On 15.11.23 04:11, xu wrote:
diff --git a/mm/ksm.c b/mm/ksm.c
index 7efcc68ccc6e..c952fe5d9e43 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -2229,24 +2229,10 @@ static void cmp_and_merge_page(struct page *page, struct ksm_rmap_item *rmap_ite
tree_rmap_item =
unstable_tree_search_insert(rmap_item, page, &tree_page);
if (tree_rmap_item) {
- bool split;
-
kpage = try_to_merge_two_pages(rmap_item, page,
tree_rmap_item, tree_page);
- /*
- * If both pages we tried to merge belong to the same compound
- * page, then we actually ended up increasing the reference
- * count of the same compound page twice, and split_huge_page
- * failed.
- * Here we set a flag if that happened, and we use it later to
- * try split_huge_page again. Since we call put_page right
- * afterwards, the reference count will be correct and
- * split_huge_page should succeed.
- */
I'm curious, why can't we detect that ahead of time and keep only a
single reference? Why do we need the backup code? Anything I am missing?
I don't know the original reason, better ask Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>.
Maybe because doing detection that ahead of time will break several funtions' semantic,
such as try_to_merge_two_pages(), try_to_merge_with_ksm_page() and try_to_merge_one_page()
Adding the backup code don't change the old code and fixing the old problem, it's good.
It's absolutely counter-intuitive to check for something that cannot
possibly work after the effects. This better has a good reason to make
that code more complicated.
--
Cheers,
David / dhildenb
