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Date: Wed, 11 May 2016 08:17:41 -0700 (PDT)
From: Yasuaki Ishimatsu <yasu.isimatu@gmail.com>
To: Reza Arbab <arbab@linux.vnet.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Daniel Kiper <daniel.kiper@oracle.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Vlastimil Babka <vbabka@suse.cz>, Tang Chen <tangchen@cn.fujitsu.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        David Vrabel <david.vrabel@citrix.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        David Rientjes <rientjes@google.com>, Andrew Banman <abanman@sgi.com>,
        Chen Yucong <slaoub@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Subject: Re: [PATCH 2/3] memory-hotplug: more general validation of zone
 during online
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On Tue, 10 May 2016 15:39:43 -0500
Reza Arbab <arbab@linux.vnet.ibm.com> wrote:

> On Tue, May 10, 2016 at 11:08:56AM -0700, Yasuaki Ishimatsu wrote:
> >On Mon,  9 May 2016 12:53:38 -0500
> >Reza Arbab <arbab@linux.vnet.ibm.com> wrote:
> >> * If X is lower than Y, the onlined memory must lie at the end of X.
> >> * If X is higher than Y, the onlined memory must lie at the start of X.
> >
> >If memory address has hole, memory address gets uncotinuous. Then memory
> >cannot be changed the zone by above the two conditions. So the conditions
> >shouold be removed.
> 
> I don't understand what you mean by this. Could you give an example?

> +int zone_can_shift(unsigned long pfn, unsigned long nr_pages,
> +		   enum zone_type target)
> +{
<snip>
> +	if (idx < target) {
> +		/* pages must be at end of current zone */
> +		if (pfn + nr_pages != zone_end_pfn(zone))
> +			return 0;
<snip>
> +	if (target < idx) {
> +		/* pages must be at beginning of current zone */
> +		if (pfn != zone->zone_start_pfn)
> +			return 0;

According your patch, memory address must be continuous for changing zone.
So if memory address is uncontinuous as follows, memory address 0x180000000-0x1FFFFFFFF
can be changed from ZONE_NORMAL to ZONE_MOVABLE. But memory address 0x80000000-0xFFFFFFFF
can not be changed from ZONE_NORMAL to ZONE_MOVABLE since it does not meet
above condition.

Memory address
  0x80000000 -  0xFFFFFFFF
 0x180000000 - 0x1FFFFFFFF

Thanks,
Yasuaki Ishimatsu