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

David Hildenbrand
2019-06-05T08:58:26Z

>> /*
>> * 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).

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