Re: [PATCH v1] drivers/base/node.c: Simplify unregister_memory_block_under_nodes()

[David Hildenbrand <david@redhat.com>]

On 19.07.19 10:42, Michal Hocko wrote:
> On Thu 18-07-19 16:22:39, David Hildenbrand wrote:
>> We don't allow to offline memory block devices that belong to multiple
>> numa nodes. Therefore, such devices can never get removed. It is
>> sufficient to process a single node when removing the memory block.
>>
>> Remember for each memory block if it belongs to no, a single, or mixed
>> nodes, so we can use that information to skip unregistering or print a
>> warning (essentially a safety net to catch BUGs).
> 
> I do not really like NUMA_NO_NODE - 1 thing. This is yet another invalid
> node that is magic. Why should we even care? In other words why is this
> patch an improvement?

I mean we can of course go ahead and drop the "NUMA_NO_NODE - 1" thingy
from the patch. A memory block with multiple nodes would (as of now)
only indicate one of the nodes.

Then there is simply no way to WARN_ON_ONCE() in case unexpected things
would happen. (I mean it really shouldn't happen or we have a BUG
somewhere else)

Alternative: Add "bool mixed_nids;" to "struct memory block".

> 
>> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
>> Cc: Andrew Morton <akpm@linux-foundation.org>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Stephen Rothwell <sfr@canb.auug.org.au>
>> Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Oscar Salvador <osalvador@suse.de>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>> ---
>>  drivers/base/memory.c  |  1 +
>>  drivers/base/node.c    | 40 ++++++++++++++++------------------------
>>  include/linux/memory.h |  4 +++-
>>  3 files changed, 20 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>> index 20c39d1bcef8..154d5d4a0779 100644
>> --- a/drivers/base/memory.c
>> +++ b/drivers/base/memory.c
>> @@ -674,6 +674,7 @@ static int init_memory_block(struct memory_block **memory,
>>  	mem->state = state;
>>  	start_pfn = section_nr_to_pfn(mem->start_section_nr);
>>  	mem->phys_device = arch_get_memory_phys_device(start_pfn);
>> +	mem->nid = NUMA_NO_NODE;
>>  
>>  	ret = register_memory(mem);
>>  
>> diff --git a/drivers/base/node.c b/drivers/base/node.c
>> index 75b7e6f6535b..29d27b8d5fda 100644
>> --- a/drivers/base/node.c
>> +++ b/drivers/base/node.c
>> @@ -759,8 +759,6 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>>  	int ret, nid = *(int *)arg;
>>  	unsigned long pfn, sect_start_pfn, sect_end_pfn;
>>  
>> -	mem_blk->nid = nid;
>> -
>>  	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
>>  	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
>>  	sect_end_pfn += PAGES_PER_SECTION - 1;
>> @@ -789,6 +787,13 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>>  			if (page_nid != nid)
>>  				continue;
>>  		}
>> +
>> +		/* this memory block spans this node */
>> +		if (mem_blk->nid == NUMA_NO_NODE)
>> +			mem_blk->nid = nid;
>> +		else
>> +			mem_blk->nid = NUMA_NO_NODE - 1;
>> +
>>  		ret = sysfs_create_link_nowarn(&node_devices[nid]->dev.kobj,
>>  					&mem_blk->dev.kobj,
>>  					kobject_name(&mem_blk->dev.kobj));
>> @@ -804,32 +809,19 @@ static int register_mem_sect_under_node(struct memory_block *mem_blk,
>>  }
>>  
>>  /*
>> - * Unregister memory block device under all nodes that it spans.
>> - * Has to be called with mem_sysfs_mutex held (due to unlinked_nodes).
>> + * Unregister a memory block device under the node it spans. Memory blocks
>> + * with multiple nodes cannot be offlined and therefore also never be removed.
>>   */
>>  void unregister_memory_block_under_nodes(struct memory_block *mem_blk)
>>  {
>> -	unsigned long pfn, sect_start_pfn, sect_end_pfn;
>> -	static nodemask_t unlinked_nodes;
>> -
>> -	nodes_clear(unlinked_nodes);
>> -	sect_start_pfn = section_nr_to_pfn(mem_blk->start_section_nr);
>> -	sect_end_pfn = section_nr_to_pfn(mem_blk->end_section_nr);
>> -	for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) {
>> -		int nid;
>> +	if (mem_blk->nid == NUMA_NO_NODE ||
>> +	    WARN_ON_ONCE(mem_blk->nid == NUMA_NO_NODE - 1))
>> +		return;
>>  
>> -		nid = get_nid_for_pfn(pfn);
>> -		if (nid < 0)
>> -			continue;
>> -		if (!node_online(nid))
>> -			continue;
>> -		if (node_test_and_set(nid, unlinked_nodes))
>> -			continue;
>> -		sysfs_remove_link(&node_devices[nid]->dev.kobj,
>> -			 kobject_name(&mem_blk->dev.kobj));
>> -		sysfs_remove_link(&mem_blk->dev.kobj,
>> -			 kobject_name(&node_devices[nid]->dev.kobj));
>> -	}
>> +	sysfs_remove_link(&node_devices[mem_blk->nid]->dev.kobj,
>> +		 kobject_name(&mem_blk->dev.kobj));
>> +	sysfs_remove_link(&mem_blk->dev.kobj,
>> +		 kobject_name(&node_devices[mem_blk->nid]->dev.kobj));
>>  }
>>  
>>  int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn)
>> diff --git a/include/linux/memory.h b/include/linux/memory.h
>> index 02e633f3ede0..c91af10d5fb4 100644
>> --- a/include/linux/memory.h
>> +++ b/include/linux/memory.h
>> @@ -33,7 +33,9 @@ struct memory_block {
>>  	void *hw;			/* optional pointer to fw/hw data */
>>  	int (*phys_callback)(struct memory_block *);
>>  	struct device dev;
>> -	int nid;			/* NID for this memory block */
>> +	int nid;			/* NID for this memory block.
>> +					   - NUMA_NO_NODE: uninitialized
>> +					   - NUMA_NO_NODE - 1: mixed nodes */
>>  };
>>  
>>  int arch_get_memory_phys_device(unsigned long start_pfn);
>> -- 
>> 2.21.0
> 


-- 

Thanks,

David / dhildenb