From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 In-Reply-To: References: <149766213493.22552.4057048843646200083.stgit@dwillia2-desk3.amr.corp.intel.com> <20170619132107.GG11993@dastard> <20170620004653.GI17542@dastard> <20170620084924.GA9752@lst.de> From: Andy Lutomirski Date: Tue, 20 Jun 2017 09:26:59 -0700 Message-ID: Subject: Re: [RFC PATCH 2/2] mm, fs: daxfile, an interface for byte-addressable updates to pmem To: Dan Williams Cc: Christoph Hellwig , Andy Lutomirski , Dave Chinner , Ross Zwisler , "Rudoff, Andy" , Andrew Morton , Jan Kara , linux-nvdimm , Linux API , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Jeff Moyer , Linux FS Devel Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: On Tue, Jun 20, 2017 at 9:17 AM, Dan Williams wrote: > On Tue, Jun 20, 2017 at 1:49 AM, Christoph Hellwig wrote: >> [stripped giant fullquotes] >> >> On Mon, Jun 19, 2017 at 10:53:12PM -0700, Andy Lutomirski wrote: >>> But that's my whole point. The kernel doesn't really need to prevent >>> all these background maintenance operations -- it just needs to block >>> .page_mkwrite until they are synced. I think that whatever new >>> mechanism we add for this should be sticky, but I see no reason why >>> the filesystem should have to block reflink on a DAX file entirely. >> >> Agreed - IFF we want to support write through semantics this is the >> only somewhat feasible way. It still has massive downsides of forcing >> the full sync machinery to run from the page fauly handler, which >> I'm rather scared off, but that's still better than creating a magic >> special case that isn't managable at all. > > An immutable-extent DAX-file and a reflink-capable DAX-file are not > mutually exclusive, and I have yet to hear a need for reflink support > without fsync/msync. Instead I have heard the need for an immutable > file for RDMA purposes, especially for hardware that can't trigger an > mmu fault. The special management of an immutable file is acceptable > to get these capabilities. I guess this applies to any user of get_user_pages() on a DAX-mapped file. Hmm. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org