+ mm-migrate-calculate-large-folio-page-index-using-pfn.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm/migrate: calculate large folio page index using PFN
has been added to the -mm mm-unstable branch.  Its filename is
     mm-migrate-calculate-large-folio-page-index-using-pfn.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate-calculate-large-folio-page-index-using-pfn.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Lorenzo Stoakes (ARM)" <ljs@kernel.org>
Subject: mm/migrate: calculate large folio page index using PFN
Date: Thu, 13 Aug 2026 18:32:30 +0100

Rather than having to figure out the page index to use using
linear_page_index(), calculate it using PFN.

This is a more natural fit as the linear page index is immaterial to
determining the folio page index.

Derive the page index from the offset between migration entry PFN and
folio PFN - pvmw.pfn (set via DEFINE_FOLIO_VMA_WALK() which uses
folio_pfn() to obtain it).

Additionally remove a not so useful comment and clean the code layout up.

No functional change intended.

Link: https://lore.kernel.org/20260813-b4-scalable-cow-virt-pgoff-v5-13-c21581c0c3c8@kernel.org
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Deucher <alexander.deucher@amd.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <baoquan.he@linux.dev>
Cc: Barry Song <baohua@kernel.org>
Cc: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Chris Li <chrisl@kernel.org>
Cc: Christan König <christian.koenig@amd.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Liviu Dudau <liviu.dudau@arm.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Marc Rutland <mark.rutland@arm.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>
Cc: Matthew Auld <matthew.auld@intel.com>
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Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Thomas Zimemrmann <tzimmermann@suse.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: xu xin <xu.xin16@zte.com.cn>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate.c |   19 +++++++++----------
 1 file changed, 9 insertions(+), 10 deletions(-)

--- a/mm/migrate.c~mm-migrate-calculate-large-folio-page-index-using-pfn
+++ a/mm/migrate.c
@@ -356,16 +356,11 @@ static bool remove_migration_pte(struct
 
 	while (page_vma_mapped_walk(&pvmw)) {
 		rmap_t rmap_flags = RMAP_NONE;
-		pte_t old_pte;
-		pte_t pte;
+		unsigned long idx = 0;
 		softleaf_t entry;
 		struct page *new;
-		unsigned long idx = 0;
-
-		/* pgoff is invalid for ksm pages, but they are never large */
-		if (folio_test_large(folio) && !folio_test_hugetlb(folio))
-			idx = linear_page_index(vma, pvmw.address) - pvmw.pgoff;
-		new = folio_page(folio, idx);
+		pte_t old_pte;
+		pte_t pte;
 
 #ifdef CONFIG_ARCH_HAS_PMD_SOFTLEAVES
 		/* PMD-mapped THP migration entry */
@@ -381,14 +376,18 @@ static bool remove_migration_pte(struct
 						pvmw.pte);
 		else
 			old_pte = ptep_get(pvmw.pte);
+
+		entry = softleaf_from_pte(old_pte);
+		if (folio_test_large(folio) && !folio_test_hugetlb(folio))
+			idx = softleaf_to_pfn(entry) - pvmw.pfn;
+
 		if (rmap_walk_arg->map_unused_to_zeropage &&
 		    try_to_map_unused_to_zeropage(&pvmw, folio, old_pte, idx))
 			continue;
 
 		folio_get(folio);
+		new = folio_page(folio, idx);
 		pte = mk_pte(new, READ_ONCE(vma->vm_page_prot));
-
-		entry = softleaf_from_pte(old_pte);
 		if (!softleaf_is_migration_young(entry))
 			pte = pte_mkold(pte);
 		if (folio_test_dirty(folio) && softleaf_is_migration_dirty(entry))
_

Patches currently in -mm which might be from ljs@kernel.org are

mm-vma-introduce-vma-anon-page-offset-field-and-add-helpers.patch
mm-provide-vma_is_cow_mapping-and-remove-is_cow_mapping.patch
mm-introduce-linear_anon_page_index.patch
mm-abstract-vma_address-and-introduce-vma_anon_address.patch
mm-update-print_bad_page_map-to-show-anon-index-if-appropriate.patch
mm-introduce-and-use-vma_filebacked_address.patch
mm-vma-fix-self-merge-check-in-copy_vma.patch
tools-testing-vma-add-tests-for-copy_vma-self-merge.patch
mm-propagate-vma-anonymous-page-offset-on-map-remap-split-merge.patch
mm-rmap-track-whether-the-page-vma-mapped-pgoff-is-anonymous.patch
mm-clean-up-vma_address_end.patch
mm-huge_memory-update-remove_migration_pmd-to-accept-a-folio.patch
mm-migrate-calculate-large-folio-page-index-using-pfn.patch
mm-rmap-use-anon-pgoff-to-track-map_private-file-backed-anon-folios.patch
tools-testing-vma-expand-vma-merge-tests-to-assert-anon-pgoff.patch
tools-testing-selftests-mm-test-anonymous-page-offset-merge-behaviour.patch
mm-add-some-missing-includes-to-mm-local-headers.patch
maintainers-add-drivers-char-memc-to-mm-misc-memory-mapping-sections.patch