Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755851AbbEZQFe (ORCPT ); Tue, 26 May 2015 12:05:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53588 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753193AbbEZQFa (ORCPT ); Tue, 26 May 2015 12:05:30 -0400 Date: Tue, 26 May 2015 12:04:01 -0400 From: Mike Snitzer To: Ming Lin Cc: 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 Subject: Re: [PATCH v4 01/11] block: make generic_make_request handle arbitrarily sized bios Message-ID: <20150526160400.GB4715@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> 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 Content-Length: 2831 Lines: 60 On Tue, May 26 2015 at 11:02am -0400, Ming Lin wrote: > 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. That'll result in quite large bios and always needing splitting. As Alasdair asked: please provide some performance data that justifies these changes. E.g use a setup like: XFS on a DM striped target. We can iterate on more complex setups once we have established some basic tests. If you're just punting to reviewers to do the testing for you that isn't going to instill _any_ confidence in me for this patchset as a suitabe replacement relative to performance. -- 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/