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

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Date:	Tue, 21 May 2013 14:37:53 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Toshi Kani <toshi.kani@...com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	isimatu.yasuaki@...fujitsu.com,
	vasilis.liaskovitis@...fitbricks.com, Len Brown <lenb@...nel.org>,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/2 v2, RFC] Driver core: Introduce offline/online callbacks
 for memory blocks

Hi Rafael,

Please see below.

On 05/04/2013 07:21 PM, Rafael J. Wysocki wrote:
......
>   static BLOCKING_NOTIFIER_HEAD(memory_chain);
> @@ -278,33 +283,64 @@ static int __memory_block_change_state(s
>   {
>   	int ret = 0;
>
> -	if (mem->state != from_state_req) {
> -		ret = -EINVAL;
> -		goto out;
> -	}
> +	if (mem->state != from_state_req)
> +		return -EINVAL;
>
>   	if (to_state == MEM_OFFLINE)
>   		mem->state = MEM_GOING_OFFLINE;
>
>   	ret = memory_block_action(mem->start_section_nr, to_state, online_type);
> -
>   	if (ret) {
>   		mem->state = from_state_req;
> -		goto out;
> +	} else {
> +		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. */

	......
}

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

Reviewed-by: Tang Chen <tangchen@...fujitsu.com>

Thanks. :)

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