Subject: Re: [PATCH v3 07/11] mm/memory_hotplug: Create memory block devices after arch_add_memory()

From: Wei Yang <[email-masked]>
Date: Wed, 5 Jun 2019 21:22:49 +0000

On Wed, Jun 05, 2019 at 12:58:46PM +0200, David Hildenbrand wrote:
>On 05.06.19 10:58, David Hildenbrand wrote:
>>>> /*
>>>>  * For now, we have a linear search to go find the appropriate
>>>>  * memory_block corresponding to a particular phys_index. If
>>>> @@ -658,6 +670,11 @@ static int init_memory_block(struct memory_block **memory, int block_id,
>>>> 	unsigned long start_pfn;
>>>> 	int ret = 0;
>>>>
>>>> +	mem = find_memory_block_by_id(block_id, NULL);
>>>> +	if (mem) {
>>>> +		put_device(&mem->dev);
>>>> +		return -EEXIST;
>>>> +	}
>>>
>>> find_memory_block_by_id() is not that close to the main idea in this patch.
>>> Would it be better to split this part?
>> 
>> I played with that but didn't like the temporary results (e.g. having to
>> export find_memory_block_by_id()). I'll stick to this for now.
>> 
>>>
>>>> 	mem = kzalloc(sizeof(*mem), GFP_KERNEL);
>>>> 	if (!mem)
>>>> 		return -ENOMEM;
>>>> @@ -699,44 +716,53 @@ static int add_memory_block(int base_section_nr)
>>>> 	return 0;
>>>> }
>>>>
>>>> +static void unregister_memory(struct memory_block *memory)
>>>> +{
>>>> +	if (WARN_ON_ONCE(memory->dev.bus != &memory_subsys))
>>>> +		return;
>>>> +
>>>> +	/* drop the ref. we got via find_memory_block() */
>>>> +	put_device(&memory->dev);
>>>> +	device_unregister(&memory->dev);
>>>> +}
>>>> +
>>>> /*
>>>> - * need an interface for the VM to add new memory regions,
>>>> - * but without onlining it.
>>>> + * Create memory block devices for the given memory area. Start and size
>>>> + * have to be aligned to memory block granularity. Memory block devices
>>>> + * will be initialized as offline.
>>>>  */
>>>> -int hotplug_memory_register(int nid, struct mem_section *section)
>>>> +int create_memory_block_devices(unsigned long start, unsigned long size)
>>>> {
>>>> -	int block_id = base_memory_block_id(__section_nr(section));
>>>> -	int ret = 0;
>>>> +	const int start_block_id = pfn_to_block_id(PFN_DOWN(start));
>>>> +	int end_block_id = pfn_to_block_id(PFN_DOWN(start + size));
>>>> 	struct memory_block *mem;
>>>> +	unsigned long block_id;
>>>> +	int ret = 0;
>>>>
>>>> -	mutex_lock(&mem_sysfs_mutex);
>>>> +	if (WARN_ON_ONCE(!IS_ALIGNED(start, memory_block_size_bytes()) ||
>>>> +			 !IS_ALIGNED(size, memory_block_size_bytes())))
>>>> +		return -EINVAL;
>>>>
>>>> -	mem = find_memory_block(section);
>>>> -	if (mem) {
>>>> -		mem->section_count++;
>>>> -		put_device(&mem->dev);
>>>> -	} else {
>>>> +	mutex_lock(&mem_sysfs_mutex);
>>>> +	for (block_id = start_block_id; block_id != end_block_id; block_id++) {
>>>> 		ret = init_memory_block(&mem, block_id, MEM_OFFLINE);
>>>> 		if (ret)
>>>> -			goto out;
>>>> -		mem->section_count++;
>>>> +			break;
>>>> +		mem->section_count = sections_per_block;
>>>> +	}
>>>> +	if (ret) {
>>>> +		end_block_id = block_id;
>>>> +		for (block_id = start_block_id; block_id != end_block_id;
>>>> +		     block_id++) {
>>>> +			mem = find_memory_block_by_id(block_id, NULL);
>>>> +			mem->section_count = 0;
>>>> +			unregister_memory(mem);
>>>> +		}
>>>> 	}
>>>
>>> Would it be better to do this in reverse order?
>>>
>>> And unregister_memory() would free mem, so it is still necessary to set
>>> section_count to 0?
>> 
>> 1. I kept the existing behavior (setting it to 0) for now. I am planning
>> to eventually remove the section count completely (it could be
>> beneficial to detect removing of partially populated memory blocks).
>
>Correction: We already use it to block offlining of partially populated
>memory blocks \o/

Would you mind letting me know where we leverage this?

>
>> 
>> 2. Reverse order: We would have to start with "block_id - 1", I don't
>> like that better.
>> 
>> Thanks for having a look!
>> 
>
>
>-- 
>
>Thanks,
>
>David / dhildenb

-- 
Wei Yang
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