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-rw-r--r--mm/ksm.c28
1 files changed, 28 insertions, 0 deletions
diff --git a/mm/ksm.c b/mm/ksm.c
index caa54a55a357..614b2cce9ad7 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -1469,8 +1469,22 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
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.
+ */
+ split = PageTransCompound(page)
+ && compound_head(page) == compound_head(tree_page);
put_page(tree_page);
if (kpage) {
/*
@@ -1495,6 +1509,20 @@ static void cmp_and_merge_page(struct page *page, struct rmap_item *rmap_item)
break_cow(tree_rmap_item);
break_cow(rmap_item);
}
+ } else if (split) {
+ /*
+ * We are here if we tried to merge two pages and
+ * failed because they both belonged to the same
+ * compound page. We will split the page now, but no
+ * merging will take place.
+ * We do not want to add the cost of a full lock; if
+ * the page is locked, it is better to skip it and
+ * perhaps try again later.
+ */
+ if (!trylock_page(page))
+ return;
+ split_huge_page(page);
+ unlock_page(page);
}
}
}