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

[Tang Chen]

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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