From: zhong jiang <redacted>

Accoding to HUgh's suggestion, alloc_stable_node() with GFP_KERNEL
will cause the hungtask, despite less possiblity.

At present, if alloc_stable_node allocate fails, two break_cow may
want to allocate a couple of pages, and the issue will come up when
free memory is under pressure.

we fix it by adding the __GFP_HIGH to GFP. because it grant access to
some of meory reserves. it will make progess to make it allocation
successful at the utmost.

--- a/mm/ksm.c
+++ b/mm/ksm.c

@@ -299,7 +299,7 @@ static inline void free_rmap_item(struct rmap_item *rmap_item)
 
 static inline struct stable_node *alloc_stable_node(void)
 {
-	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL);
+	return kmem_cache_alloc(stable_node_cache, GFP_KERNEL | __GFP_HIGH);
 }
 
 static inline void free_stable_node(struct stable_node *stable_node)