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[156.34.55.100]) by smtp.gmail.com with ESMTPSA id q36sm1286394qtc.12.2019.06.07.05.17.29 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 07 Jun 2019 05:17:29 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1hZDoH-0006pJ-3U; Fri, 07 Jun 2019 09:17:29 -0300 Date: Fri, 7 Jun 2019 09:17:29 -0300 From: Jason Gunthorpe To: Jan Kara Cc: Ira Weiny , Dan Williams , Theodore Ts'o , Jeff Layton , Dave Chinner , Matthew Wilcox , linux-xfs@vger.kernel.org, Andrew Morton , John Hubbard , =?utf-8?B?SsOpcsO0bWU=?= Glisse , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-ext4@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal Message-ID: <20190607121729.GA14802@ziepe.ca> References: <20190606014544.8339-1-ira.weiny@intel.com> <20190606104203.GF7433@quack2.suse.cz> <20190606195114.GA30714@ziepe.ca> <20190606222228.GB11698@iweiny-DESK2.sc.intel.com> <20190607103636.GA12765@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190607103636.GA12765@quack2.suse.cz> User-Agent: Mutt/1.9.4 (2018-02-28) 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 Fri, Jun 07, 2019 at 12:36:36PM +0200, Jan Kara wrote: > Because the pins would be invisible to sysadmin from that point on. It is not invisible, it just shows up in a rdma specific kernel interface. You have to use rdma netlink to see the kernel object holding this pin. If this visibility is the main sticking point I suggest just enhancing the existing MR reporting to include the file info for current GUP pins and teaching lsof to collect information from there as well so it is easy to use. If the ownership of the lease transfers to the MR, and we report that ownership to userspace in a way lsof can find, then I think all the concerns that have been raised are met, right? > ugly to live so we have to come up with something better. The best I can > currently come up with is to have a method associated with the lease that > would invalidate the RDMA context that holds the pins in the same way that > a file close would do it. This is back to requiring all RDMA HW to have some new behavior they currently don't have.. The main objection to the current ODP & DAX solution is that very little HW can actually implement it, having the alternative still require HW support doesn't seem like progress. I think we will eventually start seein some HW be able to do this invalidation, but it won't be universal, and I'd rather leave it optional, for recovery from truely catastrophic errors (ie my DAX is on fire, I need to unplug it). Jason