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SubjectRe: [shm][hugetlb] Fix get_policy for stacked shared memory files
On Mon, 11 Jun 2007 16:34:54 -0500 Adam Litke <agl@us.ibm.com> wrote:

> 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?
>

Can we just double-check the refcounting please?

> 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);

afacit this takes a ref on the underlying policy

> - else
> + else if (vma->vm_policy)
> pol = vma->vm_policy;
> + else
> + pol = current->mempolicy;

but these two do not.

> return pol;
> }
> #endif

Is is all correct?
-
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