Re: [PATCH v3 21/26] mm/page_alloc: implement FREETYPE_UNMAPPED allocations

["Brendan Jackman" <brendan.jackman@linux.dev>]

On Mon Aug 3, 2026 at 10:18 AM BST, Vlastimil Babka (SUSE) wrote:
>> +/*
>> + * Can pages of these two freetypes be combined into a single higher-order free
>> + * page?
>> + */
>> +static inline bool can_merge_freetypes(freetype_t a, freetype_t b)
>> +{
>> +	if (freetypes_equal(a, b))
>> +		return true;
>> +
>> +	if (!migratetype_is_mergeable(free_to_migratetype(a)) ||
>> +	    !migratetype_is_mergeable(free_to_migratetype(b)))
>> +		return false;
>> +
>> +	/*
>> +	 * Mustn't "just" merge pages with different freetype flags, changing
>> +	 * those requires updating pagetables.
>> +	 */
>> +	return freetype_flags(a) == freetype_flags(b);
>> +}
>> +
>>  /*
>>   * Freeing function for a buddy system allocator.
>>   *
>> @@ -1069,9 +1090,7 @@ static inline void __free_one_page(struct page *page,
>>  			buddy_ft = get_pfnblock_freetype(buddy, buddy_pfn);
>>  			buddy_mt = free_to_migratetype(buddy_ft);
>
> There's a comment above this that should probably be moved to
> can_merge_freetypes() as well?

True, thanks.