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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     akpm@linux-foundation.org, Michal Hocko <mhocko@kernel.org>,
        Alexey Kardashevskiy <aik@ozlabs.ru>, mpe@ellerman.id.au
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH V3 0/2] mm/kvm/vfio/ppc64: Migrate compound pages out of CMA region
In-Reply-To: <20180918115839.22154-1-aneesh.kumar@linux.ibm.com>
References: <20180918115839.22154-1-aneesh.kumar@linux.ibm.com>
Date:   Thu, 04 Oct 2018 14:04:29 +0530
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Hi Andrew,

"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> 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