[patch] mm, mempolicy: migrate_to_node should only migrate to node

[patch] mm, mempolicy: migrate_to_node should only migrate to node

[David Rientjes]

migrate_to_node() is intended to migrate a page from one source node to a 
target node.

Today, migrate_to_node() could end up migrating to any node, not only the 
target node.  This is because the page migration allocator, 
new_node_page() does not pass __GFP_THISNODE to alloc_pages_exact_node().  
This causes the target node to be preferred but allows fallback to any 
other node in order of affinity.

Prevent this by allocating with __GFP_THISNODE.  If memory is not 
available, -ENOMEM will be returned as appropriate.

Signed-off-by: David Rientjes <rientjes@google.com>
---
 mm/mempolicy.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -945,7 +945,8 @@ static struct page *new_node_page(struct page *page, unsigned long node, int **x
 		return alloc_huge_page_node(page_hstate(compound_head(page)),
 					node);
 	else
-		return alloc_pages_exact_node(node, GFP_HIGHUSER_MOVABLE, 0);
+		return alloc_pages_exact_node(node, GFP_HIGHUSER_MOVABLE |
+						    __GFP_THISNODE, 0);
 }
 
 /*

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Re: [patch] mm, mempolicy: migrate_to_node should only migrate to node

[Naoya Horiguchi]

On Tue, Feb 24, 2015 at 03:18:06PM -0800, David Rientjes wrote:
> migrate_to_node() is intended to migrate a page from one source node to a 
> target node.
> 
> Today, migrate_to_node() could end up migrating to any node, not only the 
> target node.  This is because the page migration allocator, 
> new_node_page() does not pass __GFP_THISNODE to alloc_pages_exact_node().  
> This causes the target node to be preferred but allows fallback to any 
> other node in order of affinity.
> 
> Prevent this by allocating with __GFP_THISNODE.  If memory is not 
> available, -ENOMEM will be returned as appropriate.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

Make sense to me.

Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
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