Subject: Re: [RFC PATCH 2/12] memory-hogplug : check memory offline in offline_pages

From: Yasuaki Ishimatsu <[email-masked]>
Date: Thu, 28 Jun 2012 15:51:52 +0900

Hi Kosaki-san,

2012/06/28 14:26, KOSAKI Motohiro wrote:
> On Wed, Jun 27, 2012 at 1:44 AM, Yasuaki Ishimatsu
> <[email-masked]> wrote:
>> When offline_pages() is called to offlined memory, the function fails since
>> all memory has been offlined. In this case, the function should succeed.
>> The patch adds the check function into offline_pages().
>
> I don't understand your point. I think following misoperation should
> fail. Otherwise
> administrator have no way to know their fault.
>
> $ echo offline > memoryN/state
> $ echo offline > memoryN/state
>
> In general, we don't like to ignore an error except the standard require it.

I understood the intention of previous mail (why the caller can't check it? ).
I'll move memory_is_offline() to caller side.

>>
>> CC: Len Brown <[email-masked]>
>> CC: Benjamin Herrenschmidt <[email-masked]>
>> CC: Paul Mackerras <[email-masked]>
>> CC: Christoph Lameter <[email-masked]>
>> Cc: Minchan Kim <[email-masked]>
>> CC: Andrew Morton <[email-masked]>
>> CC: KOSAKI Motohiro <[email-masked]>
>> CC: Wen Congyang <[email-masked]>
>> Signed-off-by: Yasuaki Ishimatsu <[email-masked]>
>>
>> ---
>>   drivers/base/memory.c  |   20 ++++++++++++++++++++
>>   include/linux/memory.h |    1 +
>>   mm/memory_hotplug.c    |    5 +++++
>>   3 files changed, 26 insertions(+)
>>
>> Index: linux-3.5-rc4/drivers/base/memory.c
>> ===================================================================
>> --- linux-3.5-rc4.orig/drivers/base/memory.c    2012-06-26 13:28:16.726211752 +0900
>> +++ linux-3.5-rc4/drivers/base/memory.c 2012-06-26 13:34:22.423639904 +0900
>> @@ -70,6 +70,26 @@ void unregister_memory_isolate_notifier(
>>   }
>>   EXPORT_SYMBOL(unregister_memory_isolate_notifier);
>>
>> +bool memory_is_offline(unsigned long start_pfn, unsigned long end_pfn)
>
> I dislike this function name. 'memory' is too vague to me.

O.K.
I retry to change the name of the function.

>
>
>> +{
>> +       struct memory_block *mem;
>> +       struct mem_section *section;
>> +       unsigned long pfn, section_nr;
>> +
>> +       for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
>> +               section_nr = pfn_to_section_nr(pfn);
>> +               section = __nr_to_section(section_nr);
>> +               mem = find_memory_block(section);
>
> This seems to have strong sparse dependency.

Thanks.
I will consider other CONFIG_.

Thanks.
Yasuaki Ishimatsu

> Hm, I wonder why memory-hotplug.c can enable when X86_64_ACPI_NUMA.
>
> # eventually, we can have this option just 'select SPARSEMEM'
> config MEMORY_HOTPLUG
> 	bool "Allow for memory hot-add"
> 	depends on SPARSEMEM || X86_64_ACPI_NUMA
>
>
>> +               if (!mem)
>> +                       continue;
>> +               if (mem->state == MEM_OFFLINE)
>> +                       continue;
>> +               return false;
>> +       }
>> +
>> +       return true;
>> +}
>> +
>>   /*
>>   * register_memory - Setup a sysfs device for a memory block
>>   */
>> Index: linux-3.5-rc4/include/linux/memory.h
>> ===================================================================
>> --- linux-3.5-rc4.orig/include/linux/memory.h   2012-06-25 04:53:04.000000000 +0900
>> +++ linux-3.5-rc4/include/linux/memory.h        2012-06-26 13:34:22.424639891 +0900
>> @@ -120,6 +120,7 @@ extern int memory_isolate_notify(unsigne
>>   extern struct memory_block *find_memory_block_hinted(struct mem_section *,
>>                                                         struct memory_block *);
>>   extern struct memory_block *find_memory_block(struct mem_section *);
>> +extern bool memory_is_offline(unsigned long start_pfn, unsigned long end_pfn);
>>   #define CONFIG_MEM_BLOCK_SIZE  (PAGES_PER_SECTION<<PAGE_SHIFT)
>>   enum mem_add_context { BOOT, HOTPLUG };
>>   #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
>> Index: linux-3.5-rc4/mm/memory_hotplug.c
>> ===================================================================
>> --- linux-3.5-rc4.orig/mm/memory_hotplug.c      2012-06-26 13:28:16.743211538 +0900
>> +++ linux-3.5-rc4/mm/memory_hotplug.c   2012-06-26 13:48:38.264940468 +0900
>> @@ -887,6 +887,11 @@ static int __ref offline_pages(unsigned
>>
>>         lock_memory_hotplug();
>>
>> +       if (memory_is_offline(start_pfn, end_pfn)) {
>> +               ret = 0;
>> +               goto out;
>> +       }
>> +
>>         zone = page_zone(pfn_to_page(start_pfn));
>>         node = zone_to_nid(zone);
>>         nr_pages = end_pfn - start_pfn;
>>
>> --
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