From patchwork Wed May 2 05:38:07 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Dave Chinner X-Patchwork-Id: 10374961 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A4C7960384 for ; Wed, 2 May 2018 06:02:16 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 954B928D62 for ; Wed, 2 May 2018 06:02:16 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 855EB28D63; Wed, 2 May 2018 06:02:16 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 1954528D6A for ; Wed, 2 May 2018 06:02:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750999AbeEBGCN (ORCPT ); Wed, 2 May 2018 02:02:13 -0400 Received: from ipmail03.adl2.internode.on.net ([150.101.137.141]:28044 "EHLO ipmail03.adl2.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751045AbeEBGCJ (ORCPT ); Wed, 2 May 2018 02:02:09 -0400 Received: from ppp59-167-129-252.static.internode.on.net (HELO dastard) ([59.167.129.252]) by ipmail03.adl2.internode.on.net with ESMTP; 02 May 2018 15:08:13 +0930 Received: from discord.disaster.area ([192.168.1.111]) by dastard with esmtp (Exim 4.80) (envelope-from ) id 1fDkSx-0002NE-Vq; Wed, 02 May 2018 15:38:12 +1000 Received: from dave by discord.disaster.area with local (Exim 4.91) (envelope-from ) id 1fDkSx-0003dp-UA; Wed, 02 May 2018 15:38:11 +1000 From: Dave Chinner To: linux-xfs@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, hch@lst.de, rdorr@microsoft.com Subject: [PATCH 3/3] iomap: Use FUA for pure data O_DSYNC DIO writes Date: Wed, 2 May 2018 15:38:07 +1000 Message-Id: <20180502053807.13846-4-david@fromorbit.com> X-Mailer: git-send-email 2.17.0 In-Reply-To: <20180502053807.13846-1-david@fromorbit.com> References: <20180502053807.13846-1-david@fromorbit.com> Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Dave Chinner If we are doing direct IO writes with datasync semantics, we often have to flush metadata changes along with the data write. However, if we are overwriting existing data, there are no metadata changes that we need to flush. In this case, optimising the IO by using FUA write makes sense. We know from the IOMAP_F_DIRTY flag as to whether a specific inode requires a metadata flush - this is currently used by DAX to ensure extent modification as stable in page fault operations. For direct IO writes, we can use it to determine if we need to flush metadata or not once the data is on disk. Hence if we have been returned a mapped extent that is not new and the IO mapping is not dirty, then we can use a FUA write to provide datasync semantics. This allows us to short-cut the generic_write_sync() call in IO completion and hence avoid unnecessary operations. This makes pure direct IO data write behaviour identical to the way block devices use REQ_FUA to provide datasync semantics. On a FUA enabled device, a synchronous direct IO write workload (sequential 4k overwrites in 32MB file) had the following results: # xfs_io -fd -c "pwrite -V 1 -D 0 32m" /mnt/scratch/boo kernel time write()s write iops Write b/w ------ ---- -------- ---------- --------- (no dsync) 4s 2173/s 2173 8.5MB/s vanilla 22s 370/s 750 1.4MB/s patched 19s 420/s 420 1.6MB/s The patched code clearly doesn't send cache flushes anymore, but instead uses FUA (confirmed via blktrace), and performance improves a bit as a result. However, the benefits will be higher on workloads that mix O_DSYNC overwrites with other write IO as we won't be flushing the entire device cache on every DSYNC overwrite IO anymore. Signed-Off-By: Dave Chinner Reviewed-by: Christoph Hellwig --- fs/iomap.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 46 insertions(+), 5 deletions(-) diff --git a/fs/iomap.c b/fs/iomap.c index b044d8ee2efd..bcfd7f3654d4 100644 --- a/fs/iomap.c +++ b/fs/iomap.c @@ -685,6 +685,7 @@ EXPORT_SYMBOL_GPL(iomap_seek_data); * Private flags for iomap_dio, must not overlap with the public ones in * iomap.h: */ +#define IOMAP_DIO_WRITE_FUA (1 << 28) #define IOMAP_DIO_NEED_SYNC (1 << 29) #define IOMAP_DIO_WRITE (1 << 30) #define IOMAP_DIO_DIRTY (1 << 31) @@ -861,6 +862,7 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, struct iov_iter iter; struct bio *bio; bool need_zeroout = false; + bool use_fua = false; int nr_pages, ret; size_t copied = 0; @@ -884,8 +886,20 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, case IOMAP_MAPPED: if (iomap->flags & IOMAP_F_SHARED) dio->flags |= IOMAP_DIO_COW; - if (iomap->flags & IOMAP_F_NEW) + if (iomap->flags & IOMAP_F_NEW) { need_zeroout = true; + } else { + /* + * Use a FUA write if we need datasync semantics, this + * is a pure data IO that doesn't require any metadata + * updates and the underlying device supports FUA. This + * allows us to avoid cache flushes on IO completion. + */ + if (!(iomap->flags & (IOMAP_F_SHARED|IOMAP_F_DIRTY)) && + (dio->flags & IOMAP_DIO_WRITE_FUA) && + blk_queue_fua(bdev_get_queue(iomap->bdev))) + use_fua = true; + } break; default: WARN_ON_ONCE(1); @@ -933,10 +947,14 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, n = bio->bi_iter.bi_size; if (dio->flags & IOMAP_DIO_WRITE) { - bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC | REQ_IDLE); + bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE; + if (use_fua) + bio->bi_opf |= REQ_FUA; + else + dio->flags &= ~IOMAP_DIO_WRITE_FUA; task_io_account_write(n); } else { - bio_set_op_attrs(bio, REQ_OP_READ, 0); + bio->bi_opf = REQ_OP_READ; if (dio->flags & IOMAP_DIO_DIRTY) bio_set_pages_dirty(bio); } @@ -966,7 +984,12 @@ iomap_dio_actor(struct inode *inode, loff_t pos, loff_t length, /* * iomap_dio_rw() always completes O_[D]SYNC writes regardless of whether the IO - * is being issued as AIO or not. + * is being issued as AIO or not. This allows us to optimise pure data writes + * to use REQ_FUA rather than requiring generic_write_sync() to issue a + * REQ_FLUSH post write. This is slightly tricky because a single request here + * can be mapped into multiple disjoint IOs and only a subset of the IOs issued + * may be pure data writes. In that case, we still need to do a full data sync + * completion. */ ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, @@ -1012,10 +1035,21 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, if (iter->type == ITER_IOVEC) dio->flags |= IOMAP_DIO_DIRTY; } else { + flags |= IOMAP_WRITE; dio->flags |= IOMAP_DIO_WRITE; + + /* for data sync or sync, we need sync completion processing */ if (iocb->ki_flags & IOCB_DSYNC) dio->flags |= IOMAP_DIO_NEED_SYNC; - flags |= IOMAP_WRITE; + + /* + * For datasync only writes, we optimistically try using FUA for + * this IO. Any non-FUA write that occurs will clear this flag, + * hence we know before completion whether a cache flush is + * necessary. + */ + if ((iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC)) == IOCB_DSYNC) + dio->flags |= IOMAP_DIO_WRITE_FUA; } if (iocb->ki_flags & IOCB_NOWAIT) { @@ -1071,6 +1105,13 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter, if (ret < 0) iomap_dio_set_error(dio, ret); + /* + * If all the writes we issued were FUA, we don't need to flush the + * cache on IO completion. Clear the sync flag for this case. + */ + if (dio->flags & IOMAP_DIO_WRITE_FUA) + dio->flags &= ~IOMAP_DIO_NEED_SYNC; + if (!atomic_dec_and_test(&dio->ref)) { if (!is_sync_kiocb(iocb)) return -EIOCBQUEUED;