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Mon, 12 Aug 2024 16:12:52 -0700 (PDT) Received: from ziepe.ca ([128.77.69.90]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7a4c7d79076sm286600585a.60.2024.08.12.16.12.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Aug 2024 16:12:51 -0700 (PDT) Received: from jgg by wakko with local (Exim 4.95) (envelope-from ) id 1sdeDZ-003VqS-T1; Mon, 12 Aug 2024 20:12:49 -0300 Date: Mon, 12 Aug 2024 20:12:49 -0300 From: Jason Gunthorpe To: Christoph Hellwig Cc: Martin Oliveira , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Artemy Kovalyov , Greg Kroah-Hartman , Leon Romanovsky , Logan Gunthorpe , Michael Guralnik , Mike Marciniszyn , Shiraz Saleem , Tejun Heo , John Hubbard , Dan Williams , David Sloan Subject: Re: [PATCH v5 3/4] mm/gup: allow FOLL_LONGTERM & FOLL_PCI_P2PDMA Message-ID: <20240812231249.GG1985367@ziepe.ca> References: <20240808183340.483468-1-martin.oliveira@eideticom.com> <20240808183340.483468-4-martin.oliveira@eideticom.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 0AEE540021 X-Rspamd-Server: rspam01 X-Stat-Signature: ru1xdm3qdhzh7z5dej5g6itj9jnuaiku X-HE-Tag: 1723504372-868634 X-HE-Meta: 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 XMDZ2U6W dki05B3lFjGtBPn6npdzlB2AwkgvcBqDudAxeAf9pdCLmKzLS1rew5giSWg3Y4erZcNANNMp6JikJiB88crju1Jxjxf4UfqYTnK5DkQFxsIcAX2Qx3LH4V46ZE8aNK3LGoiu3U1iayyXSZZWQjbfwNmViE9JAQIOMh1Jd2vLJiiOqSIGbHkA8NxgjsvpncXFz3Z/luH7Wr2Zv/JSpnJYJPkS4/upRmLyXCC7zK5fDUp07QwxGyIRTWNADqianzkl4JPYclc3aMtgtPgh/CbucUqoXpoTKZve/zoAu0SsJpeLK3SFNMVkX4I9QUAVSRk9CaL7e6yGiaj9nP9E= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Aug 11, 2024 at 11:39:22PM -0700, Christoph Hellwig wrote: > On Thu, Aug 08, 2024 at 12:33:39PM -0600, Martin Oliveira wrote: > > This check existed originally due to concerns that P2PDMA needed to copy > > fsdax until pgmap refcounts were fixed (see [1]). > > > > The P2PDMA infrastructure will only call unmap_mapping_range() when the > > underlying device is unbound, and immediately after unmapping it waits > > for the reference of all ZONE_DEVICE pages to be released before > > continuing. This does not allow for a page to be reused and no user > > access fault is therefore possible. It does not have the same problem as > > fsdax. > > > > The one minor concern with FOLL_LONGTERM pins is they will block device > > unbind until userspace releases them all. > > This is unfortunately not really minor unless we have a well documented > way to force this :( It is not that different from blocking driver unbind while FDs are open which a lot of places do in various ways? Jason