our run queue tq_bdflush. Since we queued up
+function do_software_suspend, it is called. Here we shrink everything including
+dcache, inodes, buffers and memory (here mainly processes are swapped out). We
+count how many pages we need to duplicate (we have to be atomical!) then we
+create an appropiate sized page directory. It will point to the original and
+the new (copied) address of the page. We get the free pages by
+__get_free_pages() but since it changes state we have to be able to track it
+later so it also flips in a bit in page's flags (a new Nosave flag). We
+duplicate pages and then mark them as used (so atomicity is ensured). After
+this we write out the image to swaps, do another sync and the machine may
+reboot. We also save registers to stack.
+
+By resuming an ``inverse'' method is executed. The image if exists is loaded,
+loadling is either triggered by ``swapon -a'' or ``resume='' kernel option.  We
+change our task to bdflush (it is needed because if we don't do this init does
+an oops when it is waken up later) and then pages are copied back to their
+original location. We restore registers, free previously allocated memory,
+activate memory context and task information. Here we should restore hardware
+state but even without this the machine is restored and processes are continued
+to work. I think hardware state should be restored by some list (using
+notify_chain) and probably by some userland program (run-parts?) for users'
+pleasure. Check out my patch at the same location for the sysvinit patch.
+
+WARNINGS!
+- Using swsusp on logging fs (e.g.reiserfs) could lead to pretty bad things:
+  mounting of reiserfs (even readonly!) means log is replayed, which 
+  means writes to filesystem. That could lead to pretty bad corruption.
+- It does not like pcmcia cards. And this is logical: pcmcia cards need cardmgr to be
+  initialized. they are not initialized during singleuser boot, but "resumed" kernel does
+  expect them to be initialized. That leads to armagedon. You should eject any pcmcia cards
+  before suspending.
+
+Things to implement
+- SMP support. I've done an SMP support but since I don't have access to a kind
+  of this one I cannot test it. Please SMP people test it.  .. Tested it,
+  doesn't work. Had no time to figure out why. There is some mess with
+  interrupts AFAIK..
+- We should only make a copy of data related to kernel segment, since any
+  process data won't be changed.
+- Should \#define ADDRESS go into linux/mm.h?
+- By copying pages back to their original position, copy_page caused General
+  Protection Fault. Why?
+- Hardware state restoring.  Now there's support for notifying via the notify
+  chain, event handlers are welcome. Some devices may have microcodes loaded
+  into them. We should have event handlers for them aswell.
+- We should support other architectures (There are really only some arch
+  related functions..)
+- We should also restore original state of swaps if the ``noresume'' kernel
+  option is specified.. Or do we need such a feature to save state for some
+  other time? Do we need some kind of ``several saved states''?  (Linux-HA
+  people?). There's been some discussion about checkpointing on linux-future.
+- Should make more sanity checks. Or are these enough?
+
+Not so important ideas for implementing
+
+- Should SIGSTOP_SUSPEND called SIGFREEZE? Or is it some kind of stealing
+  for Solaris?
+- If a real time process is running then don't suspend the machine.
+- Is there any sense in compressing the outwritten pages?
+- Support for power.conf file as in Solaris, autoshutdown, special
+  devicetypes support, maybe in sysctl.
+- Introduce timeout for SMP locking. But first locking ought to work :O
+- Pre-detect if we don't have enough swap space or free it instead of
+  calling panic.
+- Support for adding/removing hardware while suspended?
+- We should not free pages at the beginning so aggressively, most of them
+  go there anyway..
+- If X is active while suspending then by resuming calling svgatextmode
+  corrupts the virtual console of X.. (Maybe this has been fixed AFAIK).
+
+Any other idea you might have tell me!
+
+Contacting the author
+If you have any question or any patch that solves the above or detected
+problems please contact me at seasons@falcon.sch.bme.hu. I might delay
+answering, sorry about that.
+
--- linux-ac.clean/init/main.c	Sun Apr  7 10:55:13 2002
+++ linux-swsusp.24/init/main.c	Sun Apr  7 11:54:39 2002
@@ -522,15 +522,15 @@
 	tc_init();
 #endif
 
-	/* This has to be before mounting root, because even readonly mount of reiserfs would replay
-	   log corrupting stuff */
-	software_resume();
-
 	/* Networking initialization needs a process context */ 
 	sock_init();
 
 	start_context_thread();
 	do_initcalls();
+
+	/* This has to be before mounting root, because even readonly mount of reiserfs would replay
+	   log corrupting stuff */
+	software_resume();
 
 #ifdef CONFIG_IRDA
 	irda_proto_init();
--- linux-ac.clean/kernel/suspend.c	Sun Apr  7 10:55:13 2002
+++ linux-swsusp.24/kernel/suspend.c	Sun Apr  7 12:37:30 2002
@@ -32,20 +32,6 @@
  * More state savers are welcome. Especially for the scsi layer...
  *
  * For TODOs,FIXMEs also look in Documentation/swsusp.txt
- *
- * BIG FAT WARNING *********************************************************
- *
- * If you have unsupported (*) devices using DMA...
- *				...say goodbye to your data.
- *
- * If you touch anything on disk between suspend and resume...
- *				...kiss your data goodbye.
- *
- * If your disk driver does not support suspend... (IDE does)
- *				...you'd better find out how to get along
- *				   without your data.
- *
- * (*) pm interface support is needed to make it safe.
  */
 
 /*

-- 
(about SSSCA) "I don't say this lightly.  However, I really think that the U.S.
no longer is classifiable as a democracy, but rather as a plutocracy." --hpa

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Martin Knoblauch]

> [swsusp fixes] Re: Linux 2.4.19pre5-ac3
> 
> +
> +You have two ways to use this code. The first one is if you've compiled in
> +sysrq support then you may press Sysrq-D to request suspend. The other way
> +is with a patched SysVinit (my patch is against 2.76 and available at my
> +home page). You might call 'swsusp' or 'shutdown -z <time>'.
> +
> +Either way it saves the state of the machine into active swaps and then
> +reboots. By the next booting the kernel's resuming function is either triggered
> +by swapon -a (which is ought to be in the very early stage of booting) or you
> +may explicitly specify the swap partition/file to resume from with ``resume=''
> +kernel option. If signature is found it loads and restores saved state. If the

 Does it have to be an "active swap partition"? What about systems
without active swap, but space enough for a partition?

Martin
-- 
------------------------------------------------------------------
Martin Knoblauch         |    email:  Martin.Knoblauch@TeraPort.de
TeraPort GmbH            |    Phone:  +49-89-510857-309
C+ITS                    |    Fax:    +49-89-510857-111
http://www.teraport.de   |    Mobile: +49-170-4904759

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Pavel Machek]

Hi!

> > +
> > +You have two ways to use this code. The first one is if you've compiled in
> > +sysrq support then you may press Sysrq-D to request suspend. The other way
> > +is with a patched SysVinit (my patch is against 2.76 and available at my
> > +home page). You might call 'swsusp' or 'shutdown -z <time>'.
> > +
> > +Either way it saves the state of the machine into active swaps and then
> > +reboots. By the next booting the kernel's resuming function is either triggered
> > +by swapon -a (which is ought to be in the very early stage of booting) or you
> > +may explicitly specify the swap partition/file to resume from with ``resume=''
> > +kernel option. If signature is found it loads and restores saved state. If the
> 
>  Does it have to be an "active swap partition"? What about systems
> without active swap, but space enough for a partition?

There you just make it partition and then mkswap/swapon it. Or did I
misunderstand the question?
								Pavel
-- 
Casualities in World Trade Center: ~3k dead inside the building,
cryptography in U.S.A. and free speech in Czech Republic.

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Martin Knoblauch]

Pavel Machek wrote:
> 
> Hi!
> 
> > > +
> > > +You have two ways to use this code. The first one is if you've compiled in
> > > +sysrq support then you may press Sysrq-D to request suspend. The other way
> > > +is with a patched SysVinit (my patch is against 2.76 and available at my
> > > +home page). You might call 'swsusp' or 'shutdown -z <time>'.
> > > +
> > > +Either way it saves the state of the machine into active swaps and then
> > > +reboots. By the next booting the kernel's resuming function is either triggered
> > > +by swapon -a (which is ought to be in the very early stage of booting) or you
> > > +may explicitly specify the swap partition/file to resume from with ``resume=''
> > > +kernel option. If signature is found it loads and restores saved state. If the
> >
> >  Does it have to be an "active swap partition"? What about systems
> > without active swap, but space enough for a partition?
> 
> There you just make it partition and then mkswap/swapon it. Or did I
> misunderstand the question?
>                                                                 Pavel
Pavel,

 maybe I was unclear. For reasons of interactivity, I do not have any
swap enabled on my Notebook. The 320 MB are enough for my workload and I
am willing to accept the OOM Killer when I do really stupid things. If I
enable swap the (all of them to some degree :-) VM decides to swap out
"unused" processes. Most of them are desktop related and if I need them
the system responds sluggish. Therefore - no swap activated.

 My question was: can I have a system without active swap and still use
swsusp? Creating a swap/suspend partition of appropriate size is not a
problem. I just do not want to "swapon" it.

Martin
-- 
------------------------------------------------------------------
Martin Knoblauch         |    email:  Martin.Knoblauch@TeraPort.de
TeraPort GmbH            |    Phone:  +49-89-510857-309
C+ITS                    |    Fax:    +49-89-510857-111
http://www.teraport.de   |    Mobile: +49-170-4904759

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Pavel Machek]

Hi!

> > > > +
> > > > +You have two ways to use this code. The first one is if you've compiled in
> > > > +sysrq support then you may press Sysrq-D to request suspend. The other way
> > > > +is with a patched SysVinit (my patch is against 2.76 and available at my
> > > > +home page). You might call 'swsusp' or 'shutdown -z <time>'.
> > > > +
> > > > +Either way it saves the state of the machine into active swaps and then
> > > > +reboots. By the next booting the kernel's resuming function is either triggered
> > > > +by swapon -a (which is ought to be in the very early stage of booting) or you
> > > > +may explicitly specify the swap partition/file to resume from with ``resume=''
> > > > +kernel option. If signature is found it loads and restores saved state. If the
> > >
> > >  Does it have to be an "active swap partition"? What about systems
> > > without active swap, but space enough for a partition?
> > 
> > There you just make it partition and then mkswap/swapon it. Or did I
> > misunderstand the question?
> >                                                                 Pavel
> Pavel,
> 
>  maybe I was unclear. For reasons of interactivity, I do not have any
> swap enabled on my Notebook. The 320 MB are enough for my workload and I
> am willing to accept the OOM Killer when I do really stupid things. If I
> enable swap the (all of them to some degree :-) VM decides to swap out
> "unused" processes. Most of them are desktop related and if I need them
> the system responds sluggish. Therefore - no swap activated.
> 
>  My question was: can I have a system without active swap and still use
> swsusp? Creating a swap/suspend partition of appropriate size is not a
> problem. I just do not want to "swapon" it.

You need to swapon it. If you do not want to keep it swapped on,
there's no problem in

swapon /dev/swap
echo 4 > /proc/acpi/sleep
sleep 10
swapoff /dev/swap

									Pavel

-- 
Casualities in World Trade Center: ~3k dead inside the building,
cryptography in U.S.A. and free speech in Czech Republic.

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Martin Knoblauch]

Pavel Machek wrote:
> 
> >
> >  My question was: can I have a system without active swap and still use
> > swsusp? Creating a swap/suspend partition of appropriate size is not a
> > problem. I just do not want to "swapon" it.
> 
> You need to swapon it. If you do not want to keep it swapped on,
> there's no problem in
> 
> swapon /dev/swap
> echo 4 > /proc/acpi/sleep
> sleep 10
> swapoff /dev/swap
> 

 thanks. That is what I wanted to know. That basically means that I will
have to boot with a active swap device in order to get the resume
functionality - correct? And then I would do a "swapoff" late in the
boot process (maybe before starting the graphical crap :-).

Martin
-- 
------------------------------------------------------------------
Martin Knoblauch         |    email:  Martin.Knoblauch@TeraPort.de
TeraPort GmbH            |    Phone:  +49-89-510857-309
C+ITS                    |    Fax:    +49-89-510857-111
http://www.teraport.de   |    Mobile: +49-170-4904759

Re: [swsusp fixes] Re: Linux 2.4.19pre5-ac3

[Pavel Machek]

Hi!

> > >  My question was: can I have a system without active swap and still use
> > > swsusp? Creating a swap/suspend partition of appropriate size is not a
> > > problem. I just do not want to "swapon" it.
> > 
> > You need to swapon it. If you do not want to keep it swapped on,
> > there's no problem in
> > 
> > swapon /dev/swap
> > echo 4 > /proc/acpi/sleep
> > sleep 10
> > swapoff /dev/swap
> > 
> 
>  thanks. That is what I wanted to know. That basically means that I will
> have to boot with a active swap device in order to get the resume
> functionality - correct? And then I would do a "swapoff" late in the
> boot process (maybe before starting the graphical crap :-).

You do not need swapon during boot. swsusp no longer works like that
(it used to, but not now). swapon just before suspend is okay.
								Pavel
-- 
Casualities in World Trade Center: ~3k dead inside the building,
cryptography in U.S.A. and free speech in Czech Republic.