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

[Wei Yang <richard.weiyang@gmail.com>]

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)) ?

>+			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
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