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Subject: Re: [PATCH v3 07/11] mm/memory_hotplug: Create memory block devices
 after arch_add_memory()
From:   David Hildenbrand <david@redhat.com>
To:     Wei Yang <richard.weiyang@gmail.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linux-ia64@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
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        linux-arm-kernel@lists.infradead.org, akpm@linux-foundation.org,
        Dan Williams <dan.j.williams@intel.com>,
        Igor Mammedov <imammedo@redhat.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        "mike.travis@hpe.com" <mike.travis@hpe.com>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Banman <andrew.banman@hpe.com>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>,
        Pavel Tatashin <pasha.tatashin@soleen.com>,
        Qian Cai <cai@lca.pw>, Arun KS <arunks@codeaurora.org>,
        Mathieu Malaterre <malat@debian.org>
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Organization: Red Hat GmbH
Message-ID: <9a1d282f-8dd9-a48b-cc96-f9afaa435c62@redhat.com>
Date:   Wed, 5 Jun 2019 12:58:46 +0200
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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/

> 
> 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