Re: [PATCH 2/2 v2, RFC] Driver core: Introduce offline/online callbacks for memory blocks

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Hi Rafael,

On 05/21/2013 07:15 PM, Rafael J. Wysocki wrote:
......
+		mem->state = to_state;
+		if (to_state == MEM_ONLINE)
+			mem->last_online = online_type;

Why do we need to remember last online type ?

And as far as I know, we can obtain which zone a page was in last time it
was onlined by check page->flags, just like online_pages() does. If we
use online_kernel or online_movable, the zone boundary will be
recalculated.
So we don't need to remember the last online type.

Seeing from your patch, I guess memory_subsys_online() can only handle
online and offline. So mem->last_online is used to remember what user has
done through the original way to trigger memory hot-remove, right ? And
when
user does it in this new way, it just does the same thing as user does last
time.

But I still think we don't need to remember it because if finally you call
online_pages(), it just does the same thing as last time by default.

online_pages()
{
	......
	if (online_type == ONLINE_KERNEL ......

	if (online_type == ONLINE_MOVABLE......

	zone = page_zone(pfn_to_page(pfn));

	/* Here, the page will be put into the zone which it belong to last
time. */

To be honest, it wasn't entirely clear to me that online_pages() would do the
same thing as last time by default.  Suppose, for example, that the previous
online_type was ONLINE_MOVABLE.  How online_pages() is supposed to know that
it should do the move_pfn_zone_right() if we don't tell it to do that?  Or
is that unnecessary, because it's already been done previously?

Yes, it is unnecessary. move_pfn_zone_right/left() will modify the zone related
bits in page->flags. But when the page is offline, the zone related bits in
page->flags will not change. So when it is online again, by dafault, it will
be in the zone which it was in last time.

......


I just thought of it. Maybe I missed something in your design. Please tell
me if I'm wrong.

Well, so what should be passed to __memory_block_change_state() in
memory_subsys_online()?  -1?

If you want to keep the last time status, you can pass ONLINE_KEEP.
Or -1 is all right.

Thanks. :)


Reviewed-by: Tang Chen<tangchen@xxxxxxxxxxxxxx>

Thanks. :)

Thanks for your comments,
Rafael



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