The quilt patch titled
Subject: mm/ksm: remove page_mapcount() usage in stable_tree_search()
has been removed from the -mm tree. Its filename was
mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.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: David Hildenbrand <david@xxxxxxxxxx>
Subject: mm/ksm: remove page_mapcount() usage in stable_tree_search()
Date: Tue, 16 Apr 2024 19:25:33 +0200
We want to limit the use of page_mapcount() to the places where it is
absolutely necessary.
If our folio has a stable node, it is a (small) KSM folio -- see
folio_stable_node(). Let's use folio_mapcount() in stable_tree_search()
instead, which results in no functional change.
The mapcount > 1 check is a bit confusing, because that's usually a check
for page sharing. Looks like the reason is that we are guaranteed to not
exceed ksm_max_page_sharing for the tree KSM folio when merging with that.
Let's update the documentation to make that clearer.
Link: https://lkml.kernel.org/r/20240416172533.663418-1-david@xxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
Reviewed-by: Alex Shi <alexs@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/ksm.c | 13 ++++++++-----
1 file changed, 8 insertions(+), 5 deletions(-)
--- a/mm/ksm.c~mm-ksm-remove-page_mapcount-usage-in-stable_tree_search
+++ a/mm/ksm.c
@@ -1909,12 +1909,15 @@ again:
if (page_node) {
VM_BUG_ON(page_node->head != &migrate_nodes);
/*
- * Test if the migrated page should be merged
- * into a stable node dup. If the mapcount is
- * 1 we can migrate it with another KSM page
- * without adding it to the chain.
+ * If the mapcount of our migrated KSM folio is
+ * at most 1, we can merge it with another
+ * KSM folio where we know that we have space
+ * for one more mapping without exceeding the
+ * ksm_max_page_sharing limit: see
+ * chain_prune(). This way, we can avoid adding
+ * this stable node to the chain.
*/
- if (page_mapcount(page) > 1)
+ if (folio_mapcount(folio) > 1)
goto chain_append;
}
_
Patches currently in -mm which might be from david@xxxxxxxxxx are
