linux-kernel - Re: Proposal to realize hot-add *several sections one time*

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Date:	Thu, 12 Jun 2014 10:41:23 +0800
From:	Zhang Zhen <zhenzhang.zhang@...wei.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	<gregkh@...uxfoundation.org>, <laijs@...fujitsu.com>,
	<sjenning@...ux.vnet.ibm.com>, <linux-kernel@...r.kernel.org>,
	<linux-mm@...ck.org>, Wang Nan <wangnan0@...wei.com>
Subject: Re: Proposal to realize hot-add *several sections one time*

On 2014/6/12 6:08, David Rientjes wrote:
> On Wed, 11 Jun 2014, Zhang Zhen wrote:
> 
>> Hi,
>>
>> Now we can hot-add memory by
>>
>> % echo start_address_of_new_memory > /sys/devices/system/memory/probe
>>
>> Then, [start_address_of_new_memory, start_address_of_new_memory +
>> memory_block_size] memory range is hot-added.
>>
>> But we can only hot-add *one section one time* by this way.
>> Whether we can add an argument on behalf of the count of the sections to add ?
>> So we can can hot-add *several sections one time*. Just like:
>>
> 
> Not necessarily true, it depends on sections_per_block.  Don't believe 
> Documentation/memory-hotplug.txt that suggests this is only for powerpc, 
> x86 and sh allow this interface as well.
> 
>> % echo start_address_of_new_memory count_of_sections > /sys/devices/system/memory/probe
>>
>> Then, [start_address_of_new_memory, start_address_of_new_memory +
>> count_of_sections * memory_block_size] memory range is hot-added.
>>
>> If this proposal is reasonable, i will send a patch to realize it.
>>
> 
> The problem is knowing how much memory is being onlined so that you can 
> definitively determine what count_of_sections should be.  The number of 
> pages per memory section depends on PAGE_SIZE and SECTION_SIZE_BITS which 
> differ depending on the architectures that support this interface.  So if 
> you support count_of_sections, it would return errno even though you have 
> onlined some sections.
> 
Hum, sorry.
My expression is not right. The count of sections one time hot-added
depends on sections_per_block.

Now we are porting the memory-hotplug to arm.
But we can only hot-add *fixed number of sections one time* on particular architecture.

Whether we can add an argument on behalf of the count of the blocks to add ?

% echo start_address_of_new_memory count_of_blocks > /sys/devices/system/memory/probe

Then, [start_address_of_new_memory, start_address_of_new_memory + count_of_blocks * memory_block_size]
memory range is hot-added.

So user don't need execute several times of echo when they want to hot add multi-block size memory.

Any comments are welcome.

Best regards!
> 


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