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

Zhang Zhen
2014-06-13T07:32:40Z

On 2014/6/12 15:07, David Rientjes wrote:
> On Thu, 12 Jun 2014, Zhang Zhen wrote:
>
>>>> % 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.
>>
>
> Ok, so you know specifically what sections_per_block is for your platform
> so you know exactly how many sections need to be added.
>
>> 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.
>>
>
> As I said, if the above returns errno at some point, it still can result
> in some sections being onlined. To be clear: if
> "echo 0x10000000 > /sys/devices/system/memory/probe" fails, the section
> starting at address 0x10000000 failed to be onlined for the reason
> specified by errno. If we follow your suggestion to specify how many
> sections to online, if
> "echo '0x10000000 16' > /sys/devices/system/memory/probe" fails, eight
> sections could have been successfully onlined at address 0x10000000 and
> then we encountered a failure (perhaps because the next sections were
> already onlined, we get an -EEXIST). We don't know what we successfully
> onlined.
>
> This could be mitigated, but there would have to be a convincing reason
> that this is better than using the currently functionally in a loop and
> properly handling your error codes.

Hi David,

I think you are right.

We had better to use the currently functionally in a loop if we need to add
several blocks.
In this way, we can get an errno in time if a block failed to be onlined.

Thanks for your comments. I got it.

>
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