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

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Message-ID: <20251021012916.gkxh6cenjivwj455@master>
Date: Tue, 21 Oct 2025 01:29:16 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Wei Yang <richard.weiyang@...il.com>
Cc: Gregory Price <gourry@...rry.net>, linux-mm@...ck.org,
	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: Re: [RFC PATCH v2] page_alloc: allow migration of smaller hugepages
 during contig_alloc.

On Tue, Oct 21, 2025 at 01:25:33AM +0000, 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@...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);
>
>How about using folio_large_order(page_folio(page)) ?
>

Hmm... I see the discussion. Forget about it.

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

-- 
Wei Yang
Help you, Help me