Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752606AbaANEss (ORCPT ); Mon, 13 Jan 2014 23:48:48 -0500 Received: from mail-pd0-f173.google.com ([209.85.192.173]:64114 "EHLO mail-pd0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751678AbaANEsp (ORCPT ); Mon, 13 Jan 2014 23:48:45 -0500 Date: Mon, 13 Jan 2014 20:48:41 -0800 From: Kent Overstreet To: "Martin K. Petersen" Cc: Hugh Dickins , Jens Axboe , Shaohua Li , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: next bio iters break discard? Message-ID: <20140114044841.GO9037@kmo> References: <20140114023346.GN9037@kmo> 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 On Mon, Jan 13, 2014 at 11:06:33PM -0500, Martin K. Petersen wrote: > >>>>> "Kent" == Kent Overstreet writes: > > Kent, > > Kent> I think for discards we can deal with this easily enough - > Kent> __blk_recalc_rq_segments() will have to special case them - but > Kent> there's a similar (but worse) issue with WRITE_SAME, and looking > Kent> at the code it does attempt to merge WRITE_SAME requests too. > > DISCARD bios have no payload going down the stack. They get a payload > attached in the sd driver and will therefore have a single bvec at > completion time. > > WRITE_SAME bios have a single bvec payload throughout their lifetime. > > For both these types of requests we never attempt to merge the actual > payloads. But the block range worked on may shrink or grow as the bio is > split or merged going down the stack. > > IOW, DISCARD, WRITE SAME and the impending COPY requests do not have a > 1:1 mapping between the block range worked on and the size of any bvecs > attached. Your recent changes must have changed the way we handled that > in the past. Yeah - but with WRITE_SAME bios, wouldn't we at least have to check that they're writing the same data to merge them? -- 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/