Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 11 Feb 2002 07:41:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 11 Feb 2002 07:41:43 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.101]:18311 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id ; Mon, 11 Feb 2002 07:41:31 -0500 Date: Mon, 11 Feb 2002 23:41:27 +0530 From: Suparna Bhattacharya To: Benjamin LaHaise Cc: linux-aio@kvack.org, linux-kernel@vger.kernel.org Subject: Re: patch: aio + bio for raw io Message-ID: <20020211234127.B8661@in.ibm.com> Reply-To: suparna@in.ibm.com In-Reply-To: <20020208025313.A11893@redhat.com> <20020208151009.A1810@in.ibm.com> <20020208170257.A12788@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i In-Reply-To: <20020208170257.A12788@redhat.com>; from bcrl@redhat.com on Fri, Feb 08, 2002 at 05:02:57PM -0500 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 08, 2002 at 05:02:57PM -0500, Benjamin LaHaise wrote: > On Fri, Feb 08, 2002 at 03:10:09PM +0530, Suparna Bhattacharya wrote: > > You chose to add a kvec_cb field to the bio structure rather than use > > bi_private ? > > Yup. I'm lazy. Also, the cb struct actually needs 2 pointers, so just > bi_private isn't enough. > > > For the raw path, you are OK since you never have to copy data out of > > the kvecs after i/o completion, and unmap_kvec only looks at veclet pages. > > So the fact block can change the offset and len fields in the veclets > > doesn't affect you, but thought I'd mention it as a point of caution > > anyhow ... > > Ugh. That sounds like something bio should not be doing. If someone > wants to fix it, such a patch would be much appreciated, otherwise it'll > wait until I'm back in Canada. I had posted a suggestion on lkml earlier about this problem and one way to fix this - at that time I was thinking of bio->bi_voffset field (the thought was that it could even be useful for cloning/splitting), and was waiting for a decision from Jens about it. (Your kvec_dst is another way :)) However I'm now wondering if the rq->hard_cur_sectors can be used to achieve a similar effect (won't help with splitting, but might suffice for the request transfer, without requiring new bio fields). > > -ben ------------------------------------------ >From suparna@in.ibm.com Fri Dec 28 15:50:06 2001 Date: Fri, 28 Dec 2001 15:50:06 -0500 From: Suparna Bhattacharya To: linux-kernel@vger.kernel.org Cc: axboe@suse.de Subject: bio_io_vec and kvecs integration Message-ID: <20011228155006.A1519@in.ibm.com> Reply-To: suparna@in.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.2.5i Status: RO Content-Length: 1831 Lines: 36 Since bio, aio and zero-copy networking code all make use of a similar representation of a memory vector or i/o currency, I was looking at what it would take at bio level to make sure that these descriptors can be passed down as is to the block layer (without having to translate or copy descriptors). Ben has already posted some patches to change bio and skbuff fragments to his kveclet representation. Once all these subsystems share the same representation, the next step is to be able to pass the vectors around as is. Some of the changes towards this sort of a thing went in during one of the early updates to bio. The bio structure was modified to maintain a pointer to the vector list, so it can point to a vector list sent down to it by the calling subsystem. Well, this change was also needed for bio cloning (for lvm etc) and that's all its been used for so far since we don't have kvecs in the kernel yet. I think just a little more work is needed to get bio layer to take in a vector directly. This is because currently the block layer could modify the bv_offset and bv_len fields in the vector directly (as part of end_that_request_first processing) in case the whole segment/veclet/bvec doesn't get transfered/completed in one shot. This could result in unexpected effects for the higher layer if it tried to interpret the vector or say copy data from it after the i/o completes. So, should we add a bi_voffset field, which can be used in conjunction with bi_vidx to locate exactly where to start the next i/o transfer from/to, and try to leave bv_offset and bv_len fields untouched during request processing ? Or is there some other way to do this ? One of these days we're going to have to sort out the kiobuf/kvec decision for 2.5, but that's probably a discussion for a little later. Regards Suparna - 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/