linux-kernel - Re: [PATCH 2/3] memory-hotplug: more general validation of zone during online

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Date:	Wed, 11 May 2016 08:17:41 -0700 (PDT)
From:	Yasuaki Ishimatsu <yasu.isimatu@...il.com>
To:	Reza Arbab <arbab@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Daniel Kiper <daniel.kiper@...cle.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Tang Chen <tangchen@...fujitsu.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Vrabel <david.vrabel@...rix.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Banman <abanman@....com>,
	Chen Yucong <slaoub@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Subject: Re: [PATCH 2/3] memory-hotplug: more general validation of zone
 during online


On Tue, 10 May 2016 15:39:43 -0500
Reza Arbab <arbab@...ux.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@...ux.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