Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750999AbWCVNIb (ORCPT ); Wed, 22 Mar 2006 08:08:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751170AbWCVNIb (ORCPT ); Wed, 22 Mar 2006 08:08:31 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:7957 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S1750999AbWCVNIa (ORCPT ); Wed, 22 Mar 2006 08:08:30 -0500 Date: Wed, 22 Mar 2006 14:08:24 +0100 From: Jens Axboe To: Andrew Morton , linux-kernel@vger.kernel.org, dm-devel@redhat.com Subject: Re: [dm-devel] Re: dm: bio split bvec fix Message-ID: <20060322130823.GH4285@suse.de> References: <20060320192155.GU4724@agk.surrey.redhat.com> <20060322113235.GC4285@suse.de> <20060322121941.GS26428@agk.surrey.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20060322121941.GS26428@agk.surrey.redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1558 Lines: 38 On Wed, Mar 22 2006, Alasdair G Kergon wrote: > On Wed, Mar 22, 2006 at 12:32:35PM +0100, Jens Axboe wrote: > > Why isn't this just handled in the merge callback? Can a single page bio > > span > 2 targets? > > Yes. (Unit of size if the sector - and things don't have to > be aligned nicely, just aligned to sector.) > > IIRC the merge function assumes the number of bytes that can > be added is only a function of the offset: but in our case > it's also a function of time. To make this work it should > reserve those bytes with device-mapper, and guarantee either to > supply them to us subsequently (and preferably quickly) or to > cancel that reservation. Device-mapper for its part would > guarantee to accept the bio without needing to split it. > Or dm could have a rejection mechanism that refuses bios > that are too big (because the max number of bytes we accept > got reduced between the initial call and the bio actually being > presented) and they go back and get processed again. > > Alasdair > -- > agk@redhat.com > - > 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/ > -- Jens Axboe - 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/