Re: [RFC PATCH 3/4] mm/hotplug: make __add_pages() iterate on memory_block and split __add_section()

[Wei Yang <richard.weiyang@gmail.com>]

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On Mon, Jun 26, 2017 at 12:50:14AM -0700, John Hubbard wrote:
>On 06/24/2017 07:52 PM, Wei Yang wrote:
>> Memory hotplug unit is memory_block which contains one or several
>> mem_section. The current logic is iterating on each mem_section and add or
>> adjust the memory_block every time.
>> 
>> This patch makes the __add_pages() iterate on memory_block and split
>> __add_section() to two functions: __add_section() and __add_memory_block().
>> 
>> The first one would take care of each section data and the second one would
>> register the memory_block at once, which makes the function more clear and
>> natural.
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> ---
>>  drivers/base/memory.c | 17 +++++------------
>>  mm/memory_hotplug.c   | 27 +++++++++++++++++----------
>>  2 files changed, 22 insertions(+), 22 deletions(-)
>> 
>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>> index b54cfe9cd98b..468e5ad1bc87 100644
>> --- a/drivers/base/memory.c
>> +++ b/drivers/base/memory.c
>> @@ -705,19 +705,12 @@ int register_new_memory(int nid, struct mem_section *section)
>>  
>>  	mutex_lock(&mem_sysfs_mutex);
>>  
>> -	mem = find_memory_block(section);
>> -	if (mem) {
>> -		mem->section_count++;
>> -		put_device(&mem->dev);
>> -	} else {
>> -		ret = init_memory_block(&mem, section, MEM_OFFLINE);
>> -		if (ret)
>> -			goto out;
>> -		mem->section_count++;
>> -	}
>> +	ret = init_memory_block(&mem, section, MEM_OFFLINE);
>> +	if (ret)
>> +		goto out;
>> +	mem->section_count = sections_per_block;
>
>Hi Wei,
>
>Things have changed...the register_new_memory() routine is accepting a single section,
>but instead of registering just that section, it is registering a containing block.
>(That works, because apparently the approach is to make sections_per_block == 1,
>and eventually kill sections, if I am reading all this correctly.)
>

The original function is a little confusing. Actually it tries to register a
memory_block while it register it for several times, on each present
mem_section actually.

This change here will register the whole memory_block at once.

You would see in next patch it will accept the start section number instead of
a section, while maybe more easy to understand it.

BTW, I don't get your point on kill sections when sections_per_block == The
original function is a little confusing. Actually it tries to register a
memory_block while it register it for several times, on each present
mem_section actually.

This change here will register the whole memory_block at once.

You would see in next patch it will accept the start section number instead of
a section, while maybe more easy to understand it.

BTW, I don't get your point on kill sections when sections_per_block == 1.
Would you rephrase this?

>So, how about this: let's add a line to the function comment: 
>
>* Register an entire memory_block.
>

May look good, let me have a try.

>That makes it clearer that we're dealing in blocks, even though the memsection*
>argument is passed in.
>
>>  
>> -	if (mem->section_count == sections_per_block)
>> -		ret = register_mem_sect_under_node(mem, nid);
>> +	ret = register_mem_sect_under_node(mem, nid);
>>  out:
>>  	mutex_unlock(&mem_sysfs_mutex);
>>  	return ret;
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index a79a83ec965f..14a08b980b59 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -302,8 +302,7 @@ void __init register_page_bootmem_info_node(struct pglist_data *pgdat)
>>  }
>>  #endif /* CONFIG_HAVE_BOOTMEM_INFO_NODE */
>>  
>> -static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
>> -		bool want_memblock)
>> +static int __meminit __add_section(int nid, unsigned long phys_start_pfn)
>>  {
>>  	int ret;
>>  	int i;
>> @@ -332,6 +331,18 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
>>  		SetPageReserved(page);
>>  	}
>>  
>> +	return 0;
>> +}
>> +
>> +static int __meminit __add_memory_block(int nid, unsigned long phys_start_pfn,
>> +		bool want_memblock)
>> +{
>> +	int ret;
>> +
>> +	ret = __add_section(nid, phys_start_pfn);
>> +	if (ret)
>> +		return ret;
>> +
>>  	if (!want_memblock)
>>  		return 0;
>>  
>> @@ -347,15 +358,10 @@ static int __meminit __add_section(int nid, unsigned long phys_start_pfn,
>>  int __ref __add_pages(int nid, unsigned long phys_start_pfn,
>>  			unsigned long nr_pages, bool want_memblock)
>>  {
>> -	unsigned long i;
>> +	unsigned long pfn;
>>  	int err = 0;
>> -	int start_sec, end_sec;
>>  	struct vmem_altmap *altmap;
>>  
>> -	/* during initialize mem_map, align hot-added range to section */
>> -	start_sec = pfn_to_section_nr(phys_start_pfn);
>> -	end_sec = pfn_to_section_nr(phys_start_pfn + nr_pages - 1);
>> -
>>  	altmap = to_vmem_altmap((unsigned long) pfn_to_page(phys_start_pfn));
>>  	if (altmap) {
>>  		/*
>> @@ -370,8 +376,9 @@ int __ref __add_pages(int nid, unsigned long phys_start_pfn,
>>  		altmap->alloc = 0;
>>  	}
>>  
>> -	for (i = start_sec; i <= end_sec; i++) {
>> -		err = __add_section(nid, section_nr_to_pfn(i), want_memblock);
>> +	for (pfn; pfn < phys_start_pfn + nr_pages;
>> +			pfn += sections_per_block * PAGES_PER_SECTION) {
>

yep

>A pages_per_block variable would be nice here, too.
>
>thanks,
>john h
>
>> +		err = __add_memory_block(nid, pfn, want_memblock);
>>  
>>  		/*
>>  		 * EEXIST is finally dealt with by ioresource collision
>> 

-- 
Wei Yang
Help you, Help me

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