From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 47A5CC43603 for ; Mon, 16 Dec 2019 04:18:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0FAFA2064B for ; Mon, 16 Dec 2019 04:18:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726638AbfLPERy (ORCPT ); Sun, 15 Dec 2019 23:17:54 -0500 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:48742 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726437AbfLPERx (ORCPT ); Sun, 15 Dec 2019 23:17:53 -0500 Received: from dread.disaster.area (pa49-195-139-249.pa.nsw.optusnet.com.au [49.195.139.249]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id D6D053A1320; Mon, 16 Dec 2019 15:17:49 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1ighpM-0007Vm-NT; Mon, 16 Dec 2019 15:17:48 +1100 Date: Mon, 16 Dec 2019 15:17:48 +1100 From: Dave Chinner To: Jens Axboe Cc: linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, willy@infradead.org, clm@fb.com, torvalds@linux-foundation.org Subject: Re: [PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes Message-ID: <20191216041748.GL19213@dread.disaster.area> References: <20191211152943.2933-1-axboe@kernel.dk> <20191211152943.2933-6-axboe@kernel.dk> <20191212223403.GH19213@dread.disaster.area> <39af5a4d-7539-5746-ac3e-e2d6bd2209e3@kernel.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <39af5a4d-7539-5746-ac3e-e2d6bd2209e3@kernel.dk> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=W5xGqiek c=1 sm=1 tr=0 a=KoypXv6BqLCQNZUs2nCMWg==:117 a=KoypXv6BqLCQNZUs2nCMWg==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=pxVhFHJ0LMsA:10 a=7-415B0cAAAA:8 a=ttecOIznnv4Bib-PtgkA:9 a=MxdZBAM7kpbZ0xAP:21 a=ww7lA5-8tPDbahhq:21 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Thu, Dec 12, 2019 at 05:57:57PM -0700, Jens Axboe wrote: > On 12/12/19 5:54 PM, Jens Axboe wrote: > > On 12/12/19 3:34 PM, Dave Chinner wrote: > >> On Wed, Dec 11, 2019 at 08:29:43AM -0700, Jens Axboe wrote: > >>> This adds support for RWF_UNCACHED for file systems using iomap to > >>> perform buffered writes. We use the generic infrastructure for this, > >>> by tracking pages we created and calling write_drop_cached_pages() > >>> to issue writeback and prune those pages. > >>> > >>> Signed-off-by: Jens Axboe > >>> --- > >>> fs/iomap/apply.c | 24 ++++++++++++++++++++++++ > >>> fs/iomap/buffered-io.c | 37 +++++++++++++++++++++++++++++-------- > >>> include/linux/iomap.h | 5 +++++ > >>> 3 files changed, 58 insertions(+), 8 deletions(-) > >>> > >>> diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c > >>> index 562536da8a13..966826ad4bb9 100644 > >>> --- a/fs/iomap/apply.c > >>> +++ b/fs/iomap/apply.c > >>> @@ -90,5 +90,29 @@ iomap_apply(struct inode *inode, loff_t pos, loff_t length, unsigned flags, > >>> flags, &iomap); > >>> } > >>> > >>> + if (written && (flags & IOMAP_UNCACHED)) { > >>> + struct address_space *mapping = inode->i_mapping; > >>> + > >>> + end = pos + written; > >>> + ret = filemap_write_and_wait_range(mapping, pos, end); > >>> + if (ret) > >>> + goto out; > >>> + > >>> + /* > >>> + * No pages were created for this range, we're done > >>> + */ > >>> + if (!(iomap.flags & IOMAP_F_PAGE_CREATE)) > >>> + goto out; > >>> + > >>> + /* > >>> + * Try to invalidate cache pages for the range we just wrote. > >>> + * We don't care if invalidation fails as the write has still > >>> + * worked and leaving clean uptodate pages in the page cache > >>> + * isn't a corruption vector for uncached IO. > >>> + */ > >>> + invalidate_inode_pages2_range(mapping, > >>> + pos >> PAGE_SHIFT, end >> PAGE_SHIFT); > >>> + } > >>> +out: > >>> return written ? written : ret; > >>> } > >> > >> Just a thought on further optimisation for this for XFS. > >> IOMAP_UNCACHED is being passed into the filesystem ->iomap_begin > >> methods by iomap_apply(). Hence the filesystems know that it is > >> an uncached IO that is being done, and we can tailor allocation > >> strategies to suit the fact that the data is going to be written > >> immediately. > >> > >> In this case, XFS needs to treat it the same way it treats direct > >> IO. That is, we do immediate unwritten extent allocation rather than > >> delayed allocation. This will reduce the allocation overhead and > >> will optimise for immediate IO locality rather than optimise for > >> delayed allocation. > >> > >> This should just be a relatively simple change to > >> xfs_file_iomap_begin() along the lines of: > >> > >> - if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && !(flags & IOMAP_DIRECT) && > >> - !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) { > >> + if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && > >> + !(flags & (IOMAP_DIRECT | IOMAP_UNCACHED)) && > >> + !IS_DAX(inode) && !xfs_get_extsz_hint(ip)) { > >> /* Reserve delalloc blocks for regular writeback. */ > >> return xfs_file_iomap_begin_delay(inode, offset, length, flags, > >> iomap); > >> } > >> > >> so that it avoids delayed allocation for uncached IO... > > > > That's very handy! Thanks, I'll add that to the next version. Just out > > of curiosity, would you prefer this as a separate patch, or just bundle > > it with the iomap buffered RWF_UNCACHED patch? I'm assuming the latter, > > and I'll just mention it in the changelog. > > OK, since it's in XFS, it'd be a separate patch. *nod* > The code you quote seems > to be something out-of-tree? Ah, I quoted the code in the 5.4 release branch, not the 5.5-rc1 tree. I'd forgotten that the xfs_file_iomap_begin() got massively refactored in the 5.5 merge and I hadn't updated my cscope trees. SO I'm guessing you want to go looking for the xfs_buffered_write_iomap_begin() and add another case to this initial branch: /* we can't use delayed allocations when using extent size hints */ if (xfs_get_extsz_hint(ip)) return xfs_direct_write_iomap_begin(inode, offset, count, flags, iomap, srcmap); To make the buffered write IO go down the direct IO allocation path... Cheers, Dave. -- Dave Chinner david@fromorbit.com