[PATCH v2 3/3] ksm: replace function unmerge_ksm_pages with break_ksm

Pedro Demarchi Gomes
2025-10-31T17:48:56Z

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@redhat.com>
Signed-off-by: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
---
mm/ksm.c | 40 ++++++++++++++++------------------------
1 file changed, 16 insertions(+), 24 deletions(-)

diff --git a/mm/ksm.c b/mm/ksm.c
index 64d66699133d..7cd19a6ce45f 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.
*
@@ -1075,25 +1087,6 @@ 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)
{
@@ -1231,8 +1224,7 @@ 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,
- vma->vm_start, vma->vm_end, false);
+ err = break_ksm(vma, vma->vm_start, vma->vm_end, false);
if (err)
goto error;
}
@@ -2859,7 +2851,7 @@ 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;
}
@@ -3011,7 +3003,7 @@ 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;
}
@@ -3393,7 +3385,7 @@ 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