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

Rafael J. Wysocki
2006-04-30T12:27:47Z

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?

> + 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