Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754083AbbEZPCV (ORCPT ); Tue, 26 May 2015 11:02:21 -0400 Received: from mail.kernel.org ([198.145.29.136]:59188 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752669AbbEZPCT (ORCPT ); Tue, 26 May 2015 11:02:19 -0400 MIME-Version: 1.0 In-Reply-To: <20150526143626.GA4315@redhat.com> References: <1432318723-18829-1-git-send-email-mlin@kernel.org> <1432318723-18829-2-git-send-email-mlin@kernel.org> <20150526143626.GA4315@redhat.com> Date: Tue, 26 May 2015 08:02:08 -0700 Message-ID: Subject: Re: [PATCH v4 01/11] block: make generic_make_request handle arbitrarily sized bios From: Ming Lin To: Mike Snitzer Cc: Ming Lin , lkml , Christoph Hellwig , Kent Overstreet , Jens Axboe , Dongsu Park , Christoph Hellwig , Al Viro , Ming Lei , Neil Brown , Alasdair Kergon , dm-devel@redhat.com, Lars Ellenberg , drbd-user@lists.linbit.com, Jiri Kosina , Geoff Levand , Jim Paris , Joshua Morris , Philip Kelleher , Minchan Kim , Nitin Gupta , Oleg Drokin , Andreas Dilger 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: 2252 Lines: 52 On Tue, May 26, 2015 at 7:36 AM, Mike Snitzer wrote: > On Fri, May 22 2015 at 2:18pm -0400, > Ming Lin wrote: > >> From: Kent Overstreet >> >> The way the block layer is currently written, it goes to great lengths >> to avoid having to split bios; upper layer code (such as bio_add_page()) >> checks what the underlying device can handle and tries to always create >> bios that don't need to be split. >> >> But this approach becomes unwieldy and eventually breaks down with >> stacked devices and devices with dynamic limits, and it adds a lot of >> complexity. If the block layer could split bios as needed, we could >> eliminate a lot of complexity elsewhere - particularly in stacked >> drivers. Code that creates bios can then create whatever size bios are >> convenient, and more importantly stacked drivers don't have to deal with >> both their own bio size limitations and the limitations of the >> (potentially multiple) devices underneath them. In the future this will >> let us delete merge_bvec_fn and a bunch of other code. > > This series doesn't take any steps to train upper layers > (e.g. filesystems) to size their bios larger (which is defined as > "whatever size bios are convenient" above). > > bio_add_page(), and merge_bvec_fn, served as the means for upper layers > (and direct IO) to build up optimally sized bios. Without a replacement > (that I can see anyway) how is this patchset making forward progress > (getting Acks, etc)!? > > I like the idea of reduced complexity associated with these late bio > splitting changes I'm just not seeing how this is ready given there are > no upper layer changes that speak to building larger bios.. > > What am I missing? See: [PATCH v4 02/11] block: simplify bio_add_page() https://lkml.org/lkml/2015/5/22/754 Now bio_add_page() can build lager bios. And blk_queue_split() can split the bios in ->make_request() if needed. Thanks. > > Please advise, thanks! > Mike -- 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/