linux-kernel - Re: [v4 06/15] mm/migrate_device: implement THP migration of zone device pages

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Message-ID: <20250911080404.r6vqlhyi7qyjutij@master>
Date: Thu, 11 Sep 2025 08:04:04 +0000
From: Wei Yang <richard.weiyang@...il.com>
To: Balbir Singh <balbirs@...dia.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, damon@...ts.linux.dev,
	dri-devel@...ts.freedesktop.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>, Zi Yan <ziy@...dia.com>,
	Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
	Byungchul Park <byungchul@...com>,
	Gregory Price <gourry@...rry.net>,
	Ying Huang <ying.huang@...ux.alibaba.com>,
	Alistair Popple <apopple@...dia.com>,
	Oscar Salvador <osalvador@...e.de>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Nico Pache <npache@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>, Barry Song <baohua@...nel.org>,
	Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
	Ralph Campbell <rcampbell@...dia.com>,
	Mika Penttilä <mpenttil@...hat.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Francois Dugast <francois.dugast@...el.com>
Subject: Re: [v4 06/15] mm/migrate_device: implement THP migration of zone
 device pages

On Wed, Sep 03, 2025 at 11:18:51AM +1000, Balbir Singh wrote:
[...]
>@@ -836,15 +1107,47 @@ static void __migrate_device_pages(unsigned long *src_pfns,
> 					migrate->pgmap_owner);
> 				mmu_notifier_invalidate_range_start(&range);
> 			}
>-			migrate_vma_insert_page(migrate, addr, newpage,
>+
>+			if ((src_pfns[i] & MIGRATE_PFN_COMPOUND) &&
>+				(!(dst_pfns[i] & MIGRATE_PFN_COMPOUND))) {
>+				nr = HPAGE_PMD_NR;

This one trigger BUILD_BUG() if !PGTABLE_HAS_HUGE_LEAVES.

>+				src_pfns[i] &= ~MIGRATE_PFN_COMPOUND;
>+				src_pfns[i] &= ~MIGRATE_PFN_MIGRATE;
>+				goto next;
>+			}
>+
>+			migrate_vma_insert_page(migrate, addr, &dst_pfns[i],
> 						&src_pfns[i]);
>-			continue;
>+			goto next;

-- 
Wei Yang
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