[merged mm-stable] proc-task_mmu-clarify-shmem-mapping-walk-conditions-in-smap_gather_stats.patch removed from -mm tree

[merged mm-stable] proc-task_mmu-clarify-shmem-mapping-walk-conditions-in-smap_gather_stats.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats()
has been removed from the -mm tree.  Its filename was
     proc-task_mmu-clarify-shmem-mapping-walk-conditions-in-smap_gather_stats.patch

This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Suren Baghdasaryan <surenb@google.com>
Subject: proc/task_mmu: clarify shmem mapping walk conditions in smap_gather_stats()
Date: Fri, 18 Sep 2026 08:33:14 -0700

smap_gather_stats() optimizes stats gathering by skipping the walk for
shmem mappings in certain conditions.  Update the comment to clarify these
conditions and use vma_is_cow_mapping() for CoW identification instead of
open-coding it.

No functional change intended.

Link: https://lore.kernel.org/20260918153318.758387-4-surenb@google.com
Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett (Oracle) <liam@infradead.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
---

 fs/proc/task_mmu.c |   23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

--- a/fs/proc/task_mmu.c~proc-task_mmu-clarify-shmem-mapping-walk-conditions-in-smap_gather_stats
+++ a/fs/proc/task_mmu.c
@@ -1274,23 +1274,18 @@ static void smap_gather_stats(struct pro
 
 	if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
 		/*
-		 * For shared or readonly shmem mappings we know that all
-		 * swapped out pages belong to the shmem object, and we can
-		 * obtain the swap value much more efficiently. For private
-		 * writable mappings, we might have COW pages that are
-		 * not affected by the parent swapped out pages of the shmem
-		 * object, so we have to distinguish them during the page walk.
-		 * Unless we know that the shmem object (or the part mapped by
-		 * our VMA) has no swapped out pages at all.
+		 * CoW mappings might map anon folios that do not belong to
+		 * shmem. Perform a less efficient page table walk in this
+		 * situation, unless we know that the shmem object (or the
+		 * part mapped by our VMA) has no swapped out pages at all.
 		 */
-		unsigned long shmem_swapped = shmem_swap_usage(vma);
+		const unsigned long shmem_swapped = shmem_swap_usage(vma);
+		const bool is_cow = vma_is_cow_mapping(vma);
 
-		if (!start && (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
-					!(vma->vm_flags & VM_WRITE))) {
-			mss->swap += shmem_swapped;
-		} else {
+		if (start || (shmem_swapped && is_cow))
 			ops = get_smaps_shmem_walk_ops(priv);
-		}
+		else
+			mss->swap += shmem_swapped;
 	}
 
 	if (!start)
_

Patches currently in -mm which might be from surenb@google.com are