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

Wei Yang
2019-06-05T21:22:49Z

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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