+ mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping.patch added to mm-new branch

+ mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: mm/rmap: refactor some code around lazyfree folio unmapping
has been added to the -mm mm-new branch.  Its filename is
     mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping.patch

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

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Dev Jain <dev.jain@arm.com>
Subject: mm/rmap: refactor some code around lazyfree folio unmapping
Date: Mon, 13 Jul 2026 05:00:46 +0000

For lazyfree folio unmapping, after clearing the ptes we must abort the
operation if the folio got dirtied or it has unexpected references.

Refactor this logic into a function which will return whether we need to
abort or not.

If we abort, we restore the ptes and bail out of try_to_unmap_one. 
Otherwise adjust the rss stats of the mm and jump to a label.

Also rename that label from "discard" to "finish_unmap"; the former is
appropriate in the lazyfree context, but the code following the label is
executed for other successful unmap code paths too, so 'discard' does not
sound correct for them.

No functional change intended.

Link: https://lore.kernel.org/20260713050050.1017741-4-dev.jain@arm.com
Signed-off-by: Dev Jain <dev.jain@arm.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Harry Yoo <harry@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Rik van Riel <riel@surriel.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/rmap.c |   87 ++++++++++++++++++++++++++++------------------------
 1 file changed, 48 insertions(+), 39 deletions(-)

--- a/mm/rmap.c~mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping
+++ a/mm/rmap.c
@@ -2068,6 +2068,50 @@ range_end:
 	return ret;
 }
 
+static bool ttu_anon_lazyfree_folio(struct vm_area_struct *vma,
+		struct folio *folio, unsigned long nr_pages)
+{
+	int ref_count, map_count;
+
+	/*
+	 * Synchronize with gup_pte_range():
+	 * - clear PTE; barrier; read refcount
+	 * - inc refcount; barrier; read PTE
+	 */
+	smp_mb();
+
+	ref_count = folio_ref_count(folio);
+	map_count = folio_mapcount(folio);
+
+	/*
+	 * Order reads for page refcount and dirty flag
+	 * (see comments in __remove_mapping()).
+	 */
+	smp_rmb();
+
+	if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) {
+		/*
+		 * redirtied either using the page table or a previously
+		 * obtained GUP reference.
+		 */
+		folio_set_swapbacked(folio);
+		return false;
+	}
+
+	/*
+	 * Additional references could be due to GUP or speculative lookups.
+	 * GUP users must mark the folio dirty if there was a modification.
+	 * This folio cannot be reclaimed right now either way, so act just
+	 * like nothing happened. We'll come back here later and detect if the
+	 * folio was dirtied when the additional reference is gone.
+	 */
+	if (ref_count != 1 + map_count)
+		return false;
+
+	add_mm_counter(vma->vm_mm, MM_ANONPAGES, -nr_pages);
+	return true;
+}
+
 /*
  * @arg: enum ttu_flags will be passed to this argument
  */
@@ -2261,47 +2305,12 @@ static bool try_to_unmap_one(struct foli
 
 			/* MADV_FREE page check */
 			if (!folio_test_swapbacked(folio)) {
-				int ref_count, map_count;
-
-				/*
-				 * Synchronize with gup_pte_range():
-				 * - clear PTE; barrier; read refcount
-				 * - inc refcount; barrier; read PTE
-				 */
-				smp_mb();
-
-				ref_count = folio_ref_count(folio);
-				map_count = folio_mapcount(folio);
-
-				/*
-				 * Order reads for page refcount and dirty flag
-				 * (see comments in __remove_mapping()).
-				 */
-				smp_rmb();
-
-				if (folio_test_dirty(folio) && !(vma->vm_flags & VM_DROPPABLE)) {
-					/*
-					 * redirtied either using the page table or a previously
-					 * obtained GUP reference.
-					 */
-					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
-					folio_set_swapbacked(folio);
-					goto walk_abort;
-				} else if (ref_count != 1 + map_count) {
-					/*
-					 * Additional reference. Could be a GUP reference or any
-					 * speculative reference. GUP users must mark the folio
-					 * dirty if there was a modification. This folio cannot be
-					 * reclaimed right now either way, so act just like nothing
-					 * happened.
-					 * We'll come back here later and detect if the folio was
-					 * dirtied when the additional reference is gone.
-					 */
+				if (!ttu_anon_lazyfree_folio(vma, folio,
+							     nr_pages)) {
 					set_ptes(mm, address, pvmw.pte, pteval, nr_pages);
 					goto walk_abort;
 				}
-				add_mm_counter(mm, MM_ANONPAGES, -nr_pages);
-				goto discard;
+				goto finish_unmap;
 			}
 
 			if (folio_dup_swap(folio, subpage) < 0) {
@@ -2359,7 +2368,7 @@ static bool try_to_unmap_one(struct foli
 			 */
 			add_mm_counter(mm, mm_counter_file(folio), -nr_pages);
 		}
-discard:
+finish_unmap:
 		folio_remove_rmap_ptes(folio, subpage, nr_pages, vma);
 		if (vma->vm_flags & VM_LOCKED)
 			mlock_drain_local();
_

Patches currently in -mm which might be from dev.jain@arm.com are

mm-swap-rename-subpage-page-in-folio_dup_swap-folio_put_swap.patch
mm-mprotect-drop-sub-from-batching-context.patch
arm64-make-huge_ptep_get-handled-unaligned-addresses.patch
mm-rmap-use-huge_ptep_get-in-try_to_unmap_one.patch
mm-rmap-use-huge_ptep_get-in-try_to_migrate_one.patch
mm-migrate-use-huge_ptep_get-in-remove_migration_pte.patch
mm-page_vma_mapped-use-huge_ptep_get-for-hugetlb.patch
mm-mprotect-use-huge_ptep_get-for-hugetlb.patch
mm-rmap-convert-page-folio-for-hwpoison-checks.patch
mm-rmap-add-try_to_unmap_hugetlb_one.patch
mm-rmap-refactor-some-code-around-lazyfree-folio-unmapping.patch
mm-rmap-refactor-anon-folio-unmap-in-try_to_unmap_one.patch
mm-rmap-add-anon-folio-unmap-dispatcher.patch