Re: [RFC PATCH v2] page_alloc: allow migration of smaller hugepages during contig_alloc.

[Zi Yan <ziy@nvidia.com>]

On 20 Oct 2025, at 21:25, Wei Yang wrote:

> On Mon, Oct 20, 2025 at 05:08:16PM -0400, Gregory Price wrote:
>> We presently skip regions with hugepages entirely when trying to do
>> contiguous page allocation.  Instead, if hugepage migration is enabled,
>> consider regions with hugepages smaller than the requested allocation.
>>
>> Compaction `isolate_migrate_pages_block()` already expects requests
>
> isolate_migratepages_block() ?
>
>> with hugepages to originate from alloc_contig, and hugetlb code also
>> does a migratable check when isolating in `folio_isolate_hugetlb()`.
>>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Gregory Price <gourry@gourry.net>
>> ---
>> mm/page_alloc.c | 15 +++++++++++++--
>> 1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index 600d9e981c23..da2e65bf63e3 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -7048,8 +7048,19 @@ static bool pfn_range_valid_contig(struct zone *z, unsigned long start_pfn,
>> 		if (PageReserved(page))
>> 			return false;
>>
>> -		if (PageHuge(page))
>> -			return false;
>> +		if (PageHuge(page)) {
>> +			unsigned int order;
>> +
>> +			if (!IS_ENABLED(CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION))
>> +				return false;
>> +
>> +			/* Don't consider moving same size/larger pages */
>> +			page = compound_head(page);
>> +			order = compound_order(page);
>
> How about using folio_large_order(page_folio(page)) ?

See the discussion at https://lore.kernel.org/linux-mm/609E7E01-33A6-4931-AC89-1F4B2944FB64@nvidia.com/ about reading folio order without locking.

>
>> +			if ((order >= MAX_PAGE_ORDER) ||
>> +			    (nr_pages < (1 << order)))
>> +				return false;
>> +		}
>> 	}
>> 	return true;
>> }
>> -- 
>> 2.51.0
>>
>
> Generally LGTM
>
> Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
>
> -- 
> Wei Yang
> Help you, Help me


--
Best Regards,
Yan, Zi