Re: [PATCH] mm,ksm: add __GFP_HIGH to the allocation in alloc_stable_node()

On 2016/9/21 5:06, Andrew Morton wrote:

On Tue, 20 Sep 2016 14:54:44 +0800 zhongjiang [off-list ref] wrote:

quoted

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)

It is very hard for a reader to understand why this __GFP_HIGH is being
used here, so we should have a code comment explaining the reasoning,
please.

  ok,  I will add  some code comment later.

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