From: Jason Gunthorpe Date: Mon, 20 Jul 2020 19:59:43 +0000 Subject: Re: [PATCH v2 2/5] mm/migrate: add a direction parameter to migrate_vma Message-Id: <20200720195943.GH2021234@nvidia.com> List-Id: References: <20200713172149.2310-1-rcampbell@nvidia.com> <20200713172149.2310-3-rcampbell@nvidia.com> <20200720183643.GA3028737@nvidia.com> <2e775a5d-9d62-de52-6799-3bbb09c88c5a@nvidia.com> In-Reply-To: <2e775a5d-9d62-de52-6799-3bbb09c88c5a@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Ralph Campbell Cc: linux-rdma@vger.kernel.org, linux-mm@kvack.org, nouveau@lists.freedesktop.org, kvm-ppc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Jerome Glisse , John Hubbard , Christoph Hellwig , Andrew Morton , Shuah Khan , Ben Skeggs , Bharata B Rao On Mon, Jul 20, 2020 at 12:54:53PM -0700, Ralph Campbell wrote: > > > diff --git a/include/linux/migrate.h b/include/linux/migrate.h > > > index 3e546cbf03dd..620f2235d7d4 100644 > > > +++ b/include/linux/migrate.h > > > @@ -180,6 +180,11 @@ static inline unsigned long migrate_pfn(unsigned long pfn) > > > return (pfn << MIGRATE_PFN_SHIFT) | MIGRATE_PFN_VALID; > > > } > > > +enum migrate_vma_direction { > > > + MIGRATE_VMA_FROM_SYSTEM, > > > + MIGRATE_VMA_FROM_DEVICE_PRIVATE, > > > +}; > > > > I would have guessed this is more natural as _FROM_DEVICE_ and > > TO_DEVICE_ ? > > The caller controls where the destination memory is allocated so it isn't > necessarily device private memory, it could be from system to system. > The use case for system to system memory migration is for hardware > like ARM SMMU or PCIe ATS where a single set of page tables is shared by > the device and a CPU process over a coherent system memory bus. > Also many integrated GPUs in SOCs fall into this category too. Maybe just TO/FROM_DEIVCE then? Even though the memory is not DEVICE_PRIVATE it is still device owned pages right? > So to me, it makes more sense to specify the direction based on the > source location. It feels strange because the driver doesn't always know or control the source? Jason