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

David Hildenbrand
2019-06-05T21:50:52Z

On 05.06.19 23:22, Wei Yang wrote:
> 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?

Sure:

drivers/base/memory.c:memory_subsys_offline()

if (mem->section_count != sections_per_block)
return -EINVAL;

I would have expected such checks in the offline_pages() function instead.

--

Thanks,

David / dhildenb