linux-kernel - Re: [PATCH v2 1/4] mm/memory-hotplug: fix lowmem count overflow when offline pages

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Message-ID: <51A21C63.4010606@gmail.com>
Date:	Sun, 26 May 2013 22:29:55 +0800
From:	Liu Jiang <liuj97@...il.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC:	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Tang Chen <tangchen@...fujitsu.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH v2 1/4] mm/memory-hotplug: fix lowmem count overflow when
 offline pages

On 05/26/2013 09:16 AM, KOSAKI Motohiro wrote:
>> ---
>>  mm/page_alloc.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 98cbdf6..23b921f 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -6140,6 +6140,8 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
>>  		list_del(&page->lru);
>>  		rmv_page_order(page);
>>  		zone->free_area[order].nr_free--;
>> +		if (PageHighMem(page))
>> +			totalhigh_pages -= 1 << order;
>>  		for (i = 0; i < (1 << order); i++)
>>  			SetPageReserved((page+i));
>>  		pfn += (1 << order);
> 
> memory hotplug don't support 32bit since it was born, at least, when the system has highmem. 
> Why can't we disable memory hotremove when 32bit at compile time?
Hi KOSAKI,
	Could you please help to give more information on the background
about why 32bit platforms with highmem can't support memory hot-removal?
We are trying to enable memory hot-removal on some 32bit platforms with
highmem, really appreciate your help here!
Thanks!
Gerry

> 
> 
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