Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation

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

On 7/11/23 11:51 AM, Huang, Ying wrote:
> "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> 
>> Add a new kconfig option that can be selected if we want to allow
>> pageblock alignment by reserving pages in the vmemmap altmap area.
>> This implies we will be reserving some pages for every memoryblock
>> This also allows the memmap on memory feature to be widely useful
>> with different memory block size values.
>>
>> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
>> ---
>>  mm/Kconfig          |  9 +++++++
>>  mm/memory_hotplug.c | 59 +++++++++++++++++++++++++++++++++++++--------
>>  2 files changed, 58 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 932349271e28..88a1472b2086 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -570,6 +570,15 @@ config MHP_MEMMAP_ON_MEMORY
>>  	depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
>>  	depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>>  
>> +config MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY
>> +       bool "Allow Reserving pages for page block aligment"
>> +       depends on MHP_MEMMAP_ON_MEMORY
>> +       help
>> +	This option allows memmap on memory feature to be more useful
>> +	with different memory block sizes. This is achieved by marking some pages
>> +	in each memory block as reserved so that we can get page-block alignment
>> +	for the remaining pages.
>> +
>>  endif # MEMORY_HOTPLUG
>>  
>>  config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 07c99b0cc371..f36aec1f7626 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1252,15 +1252,17 @@ static inline bool arch_supports_memmap_on_memory(unsigned long size)
>>  {
>>  	unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>>  	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>> -	unsigned long remaining_size = size - vmemmap_size;
>>  
>> -	return IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
>> -		IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
>> +	return IS_ALIGNED(vmemmap_size, PMD_SIZE);
>>  }
>>  #endif
>>  
>>  static bool mhp_supports_memmap_on_memory(unsigned long size)
>>  {
>> +	unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>> +	unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>> +	unsigned long remaining_size = size - vmemmap_size;
>> +
>>  	/*
>>  	 * Besides having arch support and the feature enabled at runtime, we
>>  	 * need a few more assumptions to hold true:
>> @@ -1287,9 +1289,30 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
>>  	 *       altmap as an alternative source of memory, and we do not exactly
>>  	 *       populate a single PMD.
>>  	 */
>> -	return mhp_memmap_on_memory() &&
>> -		size == memory_block_size_bytes() &&
>> -		arch_supports_memmap_on_memory(size);
>> +	if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
>> +		return false;
>> +	 /*
>> +	  * Without page reservation remaining pages should be pageblock aligned.
>> +	  */
>> +	if (!IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY) &&
>> +	    !IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT)))
>> +		return false;
>> +
>> +	return arch_supports_memmap_on_memory(size);
>> +}
>> +
>> +static inline unsigned long memory_block_align_base(unsigned long size)
>> +{
>> +	if (IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY)) {
>> +		unsigned long align;
>> +		unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>> +		unsigned long vmemmap_size;
>> +
>> +		vmemmap_size = (nr_vmemmap_pages * sizeof(struct page)) >> PAGE_SHIFT;
> 
> DIV_ROUND_UP()?
> 
>

yes. Will update.

		vmemmap_size = DIV_ROUND_UP(nr_vmemmap_pages * sizeof(struct page), PAGE_SIZE);

-aneesh