Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755096Ab3IYTG7 (ORCPT ); Wed, 25 Sep 2013 15:06:59 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46803 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751242Ab3IYTG6 (ORCPT ); Wed, 25 Sep 2013 15:06:58 -0400 Date: Wed, 25 Sep 2013 12:06:20 -0700 From: Zach Brown To: Anna Schumaker Cc: Szeredi Miklos , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, "linux-nfs@vger.kernel.org" , Trond Myklebust , Bryan Schumaker , "Martin K. Petersen" , Jens Axboe , Mark Fasheh , Joel Becker , Eric Wong Subject: Re: [RFC] extending splice for copy offloading Message-ID: <20130925190620.GB30372@lenny.home.zabbo.net> References: <1378919210-10372-1-git-send-email-zab@redhat.com> <20130925183828.GA30372@lenny.home.zabbo.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1941 Lines: 40 On Wed, Sep 25, 2013 at 03:02:29PM -0400, Anna Schumaker wrote: > On Wed, Sep 25, 2013 at 2:38 PM, Zach Brown wrote: > > > > Hrmph. I had composed a reply to you during Plumbers but.. something > > happened to it :). Here's another try now that I'm back. > > > >> > Some things to talk about: > >> > - I really don't care about the naming here. If you do, holler. > >> > - We might want different flags for file-to-file splicing and acceleration > >> > >> Yes, I think "copy" and "reflink" needs to be differentiated. > > > > I initially agreed but I'm not so sure now. The problem is that we > > can't know whether the acceleration is copying or not. XCOPY on some > > array may well do some shared referencing tricks. The nfs COPY op can > > have a server use btrfs reflink, or ext* and XCOPY, or .. who knows. At > > some point we have to admit that we have no way to determine the > > relative durability of writes. Storage can do a lot to make writes more > > or less fragile that we have no visibility of. SSD FTLs can log a bunch > > of unrelated sectors on to one flash failure domain. > > > > And if such a flag couldn't *actually* guarantee anything for a bunch of > > storage topologies, well, let's not bother with it. > > > > The only flag I'm in favour of now is one that has splice return rather > > than falling back to manual page cache reads and writes. It's more like > > O_NONBLOCK than any kind of data durability hint. > > For reference, I'm planning to have the NFS server do the fallback > when it copies since any local copy will be faster than a read and > write over the network. Agreed, this is definitely the reasonable thing to do. - z -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/