From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756650Ab2IUAe1 (ORCPT ); Thu, 20 Sep 2012 20:34:27 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:56734 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755075Ab2IUAeZ (ORCPT ); Thu, 20 Sep 2012 20:34:25 -0400 Date: Thu, 20 Sep 2012 17:34:22 -0700 From: Kent Overstreet To: Tejun Heo Cc: linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, axboe@kernel.dk, neilb@suse.de Subject: Re: [PATCH v2 19/26] bounce: Refactor __blk_queue_bounce to not use bi_io_vec Message-ID: <20120921003422.GN5519@google.com> References: <1347322957-25260-1-git-send-email-koverstreet@google.com> <1347322957-25260-20-git-send-email-koverstreet@google.com> <20120921002706.GW7264@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120921002706.GW7264@google.com> 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 Thu, Sep 20, 2012 at 05:27:06PM -0700, Tejun Heo wrote: > On Mon, Sep 10, 2012 at 05:22:30PM -0700, Kent Overstreet wrote: > > A bunch of what __blk_queue_bounce() was doing was problematic for the > > immutable bvec work; this cleans that up and the code is quite a bit > > smaller, too. > > > > The __bio_for_each_segment() in copy_to_high_bio_irq() was changed > > because that one's looping over the original bio, not the bounce bio - > > since the bounce code doesn't own that bio the __ version wasn't > > correct. > > Also, I can't understand the above at all. I can think why it > wouldn't be necessary but why is it wrong because bounce code doesn't > own it? Another prep work thing - in current code, it isn't really wrong (slightly inconsistent though). But the idea is that anything that doesn't own the bio shouldn't assume anything about bi_idx; the bounce code should loop over the bio starting from wherever it was when the bio got to the bounce code, not the start of the bio. A later patch makes this clearer - __bio_for_each_segment() gets removed in favor of bio_for_each_segment_all(), and it documents that bio_for_each_segment_all() is only for code that owns the bio.