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

From: Tang Chen
Date: Wed May 22 2013 - 00:42:48 EST

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
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
user does it in this new way, it just does the same thing as user does last

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.

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,

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