Re: [PATCH] mm: mempolicy: keep VMA walk if both MPOL_MF_STRICT and MPOL_MF_MOVE are specified

Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx> · Thu, 28 Sep 2023 10:35:17 -0700

On 9/28/23 9:38 AM, Andrew Morton wrote:
On Wed, 27 Sep 2023 14:39:21 -0700 Suren Baghdasaryan <surenb@xxxxxxxxxx> wrote:

The code should conceptually do:

   if (MPOL_MF_MOVE|MOVEALL)
       scan all vmas
       try to migrate the existing pages
       return success
   else if (MPOL_MF_MOVE* | MPOL_MF_STRICT)
       scan all vmas
       try to migrate the existing pages
       return -EIO if unmovable or migration failed
   else /* MPOL_MF_STRICT alone */
       break early if meets unmovable and don't call mbind_range() at all
   else /* none of those flags */
       check the ranges in test_walk, EFAULT without mbind_range() if discontig.
With this change I think my temporary fix at
https://lore.kernel.org/all/20230918211608.3580629-1-surenb@xxxxxxxxxx/
can be removed because we either scan all vmas (which means we locked
them all) or we break early and do not call mbind_range() at all (in
which case we don't need vmas to be locked).

Yes, we could just drop it. Keep the code not depend on the subtle 
behavior of queue_pages_range() by keeping it is ok to me either. I 
don't have strong preference.

Thanks, I dropped "mm: lock VMAs skipped by a failed queue_pages_range()"

Thanks, Andrew.