Return-Path: linux-nfs-owner@vger.kernel.org Received: from mx1.redhat.com ([209.132.183.28]:25341 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754080Ab3I3Oxe (ORCPT ); Mon, 30 Sep 2013 10:53:34 -0400 Message-ID: <52499026.3090802@redhat.com> Date: Mon, 30 Sep 2013 10:52:22 -0400 From: Ric Wheeler MIME-Version: 1.0 To: Miklos Szeredi CC: "J. Bruce Fields" , "Myklebust, Trond" , Zach Brown , Anna Schumaker , Kernel Mailing List , Linux-Fsdevel , "linux-nfs@vger.kernel.org" , "Schumaker, Bryan" , "Martin K. Petersen" , Jens Axboe , Mark Fasheh , Joel Becker , Eric Wong Subject: Re: [RFC] extending splice for copy offloading References: <20130925210742.GG30372@lenny.home.zabbo.net> <20130926185508.GO30372@lenny.home.zabbo.net> <5244A68F.906@redhat.com> <20130927200550.GA22640@fieldses.org> <20130927205013.GZ30372@lenny.home.zabbo.net> <4FA345DA4F4AE44899BD2B03EEEC2FA9467EF2D7@SACEXCMBX04-PRD.hq.netapp.com> <52474839.2080201@redhat.com> <20130930143432.GG16579@fieldses.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Sender: linux-nfs-owner@vger.kernel.org List-ID: On 09/30/2013 10:51 AM, Miklos Szeredi wrote: > On Mon, Sep 30, 2013 at 4:34 PM, J. Bruce Fields wrote: >>> My other worry is about interruptibility/restartability. Ideas? >>> >>> What happens on splice(from, to, 4G) and it's a non-reflink copy? >>> Can the page cache copy be made restartable? Or should splice() be >>> allowed to return a short count? What happens on (non-reflink) remote >>> copies and huge request sizes? >> If I were writing an application that required copies to be restartable, >> I'd probably use the largest possible range in the reflink case but >> break the copy into smaller chunks in the splice case. >> > The app really doesn't want to care about that. And it doesn't want > to care about restartability, etc.. It's something the *kernel* has > to care about. You just can't have uninterruptible syscalls that > sleep for a "long" time, otherwise first you'll just have annoyed > users pressing ^C in vain; then, if the sleep is even longer, warnings > about task sleeping too long. > > One idea is letting splice() return a short count, and so the app can > safely issue SIZE_MAX requests and the kernel can decide if it can > copy the whole file in one go or if it wants to do it in smaller > chunks. > > Thanks, > Miklos You cannot rely on a short count. That implies that an offloaded copy starts at byte 0 and the short count first bytes are all valid. I don't believe that is in fact required by all (any?) versions of the spec :) Best just to fail and restart the whole operation. Ric