From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Wed, 12 Jun 2019 15:13:36 -0700 From: Ira Weiny Subject: Re: [PATCH RFC 00/10] RDMA/FS DAX truncate proposal Message-ID: <20190612221336.GA27080@iweiny-DESK2.sc.intel.com> References: <20190606104203.GF7433@quack2.suse.cz> <20190606195114.GA30714@ziepe.ca> <20190606222228.GB11698@iweiny-DESK2.sc.intel.com> <20190607103636.GA12765@quack2.suse.cz> <20190607121729.GA14802@ziepe.ca> <20190607145213.GB14559@iweiny-DESK2.sc.intel.com> <20190612102917.GB14578@quack2.suse.cz> <20190612114721.GB3876@ziepe.ca> <20190612120907.GC14578@quack2.suse.cz> <20190612191421.GM3876@ziepe.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190612191421.GM3876@ziepe.ca> Sender: owner-linux-mm@kvack.org To: Jason Gunthorpe Cc: Jan Kara , Dan Williams , Theodore Ts'o , Jeff Layton , Dave Chinner , Matthew Wilcox , linux-xfs@vger.kernel.org, Andrew Morton , John Hubbard , =?iso-8859-1?B?Suly9G1l?= 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 List-ID: On Wed, Jun 12, 2019 at 04:14:21PM -0300, Jason Gunthorpe wrote: > On Wed, Jun 12, 2019 at 02:09:07PM +0200, Jan Kara wrote: > > On Wed 12-06-19 08:47:21, Jason Gunthorpe wrote: > > > On Wed, Jun 12, 2019 at 12:29:17PM +0200, Jan Kara wrote: > > > > > > > > > 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). > > > > > > > > > > Agreed. I think software wise there is not much some of the devices can do > > > > > with such an "invalidate". > > > > > > > > So out of curiosity: What does RDMA driver do when userspace just closes > > > > the file pointing to RDMA object? It has to handle that somehow by aborting > > > > everything that's going on... And I wanted similar behavior here. > > > > > > It aborts *everything* connected to that file descriptor. Destroying > > > everything avoids creating inconsistencies that destroying a subset > > > would create. > > > > > > What has been talked about for lease break is not destroying anything > > > but very selectively saying that one memory region linked to the GUP > > > is no longer functional. > > > > OK, so what I had in mind was that if RDMA app doesn't play by the rules > > and closes the file with existing pins (and thus layout lease) we would > > force it to abort everything. Yes, it is disruptive but then the app didn't > > obey the rule that it has to maintain file lease while holding pins. Thus > > such situation should never happen unless the app is malicious / buggy. > > We do have the infrastructure to completely revoke the entire > *content* of a FD (this is called device disassociate). It is > basically close without the app doing close. But again it only works > with some drivers. However, this is more likely something a driver > could support without a HW change though. > > It is quite destructive as it forcibly kills everything RDMA related > the process(es) are doing, but it is less violent than SIGKILL, and > there is perhaps a way for the app to recover from this, if it is > coded for it. I don't think many are... I think most would effectively be "killed" if this happened to them. > > My preference would be to avoid this scenario, but if it is really > necessary, we could probably build it with some work. > > The only case we use it today is forced HW hot unplug, so it is rarely > used and only for an 'emergency' like use case. I'd really like to avoid this as well. I think it will be very confusing for RDMA apps to have their context suddenly be invalid. I think if we have a way for admins to ID who is pinning a file the admin can take more appropriate action on those processes. Up to and including killing the process. Ira