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[192.55.52.88]) by mx.google.com with ESMTPS id x23si3789173pln.100.2019.02.05.10.01.40 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 05 Feb 2019 10:01:40 -0800 (PST) Received-SPF: pass (google.com: domain of ira.weiny@intel.com designates 192.55.52.88 as permitted sender) client-ip=192.55.52.88; Authentication-Results: mx.google.com; spf=pass (google.com: domain of ira.weiny@intel.com designates 192.55.52.88 as permitted sender) smtp.mailfrom=ira.weiny@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 05 Feb 2019 10:01:40 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,336,1544515200"; d="scan'208";a="124180424" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by orsmga003.jf.intel.com with ESMTP; 05 Feb 2019 10:01:39 -0800 Date: Tue, 5 Feb 2019 10:01:20 -0800 From: Ira Weiny To: lsf-pc@lists.linux-foundation.org, linux-rdma@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: John Hubbard , Jan Kara , Jerome Glisse , Dan Williams , Matthew Wilcox , Dave Chinner , Doug Ledford , Michal Hocko , Jason Gunthorpe Subject: Re: [LSF/MM TOPIC] Discuss least bad options for resolving longterm-GUP usage by RDMA Message-ID: <20190205180120.GC21617@iweiny-DESK2.sc.intel.com> References: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190205175059.GB21617@iweiny-DESK2.sc.intel.com> User-Agent: Mutt/1.11.1 (2018-12-01) 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: I had an old invalid address for Jason Gunthorpe in my address book... Correcting his email in the thread. On Tue, Feb 05, 2019 at 09:50:59AM -0800, 'Ira Weiny' wrote: > > The problem: Once we have pages marked as GUP-pinned how should various > subsystems work with those markings. > > The current work for John Hubbards proposed solutions (part 1 and 2) is > progressing.[1] But the final part (3) of his solution is also going to take > some work. > > In Johns presentation he lists 3 alternatives for gup-pinned pages: > > 1) Hold off try_to_unmap > 2) Allow writeback while pinned (via bounce buffers) > [Note this will not work for DAX] > 3) Use a "revocable reservation" (or lease) on those pages > 4) Pin the blocks as busy in the FS allocator > > The problem with lease's on pages used by RDMA is that the references to > these pages is not local to the machine. Once the user has been given access > to the page they, through the use of a remote tokens, give a reference to that > page to remote nodes. This is the core essence of RDMA, and like it or not, > something which is increasingly used by major Linux users. > > Therefore we need to discuss the extent by which leases are appropriate and > what happens should a lease be revoked which a user does not respond to. > > As John Hubbard put it: > > "Other filesystem features that need to replace the page with a new one can > be inhibited for pages that are GUP-pinned. This will, however, alter and > limit some of those filesystem features. The only fix for that would be to > require GUP users monitor and respond to CPU page table updates. Subsystems > such as ODP and HMM do this, for example. This aspect of the problem is > still under discussion." > > -- John Hubbard[2] > > The following people have been involved in previous conversations and would be key to > the face to face discussion. > > John Hubbard > Jan Kara > Dave Chinner > Michal Hocko > Dan Williams > Matthew Wilcox > Jason Gunthorpe > > Thank you, > Ira Weiny > > [1] https://linuxplumbersconf.org/event/2/contributions/126/attachments/136/168/LPC_2018_gup_dma.pdf > [2] https://lkml.org/lkml/2019/2/4/7 >