[shm][hugetlb] Fix get_policy for stacked shared memory files

[Adam Litke <agl@us.ibm.com>]

Here's another breakage as a result of shared memory stacked files :(

The NUMA policy for a VMA is determined by checking the following (in the order
given):

1) vma->vm_ops->get_policy() (if defined)
2) vma->vm_policy (if defined)
3) task->mempolicy (if defined)
4) Fall back to default_policy

By switching to stacked files for shared memory, get_policy() is now always set
to shm_get_policy which is a wrapper function.  This causes us to stop at step
1, which yields NULL for hugetlb instead of task->mempolicy which was the
previous (and correct) result.

This patch modifies the shm_get_policy() wrapper to maintain steps 1-3 for the
wrapped vm_ops.  Andi and Christoph, does this look right to you?

Signed-off-by: Adam Litke <agl@us.ibm.com>

diff --git a/ipc/shm.c b/ipc/shm.c
index 4fefbad..8d2672d 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -254,8 +254,10 @@ struct mempolicy *shm_get_policy(struct vm_area_struct *vma, unsigned long addr)
 
 	if (sfd->vm_ops->get_policy)
 		pol = sfd->vm_ops->get_policy(vma, addr);
-	else
+	else if (vma->vm_policy)
 		pol = vma->vm_policy;
+	else
+		pol = current->mempolicy;
 	return pol;
 }
 #endif

-- 
Adam Litke - (agl at us.ibm.com)
IBM Linux Technology Center