Re: [PATCH] mm: respect pre-allocated storage mapping for memmap

[zhong jiang <zhongjiang@huawei.com>]

On 2017/1/17 18:25, Michal Hocko wrote:
> On Mon 16-01-17 21:38:05, zhongjiang wrote:
>> From: zhong jiang <zhongjiang@huawei.com>
>>
>> At present, we skip the reservation storage by the driver for
>> the zone_dvice. but the free pages set aside for the memmap is
>> ignored. And since the free pages is only used as the memmap,
>> so we can also skip the corresponding pages.
> I have really hard time to understand what this patch does and why it
> matters.  Could you please rephrase the changelog to state, the problem,
> how it affects users and what is the fix please?
>  
  Hi, Michal
 
  The patch maybe incorrect if free pages for memmap mapping is accouted for zone_device.
  I am just a little confusing about the implement.  it maybe simple and  stupid.

  first pfn for dev_mappage come from vmem_altmap_offset, and free pages reserved for
  memmap mapping need to be accounted. I do not know the meaning.

  Another issue is in sparse_remove_one_section.  A section belongs to  zone_device is not
  always need to consider the  map_offset. is it right ?  From pfn_first to end , that section
  should no need to consider the map_offet.

  Thanks
  zhongjiang
 
>> Signed-off-by: zhong jiang <zhongjiang@huawei.com>
>> ---
>>  mm/page_alloc.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index d604d25..51d8d03 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -5047,7 +5047,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>>  	 * memory
>>  	 */
>>  	if (altmap && start_pfn == altmap->base_pfn)
>> -		start_pfn += altmap->reserve;
>> +		start_pfn += vmem_altmap_offset(altmap);
>>  
>>  	for (pfn = start_pfn; pfn < end_pfn; pfn++) {
>>  		/*
>> -- 
>> 1.8.3.1
>>


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