Re: [PATCH V3 0/2] mm/kvm/vfio/ppc64: Migrate compound pages out of CMA region

From: Aneesh Kumar K.V
Date: Thu Oct 04 2018 - 04:34:43 EST



Hi Andrew,

"Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> writes:

> ppc64 use CMA area for the allocation of guest page table (hash page table). We won't
> be able to start guest if we fail to allocate hash page table. We have observed
> hash table allocation failure because we failed to migrate pages out of CMA region
> because they were pinned. This happen when we are using VFIO. VFIO on ppc64 pins
> the entire guest RAM. If the guest RAM pages get allocated out of CMA region, we
> won't be able to migrate those pages. The pages are also pinned for the lifetime of the
> guest.
>
> Currently we support migration of non-compound pages. With THP and with the addition of
> hugetlb migration we can end up allocating compound pages from CMA region. This
> patch series add support for migrating compound pages. The first path adds the helper
> get_user_pages_cma_migrate() which pin the page making sure we migrate them out of
> CMA region before incrementing the reference count.
>
> Aneesh Kumar K.V (2):
> mm: Add get_user_pages_cma_migrate
> powerpc/mm/iommu: Allow migration of cma allocated pages during
> mm_iommu_get
>
> arch/powerpc/mm/mmu_context_iommu.c | 120 ++++++++-----------------
> include/linux/hugetlb.h | 2 +
> include/linux/migrate.h | 3 +
> mm/hugetlb.c | 4 +-
> mm/migrate.c | 132 ++++++++++++++++++++++++++++
> 5 files changed, 174 insertions(+), 87 deletions(-)

Any feedback on this.

-aneesh