[RFC][PATCH -mm][Experimental] suspend: Do not freeze md_threads

[RFC][PATCH -mm][Experimental] suspend: Do not freeze md_threads

[Rafael J. Wysocki]

Hi,

If there's a swap file on a software RAID, it should be possible to use this
file for saving the swsusp's suspend image.  Also, this file should be
available to the memory management subsystem when memory is being freed before
the suspend image is created.

For the above reasons it seems that md_threads should not be frozen during
the suspend and the appended patch makes this happen, but then there is the
question if they don't cause any data to be written to disks after the
suspend image has been created, provided that all filesystems are frozen
at that time.

Please advise.

Greetings,
Rafael


Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
---
 drivers/md/md.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6.19-rc4-mm2/drivers/md/md.c
===================================================================
--- linux-2.6.19-rc4-mm2.orig/drivers/md/md.c	2006-11-02 20:51:51.000000000 +0100
+++ linux-2.6.19-rc4-mm2/drivers/md/md.c	2006-11-02 23:25:59.000000000 +0100
@@ -4489,6 +4489,7 @@ static int md_thread(void * arg)
 	 * many dirty RAID5 blocks.
 	 */
 
+	current->flags |= PF_NOFREEZE;
 	allow_signal(SIGKILL);
 	while (!kthread_should_stop()) {
 
@@ -4505,7 +4506,6 @@ static int md_thread(void * arg)
 			 test_bit(THREAD_WAKEUP, &thread->flags)
 			 || kthread_should_stop(),
 			 thread->timeout);
-		try_to_freeze();
 
 		clear_bit(THREAD_WAKEUP, &thread->flags);
 

Re: [RFC][PATCH -mm][Experimental] suspend: Do not freeze md_threads

[Pavel Machek]

Hi!

> If there's a swap file on a software RAID, it should be possible to use this
> file for saving the swsusp's suspend image.  Also, this file should be
> available to the memory management subsystem when memory is being freed before
> the suspend image is created.
> 
> For the above reasons it seems that md_threads should not be frozen during
> the suspend and the appended patch makes this happen, but then there is the
> question if they don't cause any data to be written to disks after the
> suspend image has been created, provided that all filesystems are frozen
> at that time.

Looks okay to me. It would be nice to have someone (Ingo? Neil?) try
to suspend to swap on md......
								Pavel

> Please advise.
> 
> Greetings,
> Rafael
> 
> 
> Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
> ---
>  drivers/md/md.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: linux-2.6.19-rc4-mm2/drivers/md/md.c
> ===================================================================
> --- linux-2.6.19-rc4-mm2.orig/drivers/md/md.c	2006-11-02 20:51:51.000000000 +0100
> +++ linux-2.6.19-rc4-mm2/drivers/md/md.c	2006-11-02 23:25:59.000000000 +0100
> @@ -4489,6 +4489,7 @@ static int md_thread(void * arg)
>  	 * many dirty RAID5 blocks.
>  	 */
>  
> +	current->flags |= PF_NOFREEZE;
>  	allow_signal(SIGKILL);
>  	while (!kthread_should_stop()) {
>  
> @@ -4505,7 +4506,6 @@ static int md_thread(void * arg)
>  			 test_bit(THREAD_WAKEUP, &thread->flags)
>  			 || kthread_should_stop(),
>  			 thread->timeout);
> -		try_to_freeze();
>  
>  		clear_bit(THREAD_WAKEUP, &thread->flags);
>  

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

Re: [RFC][PATCH -mm][Experimental] suspend: Do not freeze md_threads

[Neil Brown]

On Sunday November 5, pavel@ucw.cz wrote:
> Hi!
> 
> > If there's a swap file on a software RAID, it should be possible to use this
> > file for saving the swsusp's suspend image.  Also, this file should be
> > available to the memory management subsystem when memory is being freed before
> > the suspend image is created.
> > 
> > For the above reasons it seems that md_threads should not be frozen during
> > the suspend and the appended patch makes this happen, but then there is the
> > question if they don't cause any data to be written to disks after the
> > suspend image has been created, provided that all filesystems are frozen
> > at that time.
> 
> Looks okay to me. It would be nice to have someone (Ingo? Neil?) try
> to suspend to swap on md......

Yes... suspending to swap-on-md would probably be fairly easy.
Resuming from that same swap might be a bit more of a challenge.
If only I had more time...

but the patch looks good to me.  I'll see that it gets applied.
Thanks,

NeilBrown

Re: [RFC][PATCH -mm][Experimental] suspend: Do not freeze md_threads

[Pavel Machek]

Hi!

> > > If there's a swap file on a software RAID, it should be possible to use this
> > > file for saving the swsusp's suspend image.  Also, this file should be
> > > available to the memory management subsystem when memory is being freed before
> > > the suspend image is created.
> > > 
> > > For the above reasons it seems that md_threads should not be frozen during
> > > the suspend and the appended patch makes this happen, but then there is the
> > > question if they don't cause any data to be written to disks after the
> > > suspend image has been created, provided that all filesystems are frozen
> > > at that time.
> > 
> > Looks okay to me. It would be nice to have someone (Ingo? Neil?) try
> > to suspend to swap on md......
> 
> Yes... suspending to swap-on-md would probably be fairly easy.
> Resuming from that same swap might be a bit more of a challenge.
> If only I had more time...

With uswsusp (scheduled for 10.2), it should be fairly easy, too. I
guess we shall just get Andrea to try it :-).
							Pavel 
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html