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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id h17si6746361pgd.538.2019.02.06.12.41.33 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Wed, 06 Feb 2019 12:41:33 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=lGhu39iF; spf=pass (google.com: best guess record for domain of willy@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=willy@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=sWEKy5aicFMji7dfB83+mOjLcp3oFlOpybyajD/WoZQ=; b=lGhu39iFHGWpvbRYczilWLR4r 7fQM8YFJAZN8allzduj9Eody3bio+zBsadPFUnEagmSHYZVKNGx8DeHmVlJf5g04b9INUcxffjwRw chp0xai/x6avJiMiMNSWnltw+JWwe2rOvPKh6EG7f8BYYhWgNWWRztUWVLRZIuAIqb0M28gvV87QG kqinj6dE6kMmbuH1toWRNc026lLLmmUsYpu0pK2vhNbFdZ+MRRXMoDwOkgK0xm9YtBVTkG1Eb9WQz m0yL5r/pbWigkgHqlRfTSgy6arFOxnWWo/QmTSUMLcX5qBP8oYd3Y3KFQtpQuPzl+bMEBuwHlRMtY G2IgR77Iw==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1grU0e-0006kC-HG; Wed, 06 Feb 2019 20:41:28 +0000 Date: Wed, 6 Feb 2019 12:41:28 -0800 From: Matthew Wilcox To: Doug Ledford Cc: Christopher Lameter , Jason Gunthorpe , Jan Kara , Ira Weiny , lsf-pc@lists.linux-foundation.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, John Hubbard , Jerome Glisse , Dan Williams , Dave Chinner , Michal Hocko Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190206204128.GR21860@bombadil.infradead.org> References: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> <20190206095000.GA12006@quack2.suse.cz> <20190206173114.GB12227@ziepe.ca> <20190206175233.GN21860@bombadil.infradead.org> <47820c4d696aee41225854071ec73373a273fd4a.camel@redhat.com> <01000168c43d594c-7979fcf8-b9c1-4bda-b29a-500efe001d66-000000@email.amazonses.com> <20190206194055.GP21860@bombadil.infradead.org> <20190206202021.GQ21860@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) 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: On Wed, Feb 06, 2019 at 03:28:35PM -0500, Doug Ledford wrote: > On Wed, 2019-02-06 at 12:20 -0800, Matthew Wilcox wrote: > > On Wed, Feb 06, 2019 at 03:16:02PM -0500, Doug Ledford wrote: > > > On Wed, 2019-02-06 at 11:40 -0800, Matthew Wilcox wrote: > > > > On Wed, Feb 06, 2019 at 07:16:21PM +0000, Christopher Lameter wrote: > > > > > though? If we only allow this use case then we may not have to worry about > > > > > long term GUP because DAX mapped files will stay in the physical location > > > > > regardless. > > > > > > > > ... except for truncate. And now that I think about it, there was a > > > > desire to support hot-unplug which also needed revoke. > > > > > > We already support hot unplug of RDMA devices. But it is extreme. How > > > does hot unplug deal with a program running from the device (something > > > that would have returned ETXTBSY)? > > > > Not hot-unplugging the RDMA device but hot-unplugging an NV-DIMM. > > > > It's straightforward to migrate text pages from one DIMM to another; > > you remove the PTEs from the CPU's page tables, copy the data over and > > pagefaults put the new PTEs in place. We don't have a way to do similar > > things to an RDMA device, do we? > > We don't have a means of migration except in the narrowly scoped sense > of queue pair migration as defined by the IBTA and implemented on some > dual port IB cards. This narrowly scoped migration even still involves > notification of the app. > > Since there's no guarantee that any other port can connect to the same > machine as any port that's going away, it would always be a > disconnect/reconnect sequence in the app to support this, not an under > the covers migration. I don't understand you. We're not talking about migrating from one IB card to another, we're talking about changing the addresses that an STag refers to.