Re: [PATCH v6 6/7] mm/memory_hotplug: Embed vmem_altmap details in memory block

[Aneesh Kumar K V <aneesh.kumar@linux.ibm.com>]

On 7/27/23 2:55 PM, Michal Hocko wrote:
> On Thu 27-07-23 13:32:31, Aneesh Kumar K.V wrote:
>> With memmap on memory, some architecture needs more details w.r.t altmap
>> such as base_pfn, end_pfn, etc to unmap vmemmap memory. Instead of
>> computing them again when we remove a memory block, embed vmem_altmap
>> details in struct memory_block if we are using memmap on memory block
>> feature.
>>
>> No functional change in this patch
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>  drivers/base/memory.c  | 25 +++++++++++-------
>>  include/linux/memory.h |  8 ++----
>>  mm/memory_hotplug.c    | 58 +++++++++++++++++++++++++++---------------
>>  3 files changed, 55 insertions(+), 36 deletions(-)
>>
>> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
>> index b456ac213610..57ed61212277 100644
>> --- a/drivers/base/memory.c
>> +++ b/drivers/base/memory.c
>> @@ -106,6 +106,7 @@ static void memory_block_release(struct device *dev)
>>  {
>>  	struct memory_block *mem = to_memory_block(dev);
>>  
>> +	WARN_ON(mem->altmap);
> 
> What is this supposed to catch? A comment would be handy so that we know
> what to look at should it ever trigger.
> 

I did add a comment where we clear the altmap in try_remove_memory(). I will also add
more details here.

+			 * Mark altmap NULL so that we can add a debug
+			 * check on memblock free.
 			 */

WARN_ON is an indication of memory leak because if we have mem->altmap != NULL
then the allocated altmap is not freed . It also indicate that memblock got freed
without going through the try_remove_memory(). 

>>  	kfree(mem);
>>  }


=aneesh