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SubjectRe: [shm][hugetlb] Fix get_policy for stacked shared memory files
On 6/12/07, Eric W. Biederman <ebiederm@xmission.com> wrote:
> Adam Litke <agl@us.ibm.com> writes:
>
> > 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?
>
> I'm confused.
>
> I agree that the behavior you describe is correct.
> However I only see two code paths were get_policy is called and
> both of them take a NULL result and change it to task->mempolicy:

The coffee hasn't quite absorbed yet, but don't those two code paths
take a NULL result from get_policy() and turn it into default_policy,
not task->mempolicy?

> From mm/mempolicy.c
>
> > long do_get_mempolicy(int *policy, nodemask_t *nmask,
> > unsigned long addr, unsigned long flags)
> > {
> > int err;
> > struct mm_struct *mm = current->mm;
> > struct vm_area_struct *vma = NULL;
> > struct mempolicy *pol = current->mempolicy;
> >
> > cpuset_update_task_memory_state();
> > if (flags & ~(unsigned long)(MPOL_F_NODE|MPOL_F_ADDR))
> > return -EINVAL;
> > if (flags & MPOL_F_ADDR) {
> > down_read(&mm->mmap_sem);
> > vma = find_vma_intersection(mm, addr, addr+1);
> > if (!vma) {
> > up_read(&mm->mmap_sem);
> > return -EFAULT;
> > }
> > if (vma->vm_ops && vma->vm_ops->get_policy)
> > pol = vma->vm_ops->get_policy(vma, addr);
> > else
> > pol = vma->vm_policy;
> > } else if (addr)
> > return -EINVAL;
> >
> > if (!pol)
> > pol = &default_policy;
>
>
>
> > /* Return effective policy for a VMA */
> > static struct mempolicy * get_vma_policy(struct task_struct *task,
> > struct vm_area_struct *vma, unsigned long addr)
> > {
> > struct mempolicy *pol = task->mempolicy;
> >
> > if (vma) {
> > if (vma->vm_ops && vma->vm_ops->get_policy)
> > pol = vma->vm_ops->get_policy(vma, addr);
> > else if (vma->vm_policy &&
> > vma->vm_policy->policy != MPOL_DEFAULT)
> > pol = vma->vm_policy;
> > }
> > if (!pol)
> > pol = &default_policy;
> > return pol;
> > }
>
>
> Does this perhaps need to be:
> > 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)
>
> + pol = NULL;
> >
> > if (sfd->vm_ops->get_policy)
> > pol = sfd->vm_ops->get_policy(vma, addr);
> > - else
> > + else if (vma->vm_policy && vma->vm_policy->policy != MPOL_DEFAULT)
> > pol = vma->vm_policy;
> > return pol;
> > }
> > #endif

afaict this would provide no way for pol to be set to task->mempolicy
for hugetlb per my comment above.

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