linux-kernel - [PATCH 3/3] ksm: replace function unmerge_ksm_pages with break

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Message-ID: <20251028131945.26445-4-pedrodemargomes@gmail.com>
Date: Tue, 28 Oct 2025 10:19:45 -0300
From: Pedro Demarchi Gomes <pedrodemargomes@...il.com>
To: David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: Xu Xin <xu.xin16@....com.cn>,
	Chengming Zhou <chengming.zhou@...ux.dev>,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Pedro Demarchi Gomes <pedrodemargomes@...il.com>
Subject: [PATCH 3/3] ksm: replace function unmerge_ksm_pages with break_ksm

Function unmerge_ksm_pages() is unnecessary since now break_ksm() walks
an address range. So replace it with break_ksm().

Suggested-by: David Hildenbrand <david@...hat.com>
Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@...il.com>
---
 mm/ksm.c | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 1d1ef0554c7c..18c9e3bda285 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -669,6 +669,18 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = {
 };
 
 /*
+ * Though it's very tempting to unmerge rmap_items from stable tree rather
+ * than check every pte of a given vma, the locking doesn't quite work for
+ * that - an rmap_item is assigned to the stable tree after inserting ksm
+ * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
+ * rmap_items from parent to child at fork time (so as not to waste time
+ * if exit comes before the next scan reaches it).
+ *
+ * Similarly, although we'd like to remove rmap_items (so updating counts
+ * and freeing memory) when unmerging an area, it's easier to leave that
+ * to the next pass of ksmd - consider, for example, how ksmd might be
+ * in cmp_and_merge_page on one of the rmap_items we would be removing.
+ *
  * We use break_ksm to break COW on a ksm page by triggering unsharing,
  * such that the ksm page will get replaced by an exclusive anonymous page.
  *
@@ -1077,25 +1089,6 @@ static void remove_trailing_rmap_items(struct ksm_rmap_item **rmap_list)
 	}
 }
 
-/*
- * Though it's very tempting to unmerge rmap_items from stable tree rather
- * than check every pte of a given vma, the locking doesn't quite work for
- * that - an rmap_item is assigned to the stable tree after inserting ksm
- * page and upping mmap_lock.  Nor does it fit with the way we skip dup'ing
- * rmap_items from parent to child at fork time (so as not to waste time
- * if exit comes before the next scan reaches it).
- *
- * Similarly, although we'd like to remove rmap_items (so updating counts
- * and freeing memory) when unmerging an area, it's easier to leave that
- * to the next pass of ksmd - consider, for example, how ksmd might be
- * in cmp_and_merge_page on one of the rmap_items we would be removing.
- */
-static int unmerge_ksm_pages(struct vm_area_struct *vma,
-			     unsigned long start, unsigned long end, bool lock_vma)
-{
-	return break_ksm(vma, start, end, lock_vma);
-}
-
 static inline
 struct ksm_stable_node *folio_stable_node(const struct folio *folio)
 {
@@ -1233,7 +1226,7 @@ static int unmerge_and_remove_all_rmap_items(void)
 		for_each_vma(vmi, vma) {
 			if (!(vma->vm_flags & VM_MERGEABLE) || !vma->anon_vma)
 				continue;
-			err = unmerge_ksm_pages(vma,
+			err = break_ksm(vma,
 						vma->vm_start, vma->vm_end, false);
 			if (err)
 				goto error;
@@ -2861,7 +2854,7 @@ static int __ksm_del_vma(struct vm_area_struct *vma)
 		return 0;
 
 	if (vma->anon_vma) {
-		err = unmerge_ksm_pages(vma, vma->vm_start, vma->vm_end, true);
+		err = break_ksm(vma, vma->vm_start, vma->vm_end, true);
 		if (err)
 			return err;
 	}
@@ -3013,7 +3006,7 @@ int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
 			return 0;		/* just ignore the advice */
 
 		if (vma->anon_vma) {
-			err = unmerge_ksm_pages(vma, start, end, true);
+			err = break_ksm(vma, start, end, true);
 			if (err)
 				return err;
 		}
@@ -3395,7 +3388,7 @@ static int ksm_memory_callback(struct notifier_block *self,
 		 * Prevent ksm_do_scan(), unmerge_and_remove_all_rmap_items()
 		 * and remove_all_stable_nodes() while memory is going offline:
 		 * it is unsafe for them to touch the stable tree at this time.
-		 * But unmerge_ksm_pages(), rmap lookups and other entry points
+		 * But break_ksm(), rmap lookups and other entry points
 		 * which do not need the ksm_thread_mutex are all safe.
 		 */
 		mutex_lock(&ksm_thread_mutex);
-- 
2.43.0