From: Jan Kara Subject: Re: [PATCH] fs, dax: unify IOMAP_F_DIRTY read vs write handling policy in the dax core Date: Tue, 14 Nov 2017 10:31:50 +0100 Message-ID: <20171114093150.GC7053@quack2.suse.cz> References: <151062258598.8554.8157038002895095232.stgit@dwillia2-desk3.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linux-nvdimm@lists.01.org, Jan Kara , "Darrick J. Wong" , Dave Chinner , linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, Ross Zwisler , linux-ext4@vger.kernel.org, Christoph Hellwig To: Dan Williams Return-path: Received: from mx2.suse.de ([195.135.220.15]:44395 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754097AbdKNJbx (ORCPT ); Tue, 14 Nov 2017 04:31:53 -0500 Content-Disposition: inline In-Reply-To: <151062258598.8554.8157038002895095232.stgit@dwillia2-desk3.amr.corp.intel.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon 13-11-17 17:27:54, Dan Williams wrote: > While reviewing whether MAP_SYNC should strengthen its current guarantee > of syncing writes from the initiating process to also include > third-party readers observing dirty metadata, Dave pointed out that the > check of IOMAP_WRITE is misplaced. > > The policy of what to with IOMAP_F_DIRTY should be separated from the > generic filesystem mechanism of reporting dirty metadata. Move this > policy to the fs-dax core to simplify the per-filesystem iomap handlers, > and further centralize code that implements the MAP_SYNC policy. This > otherwise should not change behavior, it just makes it easier to change > behavior in the future. > > Cc: Jan Kara > Cc: Christoph Hellwig > Cc: Darrick J. Wong > Cc: Ross Zwisler > Reported-by: Dave Chinner > Signed-off-by: Dan Williams > --- > This is an additional cleanup I want to include in the 4.15 merge > request for the MAP_SYNC feature. Please review, I'm looking to send the > pull request towards the end of the week. The patch looks fine to me. You can add: Reviewed-by: Jan Kara Honza > > > fs/dax.c | 15 +++++++++++++-- > fs/ext4/inode.c | 2 +- > fs/xfs/xfs_iomap.c | 6 +++--- > 3 files changed, 17 insertions(+), 6 deletions(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 78233c716757..27ba300660ff 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -1079,6 +1079,17 @@ static int dax_fault_return(int error) > return VM_FAULT_SIGBUS; > } > > +/* > + * MAP_SYNC on a dax mapping guarantees dirty metadata is > + * flushed on write-faults (non-cow), but not read-faults. > + */ > +static bool dax_fault_is_synchronous(unsigned long flags, > + struct vm_area_struct *vma, struct iomap *iomap) > +{ > + return (flags & IOMAP_WRITE) && (vma->vm_flags & VM_SYNC) > + && (iomap->flags & IOMAP_F_DIRTY); > +} > + > static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp, > const struct iomap_ops *ops) > { > @@ -1170,7 +1181,7 @@ static int dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp, > goto finish_iomap; > } > > - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY); > + sync = dax_fault_is_synchronous(flags, vma, &iomap); > > switch (iomap.type) { > case IOMAP_MAPPED: > @@ -1390,7 +1401,7 @@ static int dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp, > if (iomap.offset + iomap.length < pos + PMD_SIZE) > goto finish_iomap; > > - sync = (vma->vm_flags & VM_SYNC) && (iomap.flags & IOMAP_F_DIRTY); > + sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap); > > switch (iomap.type) { > case IOMAP_MAPPED: > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 13a198924a0f..ee4d907a4251 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -3479,7 +3479,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length, > } > > iomap->flags = 0; > - if ((flags & IOMAP_WRITE) && ext4_inode_datasync_dirty(inode)) > + if (ext4_inode_datasync_dirty(inode)) > iomap->flags |= IOMAP_F_DIRTY; > iomap->bdev = inode->i_sb->s_bdev; > iomap->dax_dev = sbi->s_daxdev; > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > index b43be199fbdf..888b60189983 100644 > --- a/fs/xfs/xfs_iomap.c > +++ b/fs/xfs/xfs_iomap.c > @@ -1087,9 +1087,9 @@ xfs_file_iomap_begin( > trace_xfs_iomap_found(ip, offset, length, 0, &imap); > } > > - if ((flags & IOMAP_WRITE) && xfs_ipincount(ip) && > - (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP)) > - iomap->flags |= IOMAP_F_DIRTY; > + if (xfs_ipincount(ip)) > + if (ip->i_itemp->ili_fsync_fields & ~XFS_ILOG_TIMESTAMP) > + iomap->flags |= IOMAP_F_DIRTY; > > xfs_bmbt_to_iomap(ip, iomap, &imap); > > -- Jan Kara SUSE Labs, CR