linux-kernel - [RFC PATCH v2] page_alloc: allow migration of smaller hugepages during contig

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Message-ID: <20251020210816.1089910-1-gourry@gourry.net>
Date: Mon, 20 Oct 2025 17:08:16 -0400
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
Cc: linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	akpm@...ux-foundation.org,
	vbabka@...e.cz,
	surenb@...gle.com,
	mhocko@...e.com,
	jackmanb@...gle.com,
	hannes@...xchg.org,
	ziy@...dia.com,
	David Hildenbrand <david@...hat.com>
Subject: [RFC PATCH v2] page_alloc: allow migration of smaller hugepages during contig_alloc.

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
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@...hat.com>
Signed-off-by: Gregory Price <gourry@...rry.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);
+			if ((order >= MAX_PAGE_ORDER) ||
+			    (nr_pages < (1 << order)))
+				return false;
+		}
 	}
 	return true;
 }
-- 
2.51.0