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.
Changes from V4:
* use __GFP_NOWARN when allocating pages to avoid page allocation failure warnings.
Changes from V3:
* Move the hugetlb check before transhuge check
* Use compound head page when isolating hugetlb page
Aneesh Kumar K.V (3):
mm: Add get_user_pages_cma_migrate
powerpc/mm/iommu: Allow migration of cma allocated pages during
mm_iommu_get
powerpc/mm/iommu: Allow large IOMMU page size only for hugetlb backing
arch/powerpc/mm/mmu_context_iommu.c | 140 ++++++++--------------------
include/linux/hugetlb.h | 2 +
include/linux/migrate.h | 3 +
mm/hugetlb.c | 4 +-
mm/migrate.c | 139 +++++++++++++++++++++++++++
5 files changed, 186 insertions(+), 102 deletions(-)
--
2.19.2
