From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com ([209.132.183.28]:59030 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726108AbfC1OJK (ORCPT ); Thu, 28 Mar 2019 10:09:10 -0400 Date: Thu, 28 Mar 2019 10:08:59 -0400 From: Brian Foster Subject: Re: [RFC PATCH] xfs: implement per-inode writeback completion Message-ID: <20190328140859.GA17056@bfoster> References: <20190327030550.GZ1183@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327030550.GZ1183@magnolia> Sender: linux-xfs-owner@vger.kernel.org List-ID: List-Id: xfs To: "Darrick J. Wong" Cc: xfs On Tue, Mar 26, 2019 at 08:05:50PM -0700, Darrick J. Wong wrote: > Hi folks, > > Here's a quick patchset reworking writeback ioend completion processing > into per-inode completion queues so that we don't have a thundering herd > of unwritten/cow completion kworkers contending for the ILOCK. The > second patch will also combine adjacent ioends when possible to reduce > the overhead further. Let me know what you think. :) > I assume the issue is that you get a bunch of ioends associated with COW remaps or whatever and workqueue parallelism leads to a bunch contending on inode locks because they happen to be associated with the same inode. Hence, it's more efficient to have a single work item per inode, let that task complete as many ioends as available for the inode and let the workqueue spread around workers for different inodes. Sounds like a nice idea to me. Is there a workload that measurably benefits from this or is this just based on observation? A couple small nits.. > --D > --- > From: Darrick J. Wong > > Restructure the buffered writeback completion code to use a single work > item per inode, since it's pointless to awaken a thundering herd of > threads to contend on a single inode's ILOCK. > > Signed-off-by: Darrick J. Wong > --- > fs/xfs/xfs_aops.c | 48 +++++++++++++++++++++++++++++++++++++----------- > fs/xfs/xfs_aops.h | 1 - > fs/xfs/xfs_icache.c | 3 +++ > fs/xfs/xfs_inode.h | 7 +++++++ > 4 files changed, 47 insertions(+), 12 deletions(-) > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > index 3619e9e8d359..f7a9bb661826 100644 > --- a/fs/xfs/xfs_aops.c > +++ b/fs/xfs/xfs_aops.c > @@ -234,11 +234,9 @@ xfs_setfilesize_ioend( > * IO write completion. > */ > STATIC void > -xfs_end_io( > - struct work_struct *work) > +xfs_end_ioend( > + struct xfs_ioend *ioend) > { > - struct xfs_ioend *ioend = > - container_of(work, struct xfs_ioend, io_work); > struct xfs_inode *ip = XFS_I(ioend->io_inode); > xfs_off_t offset = ioend->io_offset; > size_t size = ioend->io_size; > @@ -278,19 +276,48 @@ xfs_end_io( > xfs_destroy_ioend(ioend, error); > } > > +/* Finish all pending io completions. */ > +void > +xfs_end_io( > + struct work_struct *work) > +{ > + struct xfs_inode *ip; > + struct xfs_ioend *ioend; > + struct list_head completion_list; > + unsigned long flags; > + > + ip = container_of(work, struct xfs_inode, i_iodone_work); > + > + spin_lock_irqsave(&ip->i_iodone_lock, flags); > + list_replace_init(&ip->i_iodone_list, &completion_list); > + spin_unlock_irqrestore(&ip->i_iodone_lock, flags); > + > + while (!list_empty(&completion_list)) { > + ioend = list_first_entry(&completion_list, struct xfs_ioend, > + io_list); > + list_del_init(&ioend->io_list); > + xfs_end_ioend(ioend); > + } > +} > + > STATIC void > xfs_end_bio( > struct bio *bio) > { > struct xfs_ioend *ioend = bio->bi_private; > - struct xfs_mount *mp = XFS_I(ioend->io_inode)->i_mount; > + struct xfs_inode *ip = XFS_I(ioend->io_inode); > + struct xfs_mount *mp = ip->i_mount; > + unsigned long flags; > > if (ioend->io_fork == XFS_COW_FORK || > - ioend->io_state == XFS_EXT_UNWRITTEN) > - queue_work(mp->m_unwritten_workqueue, &ioend->io_work); > - else if (ioend->io_append_trans) > - queue_work(mp->m_data_workqueue, &ioend->io_work); > - else > + ioend->io_state == XFS_EXT_UNWRITTEN || > + ioend->io_append_trans != NULL) { > + spin_lock_irqsave(&ip->i_iodone_lock, flags); > + if (list_empty(&ip->i_iodone_list)) > + queue_work(mp->m_unwritten_workqueue, &ip->i_iodone_work); > + list_add_tail(&ioend->io_list, &ip->i_iodone_list); > + spin_unlock_irqrestore(&ip->i_iodone_lock, flags); > + } else Ok, so there's no longer a need for multiple ioend workqueues because all such operations are going to be processed by the single work execution. Perhaps we should rename m_unwritten_workqueue or just use m_data_workqueue since it happens to have a more generic name. We can also kill off the other wq either way since it appears to be unused. > xfs_destroy_ioend(ioend, blk_status_to_errno(bio->bi_status)); > } > > @@ -594,7 +621,6 @@ xfs_alloc_ioend( > ioend->io_inode = inode; > ioend->io_size = 0; > ioend->io_offset = offset; > - INIT_WORK(&ioend->io_work, xfs_end_io); > ioend->io_append_trans = NULL; > ioend->io_bio = bio; > return ioend; > diff --git a/fs/xfs/xfs_aops.h b/fs/xfs/xfs_aops.h > index 6c2615b83c5d..f62b03186c62 100644 > --- a/fs/xfs/xfs_aops.h > +++ b/fs/xfs/xfs_aops.h > @@ -18,7 +18,6 @@ struct xfs_ioend { > struct inode *io_inode; /* file being written to */ > size_t io_size; /* size of the extent */ > xfs_off_t io_offset; /* offset in the file */ > - struct work_struct io_work; /* xfsdatad work queue */ > struct xfs_trans *io_append_trans;/* xact. for size update */ > struct bio *io_bio; /* bio being built */ > struct bio io_inline_bio; /* MUST BE LAST! */ > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index 245483cc282b..e70e7db29026 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -70,6 +70,9 @@ xfs_inode_alloc( > ip->i_flags = 0; > ip->i_delayed_blks = 0; > memset(&ip->i_d, 0, sizeof(ip->i_d)); > + INIT_WORK(&ip->i_iodone_work, xfs_end_io); > + INIT_LIST_HEAD(&ip->i_iodone_list); > + spin_lock_init(&ip->i_iodone_lock); > > return ip; > } > diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h > index e62074a5257c..88239c2dd824 100644 > --- a/fs/xfs/xfs_inode.h > +++ b/fs/xfs/xfs_inode.h > @@ -57,6 +57,11 @@ typedef struct xfs_inode { > > /* VFS inode */ > struct inode i_vnode; /* embedded VFS inode */ > + > + /* pending io completions */ > + spinlock_t i_iodone_lock; > + struct work_struct i_iodone_work; > + struct list_head i_iodone_list; A nit but I guess I'd name these with ioend instead of iodone. The latter kind of confuses with buffer iodone callbacks (to me). Brian > } xfs_inode_t; > > /* Convert from vfs inode to xfs inode */ > @@ -503,4 +508,6 @@ bool xfs_inode_verify_forks(struct xfs_inode *ip); > int xfs_iunlink_init(struct xfs_perag *pag); > void xfs_iunlink_destroy(struct xfs_perag *pag); > > +void xfs_end_io(struct work_struct *work); > + > #endif /* __XFS_INODE_H__ */