[PATCH 08/14] mm/ksm: document the two remove_rmap_item_from_tree() calls

[Longlong Xia]

From: Longlong Xia <xialonglong@xxxxxxxxxx>

Explain why cmp_and_merge_page() needs both tree-removal calls:
non-KSM pages are detached before the early returns, while KSM pages
are handled after stable_tree_search().

Assisted-by: Zcode:GLM-5.3
Signed-off-by: Longlong Xia <xialonglong@xxxxxxxxxx>

---
 mm/ksm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/mm/ksm.c b/mm/ksm.c
index 7fc9dac5d67c..1733b23cfaa2 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2313,6 +2313,10 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 		if (!is_page_sharing_candidate(stable_node))
 			max_page_sharing_bypass = true;
 	} else {
+		/*
+		 * Detach before the checksum and zero-page checks, which can
+		 * return without reaching the removal below.
+		 */
 		remove_rmap_item_from_tree(rmap_item);
 
 		/*
@@ -2338,6 +2342,10 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
 		return;
 	}
 
+	/*
+	 * A KSM page can still have an old tree association here; non-KSM
+	 * pages were already detached before the checks above.
+	 */
 	remove_rmap_item_from_tree(rmap_item);
 
 	if (kfolio) {
-- 
2.43.0