Re: [RFC][PATCH] swsusp: support creating bigger images

[Nigel Cunningham]

Hi.

Sorry for the slow response - I only have internet access at work now. This is 
going to be a pattern for the next few weeks - I'm off work next week and.the 
week after I'll also be off apart from Monday and Tuesday (those are my last 
two days working for Cyclades - I then get my sweetheart and little one back, 
and we drive down to Victoria over the rest of the week).

On Sunday 30 April 2006 22:27, Rafael J. Wysocki wrote:
> Hi,
>
> On Wednesday 26 April 2006 02:49, Nigel Cunningham wrote:
> > On Wednesday 26 April 2006 08:43, Rafael J. Wysocki wrote:
> > > On Wednesday 26 April 2006 00:25, Pavel Machek wrote:
> > > > > > It does apply to all of the LRU pages. This is what I've been
> > > > > > doing for years now. The only corner case I've come across is
> > > > > > XFS. It still wants to write data even when there's nothing to do
> > > > > > and it's threads are frozen (IIRC - haven't looked at it for a
> > > > > > while). I got around that by freezing bdevs when freezing
> > > > > > processes.
> > > > >
> > > > > This means if we freeze bdevs, we'll be able to save all of the LRU
> > > > > pages, except for the pages mapped by the current task, without
> > > > > copying.  I think we can try to do this, but we'll need a patch to
> > > > > freeze bdevs for this purpose. ;-)
> > > >
> > > > ...adding more dependencies to how vm/blockdevs work. I'd say current
> > > > code is complex enough...
> > >
> > > Well, why don't we see the patch?  If it's too complex, we can just
> > > decide not to use it. :-)
> >
> > In Suspend2, I'm still using a different version of process.c to what you
> > guys have. In my version, I thaw kernelspace, then thaw bdevs, then thaw
> > userspace. The version below just thaws bdevs after thawing all
> > processes. I think that might need modification, but thought I'd post
> > this now so you can see how complicated or otherwise it is.
>
> IMHO it doesn't look so scary. :-)

:)

> > diff -ruN linux-2.6.17-rc2/kernel/power/process.c
> > bdev-freeze/kernel/power/process.c ---
> > linux-2.6.17-rc2/kernel/power/process.c	2006-04-19 14:27:36.000000000
> > +1000 +++ bdev-freeze/kernel/power/process.c	2006-04-26
> > 10:44:56.000000000 +1000 @@ -19,6 +19,56 @@
> >   */
> >  #define TIMEOUT	(20 * HZ)
> >
> > +struct frozen_fs
> > +{
> > +	struct list_head fsb_list;
> > +	struct super_block *sb;
> > +};
> > +
> > +LIST_HEAD(frozen_fs_list);
> > +
> > +void freezer_make_fses_rw(void)
> > +{
> > +	struct frozen_fs *fs, *next_fs;
> > +
> > +	list_for_each_entry_safe(fs, next_fs, &frozen_fs_list, fsb_list) {
> > +		thaw_bdev(fs->sb->s_bdev, fs->sb);
> > +
> > +		list_del(&fs->fsb_list);
> > +		kfree(fs);
> > +	}
> > +}
> > +
> > +/*
> > + * Done after userspace is frozen, so there should be no danger of
> > + * fses being unmounted while we're in here.
> > + */
> > +int freezer_make_fses_ro(void)
> > +{
> > +	struct frozen_fs *fs;
> > +	struct super_block *sb;
> > +
> > +	/* Generate the list */
> > +	list_for_each_entry(sb, &super_blocks, s_list) {
> > +		if (!sb->s_root || !sb->s_bdev ||
> > +		    (sb->s_frozen == SB_FREEZE_TRANS) ||
> > +		    (sb->s_flags & MS_RDONLY))
> > +			continue;
> > +
> > +		fs = kmalloc(sizeof(struct frozen_fs), GFP_ATOMIC);
>
> Shouldn't we check for kmalloc() failures here?

Good point. Just because I've never seen it fail, doesn't mean it can't :)

Before I roll a new version, what did you think splitting the thawing and 
thawing bdevs in the middle? I think it's the right thing (TM) to do :>

Nigel

> > +		fs->sb = sb;
> > +		list_add_tail(&fs->fsb_list, &frozen_fs_list);
> > +	};
> > +
> > +	/* Do the freezing in reverse order so filesystems dependant
> > +	 * upon others are frozen in the right order. (Eg loopback
> > +	 * on ext3). */
> > +	list_for_each_entry_reverse(fs, &frozen_fs_list, fsb_list)
> > +		freeze_bdev(fs->sb->s_bdev);
> > +
> > +	return 0;
> > +}
> > +
> >
> >  static inline int freezeable(struct task_struct * p)
> >  {
> > @@ -77,6 +127,7 @@
> >  	printk( "Stopping tasks: " );
> >  	start_time = jiffies;
> >  	user_frozen = 0;
> > +	bdevs_frozen = 0;
> >  	do {
> >  		nr_user = todo = 0;
> >  		read_lock(&tasklist_lock);
> > @@ -107,6 +158,10 @@
> >  			start_time = jiffies;
> >  		}
> >  		user_frozen = !nr_user;
> > +
> > +		if (user_frozen && !bdevs_frozen)
> > +			freezer_make_fses_ro();
> > +
> >  		yield();			/* Yield is okay here */
> >  		if (todo && time_after(jiffies, start_time + TIMEOUT))
> >  			break;
> > @@ -156,6 +211,8 @@
> >  			printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
> >  	} while_each_thread(g, p);
> >
> > +	freezer_make_fses_rw();
> > +
> >  	read_unlock(&tasklist_lock);
> >  	schedule();
> >  	printk( " done\n" );
>
> Greetings,
> Rafael

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