linux-kernel - Re: [Patch v4 09/12] memory-hotplug: remove page table of x86

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Message-ID: <50C19568.7080500@huawei.com>
Date:	Fri, 7 Dec 2012 15:06:16 +0800
From:	Jianguo Wu <wujianguo@...wei.com>
To:	Tang Chen <tangchen@...fujitsu.com>
CC:	Wen Congyang <wency@...fujitsu.com>, <x86@...nel.org>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-acpi@...r.kernel.org>,
	<linux-s390@...r.kernel.org>, <linux-sh@...r.kernel.org>,
	<linux-ia64@...r.kernel.org>, <cmetcalf@...era.com>,
	<sparclinux@...r.kernel.org>, David Rientjes <rientjes@...gle.com>,
	Jiang Liu <liuj97@...il.com>, Len Brown <len.brown@...el.com>,
	<benh@...nel.crashing.org>, <paulus@...ba.org>,
	Christoph Lameter <cl@...ux.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Jiang Liu <jiang.liu@...wei.com>
Subject: Re: [Patch v4 09/12] memory-hotplug: remove page table of x86_64
 architecture

On 2012/12/7 14:43, Tang Chen wrote:

> On 11/27/2012 06:00 PM, Wen Congyang wrote:
>> For hot removing memory, we sholud remove page table about the memory.
>> So the patch searches a page table about the removed memory, and clear
>> page table.
> 
> (snip)
> 
>> +void __meminit
>> +kernel_physical_mapping_remove(unsigned long start, unsigned long end)
>> +{
>> +    unsigned long next;
>> +    bool pgd_changed = false;
>> +
>> +    start = (unsigned long)__va(start);
>> +    end = (unsigned long)__va(end);
> 
> Hi Wu,
> 
> Here, you expect start and end are physical addresses. But in
> phys_xxx_remove() function, I think using virtual addresses is just
> fine. Functions like pmd_addr_end() and pud_index() only calculate
> an offset.
>

Hi Tang,

 

Virtual addresses will work fine, I used physical addresses in order to
keep consistent with phys_pud[pmd/pte]_init(), So I think we should keep this.

Thanks,
Jianguo Wu

> So, would you please tell me if we have to use physical addresses here ?
> 
> Thanks. :)
> 
>> +
>> +    for (; start<  end; start = next) {
>> +        pgd_t *pgd = pgd_offset_k(start);
>> +        pud_t *pud;
>> +
>> +        next = pgd_addr_end(start, end);
>> +
>> +        if (!pgd_present(*pgd))
>> +            continue;
>> +
>> +        pud = map_low_page((pud_t *)pgd_page_vaddr(*pgd));
>> +        phys_pud_remove(pud, __pa(start), __pa(next));
>> +        if (free_pud_table(pud, pgd))
>> +            pgd_changed = true;
>> +        unmap_low_page(pud);
>> +    }
>> +
>> +    if (pgd_changed)
>> +        sync_global_pgds(start, end - 1);
>> +
>> +    flush_tlb_all();
>> +}
>> +
>>   #ifdef CONFIG_MEMORY_HOTREMOVE
>>   int __ref arch_remove_memory(u64 start, u64 size)
>>   {
>> @@ -692,6 +921,8 @@ int __ref arch_remove_memory(u64 start, u64 size)
>>       ret = __remove_pages(zone, start_pfn, nr_pages);
>>       WARN_ON_ONCE(ret);
>>
>> +    kernel_physical_mapping_remove(start, start + size);
>> +
>>       return ret;
>>   }
>>   #endif
> 
> 
> 
> .
> 



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