+ proc-task_mmu-remove-special-casing-of-smap_gather_stats-start-parameter.patch added to mm-new branch

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

The patch titled
     Subject: proc/task_mmu: remove special-casing of smap_gather_stats() start parameter
has been added to the -mm mm-new branch.  Its filename is
     proc-task_mmu-remove-special-casing-of-smap_gather_stats-start-parameter.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/proc-task_mmu-remove-special-casing-of-smap_gather_stats-start-parameter.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: Suren Baghdasaryan <surenb@google.com>
Subject: proc/task_mmu: remove special-casing of smap_gather_stats() start parameter
Date: Fri, 11 Sep 2026 12:41:42 -0700

smap_gather_stats() interprets its start parameter to mean vma->vm_start
when it's set to 0.  Eliminate this special interpretation and provide two
separate functions for a partial and complete VMA walk.

Since smap_gather_stats() operates within a single VMA, we can replace
walk_page_vma()/walk_page_range() calls with walk_page_range_vma() which
is simpler and also can be called while holding per-VMA lock.

No functional change intended.

Link: https://lore.kernel.org/20260911194145.1781926-5-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Suggested by: Lorenzo Stoakes <ljs@kernel.org>
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: David Hildenbrand (Arm) <david@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <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 |   52 ++++++++++++++++++++++++++++---------------
 1 file changed, 35 insertions(+), 17 deletions(-)

--- a/fs/proc/task_mmu.c~proc-task_mmu-remove-special-casing-of-smap_gather_stats-start-parameter
+++ a/fs/proc/task_mmu.c
@@ -1246,20 +1246,26 @@ get_smaps_shmem_walk_ops(struct proc_map
 	return &smaps_shmem_walk_vma_lock_ops;
 }
 
-/*
- * Gather mem stats from @vma with the indicated beginning
- * address @start, and keep them in @mss.
+/**
+ * smap_gather_stats_range() - Gather mem stats from a portion of the @vma.
+ * @priv: proc maps private state.
+ * @vma: The VMA to gather stats for.
+ * @mss: The accumulated stats.
+ * @start: The address from which to start.
  *
- * Use vm_start of @vma as the beginning address if @start is 0.
+ * This gathers stats for the portion of the VMA starting at the @start
+ * address.
  */
-static void smap_gather_stats(struct proc_maps_private *priv,
-			      struct vm_area_struct *vma,
-			      struct mem_size_stats *mss, unsigned long start)
+static void smap_gather_stats_range(struct proc_maps_private *priv,
+		struct vm_area_struct *vma,
+		struct mem_size_stats *mss,
+		unsigned long start)
 {
 	const struct mm_walk_ops *ops = get_smaps_walk_ops(priv);
+	const bool is_partial = start > vma->vm_start;
 
 	/* Invalid start */
-	if (start >= vma->vm_end)
+	if (start < vma->vm_start || start >= vma->vm_end)
 		return;
 
 	if (vma == get_gate_vma(priv->lock_ctx.mm))
@@ -1278,20 +1284,31 @@ static void smap_gather_stats(struct pro
 		const unsigned long shmem_swapped = shmem_swap_usage(vma);
 		const bool is_cow = vma_is_cow_mapping(vma);
 
-		if (start || (shmem_swapped && is_cow))
+		if (is_partial || (shmem_swapped && is_cow))
 			ops = get_smaps_shmem_walk_ops(priv);
 		else
 			mss->swap += shmem_swapped;
 	}
 
-	if (!start)
-		walk_page_vma(vma, ops, mss);
-	else
-		walk_page_range(vma->vm_mm, start, vma->vm_end, ops, mss);
+	walk_page_range_vma(vma, start, vma->vm_end, ops, mss);
 
 	reacquire_rcu(priv);
 }
 
+/**
+ * smap_gather_stats() - Gather mem stats from the entire @vma.
+ * @priv: proc maps private state.
+ * @vma: The VMA to gather stats for.
+ * @mss: The accumulated stats.
+ *
+ * This gathers stats for the whole of the VMA.
+ */
+static void smap_gather_stats(struct proc_maps_private *priv,
+		struct vm_area_struct *vma, struct mem_size_stats *mss)
+{
+	smap_gather_stats_range(priv, vma, mss, vma->vm_start);
+}
+
 #define SEQ_PUT_DEC(str, val) \
 		seq_put_decimal_ull_width(m, str, (val) >> 10, 8)
 
@@ -1342,7 +1359,7 @@ static int show_smap(struct seq_file *m,
 	struct vm_area_struct *vma = v;
 	struct mem_size_stats mss = {};
 
-	smap_gather_stats(priv, vma, &mss, 0);
+	smap_gather_stats(priv, vma, &mss);
 
 	show_map_vma(m, vma);
 
@@ -1395,7 +1412,7 @@ static int show_smaps_rollup(struct seq_
 
 	vma_start = vma->vm_start;
 	do {
-		smap_gather_stats(priv, vma, &mss, 0);
+		smap_gather_stats(priv, vma, &mss);
 		last_vma_end = vma->vm_end;
 
 		/*
@@ -1454,14 +1471,15 @@ static int show_smaps_rollup(struct seq_
 
 			/* Case 1 and 2 above */
 			if (vma->vm_start >= last_vma_end) {
-				smap_gather_stats(priv, vma, &mss, 0);
+				smap_gather_stats(priv, vma, &mss);
 				last_vma_end = vma->vm_end;
 				continue;
 			}
 
 			/* Case 4 above */
 			if (vma->vm_end > last_vma_end) {
-				smap_gather_stats(priv, vma, &mss, last_vma_end);
+				smap_gather_stats_range(priv, vma, &mss,
+							last_vma_end);
 				last_vma_end = vma->vm_end;
 			}
 		}
_

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

proc-task_mmu-remove-unnecessary-helpers.patch
proc-task_mmu-remove-unnecessary-inlines-in-function-definitions.patch
proc-task_mmu-clarify-shmem-mapping-walk-conditions-in-smap_gather_stats.patch
proc-task_mmu-remove-special-casing-of-smap_gather_stats-start-parameter.patch
proc-task_mmu-change-proc_get_vma-to-stop-returning-gate-vma-at-the-end.patch
proc-task_mmu-read-proc-pid-smaps_rollup-under-per-vma-lock.patch
selftests-proc-add-proc-pid-smaps_rollup-tearing-tests.patch