From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alistair Popple Date: Wed, 31 Mar 2021 13:27:52 +0000 Subject: Re: [PATCH v7 5/8] mm: Device exclusive memory access Message-Id: <2124945.3NMGunUBXV@nvdebian> List-Id: References: <20210326000805.2518-1-apopple@nvidia.com> <2521635.masqiumSp9@nvdebian> <20210331131854.GI1463678@nvidia.com> In-Reply-To: <20210331131854.GI1463678@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jason Gunthorpe Cc: linux-mm@kvack.org, nouveau@lists.freedesktop.org, bskeggs@redhat.com, akpm@linux-foundation.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, dri-devel@lists.freedesktop.org, jhubbard@nvidia.com, rcampbell@nvidia.com, jglisse@redhat.com, hch@infradead.org, daniel@ffwll.ch, willy@infradead.org, Christoph Hellwig On Thursday, 1 April 2021 12:18:54 AM AEDT Jason Gunthorpe wrote: > On Wed, Mar 31, 2021 at 11:59:28PM +1100, Alistair Popple wrote: > > > I guess that makes sense as the split could go either way at the > > moment but I should add a check to make sure this isn't used with > > pinned pages anyway. > > Is it possible to have a pinned page under one of these things? If I > pin it before you migrate it then it remains pinned but hidden under > the swap entry? At the moment yes. But I had planned (and this reminded me) to add a check to prevent marking pinned pages for exclusive access. This check was in the original migration based implementation as I don't think it makes much sense to allow exclusive access to pinned pages given it indicates another device is possibly using it. > So the special logic is needed and the pinned page has to be copied > and written as a normal pte, not dropped as a migration entry Yep, if we end up allowing pinned pages to exist under these then that makes sense. Thanks for the clarification. - Alistair > Jason >