Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755881Ab3I3OvQ (ORCPT ); Mon, 30 Sep 2013 10:51:16 -0400 Received: from mail-qa0-f47.google.com ([209.85.216.47]:65228 "EHLO mail-qa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755431Ab3I3OvM (ORCPT ); Mon, 30 Sep 2013 10:51:12 -0400 MIME-Version: 1.0 X-Originating-IP: [86.59.245.170] In-Reply-To: <20130930143432.GG16579@fieldses.org> 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> Date: Mon, 30 Sep 2013 16:51:10 +0200 Message-ID: Subject: Re: [RFC] extending splice for copy offloading From: Miklos Szeredi To: "J. Bruce Fields" Cc: Ric Wheeler , "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 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1450 Lines: 32 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 -- 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/