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

[Nigel Cunningham <nigel@suspend2.net>]

Hi.

On Wednesday 26 April 2006 08:43, Rafael J. Wysocki wrote:
> Hi,
>
> 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.

Regards,

Nigel

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);
+		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" );


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